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pth(3)			     GNU Portable Threads			pth(3)

NAME
       pth - GNU Portable Threads

VERSION
       GNU Pth 2.0.7 (08-Jun-2006)

SYNOPSIS
       Global Library Management
	   pth_init, pth_kill, pth_ctrl, pth_version.

       Thread Attribute Handling
	   pth_attr_of, pth_attr_new, pth_attr_init, pth_attr_set,
	   pth_attr_get, pth_attr_destroy.

       Thread Control
	   pth_spawn, pth_once, pth_self, pth_suspend, pth_resume, pth_yield,
	   pth_nap, pth_wait, pth_cancel, pth_abort, pth_raise, pth_join,
	   pth_exit.

       Utilities
	   pth_fdmode, pth_time, pth_timeout, pth_sfiodisc.

       Cancellation Management
	   pth_cancel_point, pth_cancel_state.

       Event Handling
	   pth_event, pth_event_typeof, pth_event_extract, pth_event_concat,
	   pth_event_isolate, pth_event_walk, pth_event_status,
	   pth_event_free.

       Key-Based Storage
	   pth_key_create, pth_key_delete, pth_key_setdata, pth_key_getdata.

       Message Port Communication
	   pth_msgport_create, pth_msgport_destroy, pth_msgport_find, pth_msg‐
	   port_pending, pth_msgport_put, pth_msgport_get, pth_msgport_reply.

       Thread Cleanups
	   pth_cleanup_push, pth_cleanup_pop.

       Process Forking
	   pth_atfork_push, pth_atfork_pop, pth_fork.

       Synchronization
	   pth_mutex_init, pth_mutex_acquire, pth_mutex_release,
	   pth_rwlock_init, pth_rwlock_acquire, pth_rwlock_release,
	   pth_cond_init, pth_cond_await, pth_cond_notify, pth_barrier_init,
	   pth_barrier_reach.

       User-Space Context
	   pth_uctx_create, pth_uctx_make, pth_uctx_switch, pth_uctx_destroy.

       Generalized POSIX Replacement API
	   pth_sigwait_ev, pth_accept_ev, pth_connect_ev, pth_select_ev,
	   pth_poll_ev, pth_read_ev, pth_readv_ev, pth_write_ev,
	   pth_writev_ev, pth_recv_ev, pth_recvfrom_ev, pth_send_ev,
	   pth_sendto_ev.

       Standard POSIX Replacement API
	   pth_nanosleep, pth_usleep, pth_sleep, pth_waitpid, pth_system,
	   pth_sigmask, pth_sigwait, pth_accept, pth_connect, pth_select,
	   pth_pselect, pth_poll, pth_read, pth_readv, pth_write, pth_writev,
	   pth_pread, pth_pwrite, pth_recv, pth_recvfrom, pth_send,
	   pth_sendto.

DESCRIPTION
	 ____  _   _
	⎪  _ \⎪ ⎪_⎪ ⎪__
	⎪ ⎪_) ⎪ __⎪ '_ \	 ``Only those who attempt
	⎪  __/⎪ ⎪_⎪ ⎪ ⎪ ⎪	   the absurd can achieve
	⎪_⎪    \__⎪_⎪ ⎪_⎪	   the impossible.''

       Pth is a very portable POSIX/ANSI-C based library for Unix platforms
       which provides non-preemptive priority-based scheduling for multiple
       threads of execution (aka `multithreading') inside event-driven appli‐
       cations. All threads run in the same address space of the application
       process, but each thread has its own individual program counter, run-
       time stack, signal mask and "errno" variable.

       The thread scheduling itself is done in a cooperative way, i.e., the
       threads are managed and dispatched by a priority- and event-driven non-
       preemptive scheduler. The intention is that this way both better porta‐
       bility and run-time performance is achieved than with preemptive sched‐
       uling. The event facility allows threads to wait until various types of
       internal and external events occur, including pending I/O on file
       descriptors, asynchronous signals, elapsed timers, pending I/O on mes‐
       sage ports, thread and process termination, and even results of custom‐
       ized callback functions.

       Pth also provides an optional emulation API for POSIX.1c threads
       (`Pthreads') which can be used for backward compatibility to existing
       multithreaded applications. See Pth's pthread(3) manual page for
       details.

       Threading Background

       When programming event-driven applications, usually servers, lots of
       regular jobs and one-shot requests have to be processed in parallel.
       To efficiently simulate this parallel processing on uniprocessor
       machines, we use `multitasking' -- that is, we have the application ask
       the operating system to spawn multiple instances of itself. On Unix,
       typically the kernel implements multitasking in a preemptive and prior‐
       ity-based way through heavy-weight processes spawned with fork(2).
       These processes usually do not share a common address space. Instead
       they are clearly separated from each other, and are created by direct
       cloning a process address space (although modern kernels use memory
       segment mapping and copy-on-write semantics to avoid unnecessary copy‐
       ing of physical memory).

       The drawbacks are obvious: Sharing data between the processes is com‐
       plicated, and can usually only be done efficiently through shared mem‐
       ory (but which itself is not very portable). Synchronization is compli‐
       cated because of the preemptive nature of the Unix scheduler (one has
       to use atomic locks, etc). The machine's resources can be exhausted
       very quickly when the server application has to serve too many long-
       running requests (heavy-weight processes cost memory). And when each
       request spawns a sub-process to handle it, the server performance and
       responsiveness is horrible (heavy-weight processes cost time to spawn).
       Finally, the server application doesn't scale very well with the load
       because of these resource problems. In practice, lots of tricks are
       usually used to overcome these problems - ranging from pre-forked sub-
       process pools to semi-serialized processing, etc.

       One of the most elegant ways to solve these resource- and data-sharing
       problems is to have multiple light-weight threads of execution inside a
       single (heavy-weight) process, i.e., to use multithreading.  Those
       threads usually improve responsiveness and performance of the applica‐
       tion, often improve and simplify the internal program structure, and
       most important, require less system resources than heavy-weight pro‐
       cesses. Threads are neither the optimal run-time facility for all types
       of applications, nor can all applications benefit from them. But at
       least event-driven server applications usually benefit greatly from
       using threads.

       The World of Threading

       Even though lots of documents exists which describe and define the
       world of threading, to understand Pth, you need only basic knowledge
       about threading. The following definitions of thread-related terms
       should at least help you understand thread programming enough to allow
       you to use Pth.

       o process vs. thread
	 A process on Unix systems consists of at least the following funda‐
	 mental ingredients: virtual memory table, program code, program
	 counter, heap memory, stack memory, stack pointer, file descriptor
	 set, signal table. On every process switch, the kernel saves and
	 restores these ingredients for the individual processes. On the other
	 hand, a thread consists of only a private program counter, stack mem‐
	 ory, stack pointer and signal table. All other ingredients, in par‐
	 ticular the virtual memory, it shares with the other threads of the
	 same process.

       o kernel-space vs. user-space threading
	 Threads on a Unix platform traditionally can be implemented either
	 inside kernel-space or user-space. When threads are implemented by
	 the kernel, the thread context switches are performed by the kernel
	 without the application's knowledge. Similarly, when threads are
	 implemented in user-space, the thread context switches are performed
	 by an application library, without the kernel's knowledge. There also
	 are hybrid threading approaches where, typically, a user-space
	 library binds one or more user-space threads to one or more kernel-
	 space threads (there usually called light-weight processes - or in
	 short LWPs).

	 User-space threads are usually more portable and can perform faster
	 and cheaper context switches (for instance via swapcontext(2) or
	 setjmp(3)/longjmp(3)) than kernel based threads. On the other hand,
	 kernel-space threads can take advantage of multiprocessor machines
	 and don't have any inherent I/O blocking problems. Kernel-space
	 threads are usually scheduled in preemptive way side-by-side with the
	 underlying processes. User-space threads on the other hand use either
	 preemptive or non-preemptive scheduling.

       o preemptive vs. non-preemptive thread scheduling
	 In preemptive scheduling, the scheduler lets a thread execute until a
	 blocking situation occurs (usually a function call which would block)
	 or the assigned timeslice elapses. Then it detracts control from the
	 thread without a chance for the thread to object. This is usually
	 realized by interrupting the thread through a hardware interrupt sig‐
	 nal (for kernel-space threads) or a software interrupt signal (for
	 user-space threads), like "SIGALRM" or "SIGVTALRM". In non-preemptive
	 scheduling, once a thread received control from the scheduler it
	 keeps it until either a blocking situation occurs (again a function
	 call which would block and instead switches back to the scheduler) or
	 the thread explicitly yields control back to the scheduler in a coop‐
	 erative way.

       o concurrency vs. parallelism
	 Concurrency exists when at least two threads are in progress at the
	 same time. Parallelism arises when at least two threads are executing
	 simultaneously. Real parallelism can be only achieved on multiproces‐
	 sor machines, of course. But one also usually speaks of parallelism
	 or high concurrency in the context of preemptive thread scheduling
	 and of low concurrency in the context of non-preemptive thread sched‐
	 uling.

       o responsiveness
	 The responsiveness of a system can be described by the user visible
	 delay until the system responses to an external request. When this
	 delay is small enough and the user doesn't recognize a noticeable
	 delay, the responsiveness of the system is considered good. When the
	 user recognizes or is even annoyed by the delay, the responsiveness
	 of the system is considered bad.

       o reentrant, thread-safe and asynchronous-safe functions
	 A reentrant function is one that behaves correctly if it is called
	 simultaneously by several threads and then also executes simultane‐
	 ously.	 Functions that access global state, such as memory or files,
	 of course, need to be carefully designed in order to be reentrant.
	 Two traditional approaches to solve these problems are caller-sup‐
	 plied states and thread-specific data.

	 Thread-safety is the avoidance of data races, i.e., situations in
	 which data is set to either correct or incorrect value depending upon
	 the (unpredictable) order in which multiple threads access and modify
	 the data. So a function is thread-safe when it still behaves semanti‐
	 cally correct when called simultaneously by several threads (it is
	 not required that the functions also execute simultaneously). The
	 traditional approach to achieve thread-safety is to wrap a function
	 body with an internal mutual exclusion lock (aka `mutex'). As you
	 should recognize, reentrant is a stronger attribute than thread-safe,
	 because it is harder to achieve and results especially in no run-time
	 contention between threads. So, a reentrant function is always
	 thread-safe, but not vice versa.

	 Additionally there is a related attribute for functions named asyn‐
	 chronous-safe, which comes into play in conjunction with signal han‐
	 dlers. This is very related to the problem of reentrant functions. An
	 asynchronous-safe function is one that can be called safe and without
	 side-effects from within a signal handler context. Usually very few
	 functions are of this type, because an application is very restricted
	 in what it can perform from within a signal handler (especially what
	 system functions it is allowed to call). The reason mainly is,
	 because only a few system functions are officially declared by POSIX
	 as guaranteed to be asynchronous-safe. Asynchronous-safe functions
	 usually have to be already reentrant.

       User-Space Threads

       User-space threads can be implemented in various way. The two tradi‐
       tional approaches are:

       1. Matrix-based explicit dispatching between small units of execution:

	  Here the global procedures of the application are split into small
	  execution units (each is required to not run for more than a few
	  milliseconds) and those units are implemented by separate functions.
	  Then a global matrix is defined which describes the execution (and
	  perhaps even dependency) order of these functions. The main server
	  procedure then just dispatches between these units by calling one
	  function after each other controlled by this matrix. The threads are
	  created by more than one jump-trail through this matrix and by
	  switching between these jump-trails controlled by corresponding
	  occurred events.

	  This approach gives the best possible performance, because one can
	  fine-tune the threads of execution by adjusting the matrix, and the
	  scheduling is done explicitly by the application itself. It is also
	  very portable, because the matrix is just an ordinary data struc‐
	  ture, and functions are a standard feature of ANSI C.

	  The disadvantage of this approach is that it is complicated to write
	  large applications with this approach, because in those applications
	  one quickly gets hundreds(!) of execution units and the control flow
	  inside such an application is very hard to understand (because it is
	  interrupted by function borders and one always has to remember the
	  global dispatching matrix to follow it). Additionally, all threads
	  operate on the same execution stack. Although this saves memory, it
	  is often nasty, because one cannot switch between threads in the
	  middle of a function. Thus the scheduling borders are the function
	  borders.

       2. Context-based implicit scheduling between threads of execution:

	  Here the idea is that one programs the application as with forked
	  processes, i.e., one spawns a thread of execution and this runs from
	  the begin to the end without an interrupted control flow. But the
	  control flow can be still interrupted - even in the middle of a
	  function.  Actually in a preemptive way, similar to what the kernel
	  does for the heavy-weight processes, i.e., every few milliseconds
	  the user-space scheduler switches between the threads of execution.
	  But the thread itself doesn't recognize this and usually (except for
	  synchronization issues) doesn't have to care about this.

	  The advantage of this approach is that it's very easy to program,
	  because the control flow and context of a thread directly follows a
	  procedure without forced interrupts through function borders.	 Addi‐
	  tionally, the programming is very similar to a traditional and well
	  understood fork(2) based approach.

	  The disadvantage is that although the general performance is
	  increased, compared to using approaches based on heavy-weight pro‐
	  cesses, it is decreased compared to the matrix-approach above.
	  Because the implicit preemptive scheduling does usually a lot more
	  context switches (every user-space context switch costs some over‐
	  head even when it is a lot cheaper than a kernel-level context
	  switch) than the explicit cooperative/non-preemptive scheduling.
	  Finally, there is no really portable POSIX/ANSI-C based way to
	  implement user-space preemptive threading. Either the platform
	  already has threads, or one has to hope that some semi-portable
	  package exists for it. And even those semi-portable packages usually
	  have to deal with assembler code and other nasty internals and are
	  not easy to port to forthcoming platforms.

       So, in short: the matrix-dispatching approach is portable and fast, but
       nasty to program. The thread scheduling approach is easy to program,
       but suffers from synchronization and portability problems caused by its
       preemptive nature.

       The Compromise of Pth

       But why not combine the good aspects of both approaches while avoiding
       their bad aspects? That's the goal of Pth. Pth implements easy-to-pro‐
       gram threads of execution, but avoids the problems of preemptive sched‐
       uling by using non-preemptive scheduling instead.

       This sounds like, and is, a useful approach. Nevertheless, one has to
       keep the implications of non-preemptive thread scheduling in mind when
       working with Pth. The following list summarizes a few essential points:

       o Pth provides maximum portability, but NOT the fanciest features.

	 This is, because it uses a nifty and portable POSIX/ANSI-C approach
	 for thread creation (and this way doesn't require any platform depen‐
	 dent assembler hacks) and schedules the threads in non-preemptive way
	 (which doesn't require unportable facilities like "SIGVTALRM"). On
	 the other hand, this way not all fancy threading features can be
	 implemented.  Nevertheless the available facilities are enough to
	 provide a robust and full-featured threading system.

       o Pth increases the responsiveness and concurrency of an event-driven
	 application, but NOT the concurrency of number-crunching applica‐
	 tions.

	 The reason is the non-preemptive scheduling. Number-crunching appli‐
	 cations usually require preemptive scheduling to achieve concurrency
	 because of their long CPU bursts. For them, non-preemptive scheduling
	 (even together with explicit yielding) provides only the old concept
	 of `coroutines'. On the other hand, event driven applications benefit
	 greatly from non-preemptive scheduling. They have only short CPU
	 bursts and lots of events to wait on, and this way run faster under
	 non-preemptive scheduling because no unnecessary context switching
	 occurs, as it is the case for preemptive scheduling. That's why Pth
	 is mainly intended for server type applications, although there is no
	 technical restriction.

       o Pth requires thread-safe functions, but NOT reentrant functions.

	 This nice fact exists again because of the nature of non-preemptive
	 scheduling, where a function isn't interrupted and this way cannot be
	 reentered before it returned. This is a great portability benefit,
	 because thread-safety can be achieved more easily than reentrance
	 possibility. Especially this means that under Pth more existing
	 third-party libraries can be used without side-effects than it's the
	 case for other threading systems.

       o Pth doesn't require any kernel support, but can NOT benefit from mul‐
	 tiprocessor machines.

	 This means that Pth runs on almost all Unix kernels, because the ker‐
	 nel does not need to be aware of the Pth threads (because they are
	 implemented entirely in user-space). On the other hand, it cannot
	 benefit from the existence of multiprocessors, because for this, ker‐
	 nel support would be needed. In practice, this is no problem, because
	 multiprocessor systems are rare, and portability is almost more
	 important than highest concurrency.

       The life cycle of a thread

       To understand the Pth Application Programming Interface (API), it helps
       to first understand the life cycle of a thread in the Pth threading
       system. It can be illustrated with the following directed graph:

		    NEW
		     ⎪
		     V
	     +---> READY ---+
	     ⎪	     ^	    ⎪
	     ⎪	     ⎪	    V
	  WAITING <--+-- RUNNING
			    ⎪
	     :		    V
	  SUSPENDED	  DEAD

       When a new thread is created, it is moved into the NEW queue of the
       scheduler. On the next dispatching for this thread, the scheduler picks
       it up from there and moves it to the READY queue. This is a queue con‐
       taining all threads which want to perform a CPU burst. There they are
       queued in priority order. On each dispatching step, the scheduler
       always removes the thread with the highest priority only. It then
       increases the priority of all remaining threads by 1, to prevent them
       from `starving'.

       The thread which was removed from the READY queue is the new RUNNING
       thread (there is always just one RUNNING thread, of course). The RUN‐
       NING thread is assigned execution control. After this thread yields
       execution (either explicitly by yielding execution or implicitly by
       calling a function which would block) there are three possibilities:
       Either it has terminated, then it is moved to the DEAD queue, or it has
       events on which it wants to wait, then it is moved into the WAITING
       queue. Else it is assumed it wants to perform more CPU bursts and imme‐
       diately enters the READY queue again.

       Before the next thread is taken out of the READY queue, the WAITING
       queue is checked for pending events. If one or more events occurred,
       the threads that are waiting on them are immediately moved to the READY
       queue.

       The purpose of the NEW queue has to do with the fact that in Pth a
       thread never directly switches to another thread. A thread always
       yields execution to the scheduler and the scheduler dispatches to the
       next thread. So a freshly spawned thread has to be kept somewhere until
       the scheduler gets a chance to pick it up for scheduling. That is what
       the NEW queue is for.

       The purpose of the DEAD queue is to support thread joining. When a
       thread is marked to be unjoinable, it is directly kicked out of the
       system after it terminated. But when it is joinable, it enters the DEAD
       queue. There it remains until another thread joins it.

       Finally, there is a special separated queue named SUSPENDED, to where
       threads can be manually moved from the NEW, READY or WAITING queues by
       the application. The purpose of this special queue is to temporarily
       absorb suspended threads until they are again resumed by the applica‐
       tion. Suspended threads do not cost scheduling or event handling
       resources, because they are temporarily completely out of the sched‐
       uler's scope. If a thread is resumed, it is moved back to the queue
       from where it originally came and this way again enters the schedulers
       scope.

APPLICATION PROGRAMMING INTERFACE (API)
       In the following the Pth Application Programming Interface (API) is
       discussed in detail. With the knowledge given above, it should now be
       easy to understand how to program threads with this API. In good Unix
       tradition, Pth functions use special return values ("NULL" in pointer
       context, "FALSE" in boolean context and "-1" in integer context) to
       indicate an error condition and set (or pass through) the "errno" sys‐
       tem variable to pass more details about the error to the caller.

       Global Library Management

       The following functions act on the library as a whole.  They are used
       to initialize and shutdown the scheduler and fetch information from it.

       int pth_init(void);
	   This initializes the Pth library. It has to be the first Pth API
	   function call in an application, and is mandatory. It's usually
	   done at the begin of the main() function of the application. This
	   implicitly spawns the internal scheduler thread and transforms the
	   single execution unit of the current process into a thread (the
	   `main' thread). It returns "TRUE" on success and "FALSE" on error.

       int pth_kill(void);
	   This kills the Pth library. It should be the last Pth API function
	   call in an application, but is not really required. It's usually
	   done at the end of the main function of the application. At least,
	   it has to be called from within the main thread. It implicitly
	   kills all threads and transforms back the calling thread into the
	   single execution unit of the underlying process.  The usual way to
	   terminate a Pth application is either a simple `"pth_exit(0);"' in
	   the main thread (which waits for all other threads to terminate,
	   kills the threading system and then terminates the process) or a
	   `"pth_kill(); exit(0)"' (which immediately kills the threading sys‐
	   tem and terminates the process). The pth_kill() return immediately
	   with a return code of "FALSE" if it is not called from within the
	   main thread. Else it kills the threading system and returns "TRUE".

       long pth_ctrl(unsigned long query, ...);
	   This is a generalized query/control function for the Pth library.
	   The argument query is a bitmask formed out of one or more
	   "PTH_CTRL_"XXXX queries. Currently the following queries are sup‐
	   ported:

	   "PTH_CTRL_GETTHREADS"
	       This returns the total number of threads currently in exis‐
	       tence.  This query actually is formed out of the combination of
	       queries for threads in a particular state, i.e., the
	       "PTH_CTRL_GETTHREADS" query is equal to the OR-combination of
	       all the following specialized queries:

	       "PTH_CTRL_GETTHREADS_NEW" for the number of threads in the new
	       queue (threads created via pth_spawn(3) but still not scheduled
	       once), "PTH_CTRL_GETTHREADS_READY" for the number of threads in
	       the ready queue (threads who want to do CPU bursts),
	       "PTH_CTRL_GETTHREADS_RUNNING" for the number of running threads
	       (always just one thread!), "PTH_CTRL_GETTHREADS_WAITING" for
	       the number of threads in the waiting queue (threads waiting for
	       events), "PTH_CTRL_GETTHREADS_SUSPENDED" for the number of
	       threads in the suspended queue (threads waiting to be resumed)
	       and "PTH_CTRL_GETTHREADS_DEAD" for the number of threads in the
	       new queue (terminated threads waiting for a join).

	   "PTH_CTRL_GETAVLOAD"
	       This requires a second argument of type `"float *"' (pointer to
	       a floating point variable).  It stores a floating point value
	       describing the exponential averaged load of the scheduler in
	       this variable. The load is a function from the number of
	       threads in the ready queue of the schedulers dispatching unit.
	       So a load around 1.0 means there is only one ready thread (the
	       standard situation when the application has no high load). A
	       higher load value means there a more threads ready who want to
	       do CPU bursts. The average load value updates once per second
	       only. The return value for this query is always 0.

	   "PTH_CTRL_GETPRIO"
	       This requires a second argument of type `"pth_t"' which identi‐
	       fies a thread.  It returns the priority (ranging from
	       "PTH_PRIO_MIN" to "PTH_PRIO_MAX") of the given thread.

	   "PTH_CTRL_GETNAME"
	       This requires a second argument of type `"pth_t"' which identi‐
	       fies a thread. It returns the name of the given thread, i.e.,
	       the return value of pth_ctrl(3) should be casted to a `"char
	       *"'.

	   "PTH_CTRL_DUMPSTATE"
	       This requires a second argument of type `"FILE *"' to which a
	       summary of the internal Pth library state is written to. The
	       main information which is currently written out is the current
	       state of the thread pool.

	   "PTH_CTRL_FAVOURNEW"
	       This requires a second argument of type `"int"' which specified
	       whether the GNU Pth scheduler favours new threads on startup,
	       i.e., whether they are moved from the new queue to the top
	       (argument is "TRUE") or middle (argument is "FALSE") of the
	       ready queue. The default is to favour new threads to make sure
	       they do not starve already at startup, although this slightly
	       violates the strict priority based scheduling.

	   The function returns "-1" on error.

       long pth_version(void);
	   This function returns a hex-value `0xVRRTLL' which describes the
	   current Pth library version. V is the version, RR the revisions, LL
	   the level and T the type of the level (alphalevel=0, betalevel=1,
	   patchlevel=2, etc). For instance Pth version 1.0b1 is encoded as
	   0x100101.  The reason for this unusual mapping is that this way the
	   version number is steadily increasing. The same value is also
	   available under compile time as "PTH_VERSION".

       Thread Attribute Handling

       Attribute objects are used in Pth for two things: First
       stand-alone/unbound attribute objects are used to store attributes for
       to be spawned threads.  Bounded attribute objects are used to modify
       attributes of already existing threads. The following attribute fields
       exists in attribute objects:

       "PTH_ATTR_PRIO" (read-write) ["int"]
	   Thread Priority between "PTH_PRIO_MIN" and "PTH_PRIO_MAX".  The
	   default is "PTH_PRIO_STD".

       "PTH_ATTR_NAME" (read-write) ["char *"]
	   Name of thread (up to 40 characters are stored only), mainly for
	   debugging purposes.

       "PTH_ATTR_DISPATCHES" (read-write) ["int"]
	   In bounded attribute objects, this field is incremented every time
	   the context is switched to the associated thread.

       "PTH_ATTR_JOINABLE" (read-write> ["int"]
	   The thread detachment type, "TRUE" indicates a joinable thread,
	   "FALSE" indicates a detached thread. When a thread is detached,
	   after termination it is immediately kicked out of the system
	   instead of inserted into the dead queue.

       "PTH_ATTR_CANCEL_STATE" (read-write) ["unsigned int"]
	   The thread cancellation state, i.e., a combination of "PTH_CAN‐
	   CEL_ENABLE" or "PTH_CANCEL_DISABLE" and "PTH_CANCEL_DEFERRED" or
	   "PTH_CANCEL_ASYNCHRONOUS".

       "PTH_ATTR_STACK_SIZE" (read-write) ["unsigned int"]
	   The thread stack size in bytes. Use lower values than 64 KB with
	   great care!

       "PTH_ATTR_STACK_ADDR" (read-write) ["char *"]
	   A pointer to the lower address of a chunk of malloc(3)'ed memory
	   for the stack.

       "PTH_ATTR_TIME_SPAWN" (read-only) ["pth_time_t"]
	   The time when the thread was spawned.  This can be queried only
	   when the attribute object is bound to a thread.

       "PTH_ATTR_TIME_LAST" (read-only) ["pth_time_t"]
	   The time when the thread was last dispatched.  This can be queried
	   only when the attribute object is bound to a thread.

       "PTH_ATTR_TIME_RAN" (read-only) ["pth_time_t"]
	   The total time the thread was running.  This can be queried only
	   when the attribute object is bound to a thread.

       "PTH_ATTR_START_FUNC" (read-only) ["void *(*)(void *)"]
	   The thread start function.  This can be queried only when the
	   attribute object is bound to a thread.

       "PTH_ATTR_START_ARG" (read-only) ["void *"]
	   The thread start argument.  This can be queried only when the
	   attribute object is bound to a thread.

       "PTH_ATTR_STATE" (read-only) ["pth_state_t"]
	   The scheduling state of the thread, i.e., either "PTH_STATE_NEW",
	   "PTH_STATE_READY", "PTH_STATE_WAITING", or "PTH_STATE_DEAD" This
	   can be queried only when the attribute object is bound to a thread.

       "PTH_ATTR_EVENTS" (read-only) ["pth_event_t"]
	   The event ring the thread is waiting for.  This can be queried only
	   when the attribute object is bound to a thread.

       "PTH_ATTR_BOUND" (read-only) ["int"]
	   Whether the attribute object is bound ("TRUE") to a thread or not
	   ("FALSE").

       The following API functions can be used to handle the attribute
       objects:

       pth_attr_t pth_attr_of(pth_t tid);
	   This returns a new attribute object bound to thread tid.  Any
	   queries on this object directly fetch attributes from tid. And
	   attribute modifications directly change tid. Use such attribute
	   objects to modify existing threads.

       pth_attr_t pth_attr_new(void);
	   This returns a new unbound attribute object. An implicit
	   pth_attr_init() is done on it. Any queries on this object just
	   fetch stored attributes from it.  And attribute modifications just
	   change the stored attributes.  Use such attribute objects to pre-
	   configure attributes for to be spawned threads.

       int pth_attr_init(pth_attr_t attr);
	   This initializes an attribute object attr to the default values:
	   "PTH_ATTR_PRIO" := "PTH_PRIO_STD", "PTH_ATTR_NAME" := `"unknown"',
	   "PTH_ATTR_DISPATCHES" := 0, "PTH_ATTR_JOINABLE" := "TRUE",
	   "PTH_ATTR_CANCELSTATE" := "PTH_CANCEL_DEFAULT",
	   "PTH_ATTR_STACK_SIZE" := 64*1024 and "PTH_ATTR_STACK_ADDR" :=
	   "NULL". All other "PTH_ATTR_*" attributes are read-only attributes
	   and don't receive default values in attr, because they exists only
	   for bounded attribute objects.

       int pth_attr_set(pth_attr_t attr, int field, ...);
	   This sets the attribute field field in attr to a value specified as
	   an additional argument on the variable argument list. The following
	   attribute fields and argument pairs can be used:

	    PTH_ATTR_PRIO	    int
	    PTH_ATTR_NAME	    char *
	    PTH_ATTR_DISPATCHES	    int
	    PTH_ATTR_JOINABLE	    int
	    PTH_ATTR_CANCEL_STATE   unsigned int
	    PTH_ATTR_STACK_SIZE	    unsigned int
	    PTH_ATTR_STACK_ADDR	    char *

       int pth_attr_get(pth_attr_t attr, int field, ...);
	   This retrieves the attribute field field in attr and stores its
	   value in the variable specified through a pointer in an additional
	   argument on the variable argument list. The following fields and
	   argument pairs can be used:

	    PTH_ATTR_PRIO	    int *
	    PTH_ATTR_NAME	    char **
	    PTH_ATTR_DISPATCHES	    int *
	    PTH_ATTR_JOINABLE	    int *
	    PTH_ATTR_CANCEL_STATE   unsigned int *
	    PTH_ATTR_STACK_SIZE	    unsigned int *
	    PTH_ATTR_STACK_ADDR	    char **
	    PTH_ATTR_TIME_SPAWN	    pth_time_t *
	    PTH_ATTR_TIME_LAST	    pth_time_t *
	    PTH_ATTR_TIME_RAN	    pth_time_t *
	    PTH_ATTR_START_FUNC	    void *(**)(void *)
	    PTH_ATTR_START_ARG	    void **
	    PTH_ATTR_STATE	    pth_state_t *
	    PTH_ATTR_EVENTS	    pth_event_t *
	    PTH_ATTR_BOUND	    int *

       int pth_attr_destroy(pth_attr_t attr);
	   This destroys a attribute object attr. After this attr is no longer
	   a valid attribute object.

       Thread Control

       The following functions control the threading itself and make up the
       main API of the Pth library.

       pth_t pth_spawn(pth_attr_t attr, void *(*entry)(void *), void *arg);
	   This spawns a new thread with the attributes given in attr (or
	   "PTH_ATTR_DEFAULT" for default attributes - which means that thread
	   priority, joinability and cancel state are inherited from the cur‐
	   rent thread) with the starting point at routine entry; the dispatch
	   count is not inherited from the current thread if attr is not spec‐
	   ified - rather, it is initialized to zero.  This entry routine is
	   called as `pth_exit(entry(arg))' inside the new thread unit, i.e.,
	   entry's return value is fed to an implicit pth_exit(3). So the
	   thread can also exit by just returning. Nevertheless the thread can
	   also exit explicitly at any time by calling pth_exit(3). But keep
	   in mind that calling the POSIX function exit(3) still terminates
	   the complete process and not just the current thread.

	   There is no Pth-internal limit on the number of threads one can
	   spawn, except the limit implied by the available virtual memory.
	   Pth internally keeps track of thread in dynamic data structures.
	   The function returns "NULL" on error.

       int pth_once(pth_once_t *ctrlvar, void (*func)(void *), void *arg);
	   This is a convenience function which uses a control variable of
	   type "pth_once_t" to make sure a constructor function func is
	   called only once as `func(arg)' in the system. In other words: Only
	   the first call to pth_once(3) by any thread in the system succeeds.
	   The variable referenced via ctrlvar should be declared as
	   `"pth_once_t" variable-name = "PTH_ONCE_INIT";' before calling this
	   function.

       pth_t pth_self(void);
	   This just returns the unique thread handle of the currently running
	   thread.  This handle itself has to be treated as an opaque entity
	   by the application.	It's usually used as an argument to other
	   functions who require an argument of type "pth_t".

       int pth_suspend(pth_t tid);
	   This suspends a thread tid until it is manually resumed again via
	   pth_resume(3). For this, the thread is moved to the SUSPENDED queue
	   and this way is completely out of the scheduler's event handling
	   and thread dispatching scope. Suspending the current thread is not
	   allowed.  The function returns "TRUE" on success and "FALSE" on
	   errors.

       int pth_resume(pth_t tid);
	   This function resumes a previously suspended thread tid, i.e. tid
	   has to stay on the SUSPENDED queue. The thread is moved to the NEW,
	   READY or WAITING queue (dependent on what its state was when the
	   pth_suspend(3) call were made) and this way again enters the event
	   handling and thread dispatching scope of the scheduler. The func‐
	   tion returns "TRUE" on success and "FALSE" on errors.

       int pth_raise(pth_t tid, int sig)
	   This function raises a signal for delivery to thread tid only.
	   When one just raises a signal via raise(3) or kill(2), its deliv‐
	   ered to an arbitrary thread which has this signal not blocked.
	   With pth_raise(3) one can send a signal to a thread and its guaran‐
	   tees that only this thread gets the signal delivered. But keep in
	   mind that nevertheless the signals action is still configured
	   process-wide.  When sig is 0 plain thread checking is performed,
	   i.e., `"pth_raise(tid, 0)"' returns "TRUE" when thread tid still
	   exists in the PTH system but doesn't send any signal to it.

       int pth_yield(pth_t tid);
	   This explicitly yields back the execution control to the scheduler
	   thread.  Usually the execution is implicitly transferred back to
	   the scheduler when a thread waits for an event. But when a thread
	   has to do larger CPU bursts, it can be reasonable to interrupt it
	   explicitly by doing a few pth_yield(3) calls to give other threads
	   a chance to execute, too.  This obviously is the cooperating part
	   of Pth.  A thread has not to yield execution, of course. But when
	   you want to program a server application with good response times
	   the threads should be cooperative, i.e., when they should split
	   their CPU bursts into smaller units with this call.

	   Usually one specifies tid as "NULL" to indicate to the scheduler
	   that it can freely decide which thread to dispatch next.  But if
	   one wants to indicate to the scheduler that a particular thread
	   should be favored on the next dispatching step, one can specify
	   this thread explicitly. This allows the usage of the old concept of
	   coroutines where a thread/routine switches to a particular cooper‐
	   ating thread. If tid is not "NULL" and points to a new or ready
	   thread, it is guaranteed that this thread receives execution con‐
	   trol on the next dispatching step. If tid is in a different state
	   (that is, not in "PTH_STATE_NEW" or "PTH_STATE_READY") an error is
	   reported.

	   The function usually returns "TRUE" for success and only "FALSE"
	   (with "errno" set to "EINVAL") if tid specified an invalid or still
	   not new or ready thread.

       int pth_nap(pth_time_t naptime);
	   This functions suspends the execution of the current thread until
	   naptime is elapsed. naptime is of type "pth_time_t" and this way
	   has theoretically a resolution of one microsecond. In practice you
	   should neither rely on this nor that the thread is awakened exactly
	   after naptime has elapsed. It's only guarantees that the thread
	   will sleep at least naptime. But because of the non-preemptive
	   nature of Pth it can last longer (when another thread kept the CPU
	   for a long time). Additionally the resolution is dependent of the
	   implementation of timers by the operating system and these usually
	   have only a resolution of 10 microseconds or larger. But usually
	   this isn't important for an application unless it tries to use this
	   facility for real time tasks.

       int pth_wait(pth_event_t ev);
	   This is the link between the scheduler and the event facility (see
	   below for the various pth_event_xxx() functions). It's modeled like
	   select(2), i.e., one gives this function one or more events (in the
	   event ring specified by ev) on which the current thread wants to
	   wait. The scheduler awakes the thread when one ore more of them
	   occurred or failed after tagging them as such. The ev argument is a
	   pointer to an event ring which isn't changed except for the tag‐
	   ging. pth_wait(3) returns the number of occurred or failed events
	   and the application can use pth_event_status(3) to test which
	   events occurred or failed.

       int pth_cancel(pth_t tid);
	   This cancels a thread tid. How the cancellation is done depends on
	   the cancellation state of tid which the thread can configure
	   itself. When its state is "PTH_CANCEL_DISABLE" a cancellation
	   request is just made pending.  When it is "PTH_CANCEL_ENABLE" it
	   depends on the cancellation type what is performed. When its
	   "PTH_CANCEL_DEFERRED" again the cancellation request is just made
	   pending. But when its "PTH_CANCEL_ASYNCHRONOUS" the thread is imme‐
	   diately canceled before pth_cancel(3) returns. The effect of a
	   thread cancellation is equal to implicitly forcing the thread to
	   call `"pth_exit(PTH_CANCELED)"' at one of his cancellation points.
	   In Pth thread enter a cancellation point either explicitly via
	   pth_cancel_point(3) or implicitly by waiting for an event.

       int pth_abort(pth_t tid);
	   This is the cruel way to cancel a thread tid. When it's already
	   dead and waits to be joined it just joins it (via `"pth_join("tid",
	   NULL)"') and this way kicks it out of the system.  Else it forces
	   the thread to be not joinable and to allow asynchronous cancella‐
	   tion and then cancels it via `"pth_cancel("tid")"'.

       int pth_join(pth_t tid, void **value);
	   This joins the current thread with the thread specified via tid.
	   It first suspends the current thread until the tid thread has ter‐
	   minated. Then it is awakened and stores the value of tid's
	   pth_exit(3) call into *value (if value and not "NULL") and returns
	   to the caller. A thread can be joined only when it has the
	   attribute "PTH_ATTR_JOINABLE" set to "TRUE" (the default). A thread
	   can only be joined once, i.e., after the pth_join(3) call the
	   thread tid is completely removed from the system.

       void pth_exit(void *value);
	   This terminates the current thread. Whether it's immediately
	   removed from the system or inserted into the dead queue of the
	   scheduler depends on its join type which was specified at spawning
	   time. If it has the attribute "PTH_ATTR_JOINABLE" set to "FALSE",
	   it's immediately removed and value is ignored. Else the thread is
	   inserted into the dead queue and value remembered for a subsequent
	   pth_join(3) call by another thread.

       Utilities

       Utility functions.

       int pth_fdmode(int fd, int mode);
	   This switches the non-blocking mode flag on file descriptor fd.
	   The argument mode can be "PTH_FDMODE_BLOCK" for switching fd into
	   blocking I/O mode, "PTH_FDMODE_NONBLOCK" for switching fd into non-
	   blocking I/O mode or "PTH_FDMODE_POLL" for just polling the current
	   mode. The current mode is returned (either "PTH_FDMODE_BLOCK" or
	   "PTH_FDMODE_NONBLOCK") or "PTH_FDMODE_ERROR" on error. Keep in mind
	   that since Pth 1.1 there is no longer a requirement to manually
	   switch a file descriptor into non-blocking mode in order to use it.
	   This is automatically done temporarily inside Pth.  Instead when
	   you now switch a file descriptor explicitly into non-blocking mode,
	   pth_read(3) or pth_write(3) will never block the current thread.

       pth_time_t pth_time(long sec, long usec);
	   This is a constructor for a "pth_time_t" structure which is a con‐
	   venient function to avoid temporary structure values. It returns a
	   pth_time_t structure which holds the absolute time value specified
	   by sec and usec.

       pth_time_t pth_timeout(long sec, long usec);
	   This is a constructor for a "pth_time_t" structure which is a con‐
	   venient function to avoid temporary structure values.  It returns a
	   pth_time_t structure which holds the absolute time value calculated
	   by adding sec and usec to the current time.

       Sfdisc_t *pth_sfiodisc(void);
	   This functions is always available, but only reasonably usable when
	   Pth was built with Sfio support ("--with-sfio" option) and
	   "PTH_EXT_SFIO" is then defined by "pth.h". It is useful for appli‐
	   cations which want to use the comprehensive Sfio I/O library with
	   the Pth threading library. Then this function can be used to get an
	   Sfio discipline structure ("Sfdisc_t") which can be pushed onto
	   Sfio streams ("Sfio_t") in order to let this stream use
	   pth_read(3)/pth_write(2) instead of read(2)/write(2). The benefit
	   is that this way I/O on the Sfio stream does only block the current
	   thread instead of the whole process. The application has to free(3)
	   the "Sfdisc_t" structure when it is no longer needed. The Sfio
	   package can be found at http://www.research.att.com/sw/tools/sfio/.

       Cancellation Management

       Pth supports POSIX style thread cancellation via pth_cancel(3) and the
       following two related functions:

       void pth_cancel_state(int newstate, int *oldstate);
	   This manages the cancellation state of the current thread.  When
	   oldstate is not "NULL" the function stores the old cancellation
	   state under the variable pointed to by oldstate. When newstate is
	   not 0 it sets the new cancellation state. oldstate is created
	   before newstate is set.  A state is a combination of "PTH_CAN‐
	   CEL_ENABLE" or "PTH_CANCEL_DISABLE" and "PTH_CANCEL_DEFERRED" or
	   "PTH_CANCEL_ASYNCHRONOUS".  "PTH_CANCEL_ENABLE⎪PTH_CANCEL_DEFERRED"
	   (or "PTH_CANCEL_DEFAULT") is the default state where cancellation
	   is possible but only at cancellation points.	 Use "PTH_CANCEL_DIS‐
	   ABLE" to complete disable cancellation for a thread and "PTH_CAN‐
	   CEL_ASYNCHRONOUS" for allowing asynchronous cancellations, i.e.,
	   cancellations which can happen at any time.

       void pth_cancel_point(void);
	   This explicitly enter a cancellation point. When the current can‐
	   cellation state is "PTH_CANCEL_DISABLE" or no cancellation request
	   is pending, this has no side-effect and returns immediately. Else
	   it calls `"pth_exit(PTH_CANCELED)"'.

       Event Handling

       Pth has a very flexible event facility which is linked into the sched‐
       uler through the pth_wait(3) function. The following functions provide
       the handling of event rings.

       pth_event_t pth_event(unsigned long spec, ...);
	   This creates a new event ring consisting of a single initial event.
	   The type of the generated event is specified by spec. The following
	   types are available:

	   "PTH_EVENT_FD"
	       This is a file descriptor event. One or more of
	       "PTH_UNTIL_FD_READABLE", "PTH_UNTIL_FD_WRITEABLE" or
	       "PTH_UNTIL_FD_EXCEPTION" have to be OR-ed into spec to specify
	       on which state of the file descriptor you want to wait.	The
	       file descriptor itself has to be given as an additional argu‐
	       ment.  Example: `"pth_event(PTH_EVENT_FD⎪PTH_UNTIL_FD_READABLE,
	       fd)"'.

	   "PTH_EVENT_SELECT"
	       This is a multiple file descriptor event modeled directly after
	       the select(2) call (actually it is also used to implement
	       pth_select(3) internally).  It's a convenient way to wait for a
	       large set of file descriptors at once and at each file descrip‐
	       tor for a different type of state. Additionally as a nice side-
	       effect one receives the number of file descriptors which causes
	       the event to be occurred (using BSD semantics, i.e., when a
	       file descriptor occurred in two sets it's counted twice). The
	       arguments correspond directly to the select(2) function argu‐
	       ments except that there is no timeout argument (because time‐
	       outs already can be handled via "PTH_EVENT_TIME" events).

	       Example: `"pth_event(PTH_EVENT_SELECT, &rc, nfd, rfds, wfds,
	       efds)"' where "rc" has to be of type `"int *"', "nfd" has to be
	       of type `"int"' and "rfds", "wfds" and "efds" have to be of
	       type `"fd_set *"' (see select(2)). The number of occurred file
	       descriptors are stored in "rc".

	   "PTH_EVENT_SIGS"
	       This is a signal set event. The two additional arguments have
	       to be a pointer to a signal set (type `"sigset_t *"') and a
	       pointer to a signal number variable (type `"int *"').  This
	       event waits until one of the signals in the signal set
	       occurred.  As a result the occurred signal number is stored in
	       the second additional argument. Keep in mind that the Pth
	       scheduler doesn't block signals automatically.  So when you
	       want to wait for a signal with this event you've to block it
	       via sigprocmask(2) or it will be delivered without your notice.
	       Example: `"sigemptyset(&set); sigaddset(&set, SIGINT);
	       pth_event(PTH_EVENT_SIG, &set, &sig);"'.

	   "PTH_EVENT_TIME"
	       This is a time point event. The additional argument has to be
	       of type "pth_time_t" (usually on-the-fly generated via
	       pth_time(3)). This events waits until the specified time point
	       has elapsed. Keep in mind that the value is an absolute time
	       point and not an offset. When you want to wait for a specified
	       amount of time, you've to add the current time to the offset
	       (usually on-the-fly achieved via pth_timeout(3)).  Example:
	       `"pth_event(PTH_EVENT_TIME, pth_timeout(2,0))"'.

	   "PTH_EVENT_MSG"
	       This is a message port event. The additional argument has to be
	       of type "pth_msgport_t". This events waits until one or more
	       messages were received on the specified message port.  Example:
	       `"pth_event(PTH_EVENT_MSG, mp)"'.

	   "PTH_EVENT_TID"
	       This is a thread event. The additional argument has to be of
	       type "pth_t".  One of "PTH_UNTIL_TID_NEW",
	       "PTH_UNTIL_TID_READY", "PTH_UNTIL_TID_WAITING" or
	       "PTH_UNTIL_TID_DEAD" has to be OR-ed into spec to specify on
	       which state of the thread you want to wait.  Example:
	       `"pth_event(PTH_EVENT_TID⎪PTH_UNTIL_TID_DEAD, tid)"'.

	   "PTH_EVENT_FUNC"
	       This is a custom callback function event. Three additional
	       arguments have to be given with the following types: `"int
	       (*)(void *)"', `"void *"' and `"pth_time_t"'. The first is a
	       function pointer to a check function and the second argument is
	       a user-supplied context value which is passed to this function.
	       The scheduler calls this function on a regular basis (on his
	       own scheduler stack, so be very careful!) and the thread is
	       kept sleeping while the function returns "FALSE". Once it
	       returned "TRUE" the thread will be awakened. The check interval
	       is defined by the third argument, i.e., the check function is
	       polled again not until this amount of time elapsed. Example:
	       `"pth_event(PTH_EVENT_FUNC, func, arg, pth_time(0,500000))"'.

       unsigned long pth_event_typeof(pth_event_t ev);
	   This returns the type of event ev. It's a combination of the
	   describing "PTH_EVENT_XX" and "PTH_UNTIL_XX" value. This is espe‐
	   cially useful to know which arguments have to be supplied to the
	   pth_event_extract(3) function.

       int pth_event_extract(pth_event_t ev, ...);
	   When pth_event(3) is treated like sprintf(3), then this function is
	   sscanf(3), i.e., it is the inverse operation of pth_event(3). This
	   means that it can be used to extract the ingredients of an event.
	   The ingredients are stored into variables which are given as point‐
	   ers on the variable argument list.  Which pointers have to be
	   present depends on the event type and has to be determined by the
	   caller before via pth_event_typeof(3).

	   To make it clear, when you constructed ev via `"ev =
	   pth_event(PTH_EVENT_FD, fd);"' you have to extract it via
	   `"pth_event_extract(ev, &fd)"', etc. For multiple arguments of an
	   event the order of the pointer arguments is the same as for
	   pth_event(3). But always keep in mind that you have to always sup‐
	   ply pointers to variables and these variables have to be of the
	   same type as the argument of pth_event(3) required.

       pth_event_t pth_event_concat(pth_event_t ev, ...);
	   This concatenates one or more additional event rings to the event
	   ring ev and returns ev. The end of the argument list has to be
	   marked with a "NULL" argument. Use this function to create real
	   events rings out of the single-event rings created by pth_event(3).

       pth_event_t pth_event_isolate(pth_event_t ev);
	   This isolates the event ev from possibly appended events in the
	   event ring.	When in ev only one event exists, this returns "NULL".
	   When remaining events exists, they form a new event ring which is
	   returned.

       pth_event_t pth_event_walk(pth_event_t ev, int direction);
	   This walks to the next (when direction is "PTH_WALK_NEXT") or pre‐
	   views (when direction is "PTH_WALK_PREV") event in the event ring
	   ev and returns this new reached event. Additionally
	   "PTH_UNTIL_OCCURRED" can be OR-ed into direction to walk to the
	   next/previous occurred event in the ring ev.

       pth_status_t pth_event_status(pth_event_t ev);
	   This returns the status of event ev. This is a fast operation
	   because only a tag on ev is checked which was either set or still
	   not set by the scheduler. In other words: This doesn't check the
	   event itself, it just checks the last knowledge of the scheduler.
	   The possible returned status codes are: "PTH_STATUS_PENDING" (event
	   is still pending), "PTH_STATUS_OCCURRED" (event successfully
	   occurred), "PTH_STATUS_FAILED" (event failed).

       int pth_event_free(pth_event_t ev, int mode);
	   This deallocates the event ev (when mode is "PTH_FREE_THIS") or all
	   events appended to the event ring under ev (when mode is
	   "PTH_FREE_ALL").

       Key-Based Storage

       The following functions provide thread-local storage through unique
       keys similar to the POSIX Pthread API. Use this for thread specific
       global data.

       int pth_key_create(pth_key_t *key, void (*func)(void *));
	   This created a new unique key and stores it in key.	Additionally
	   func can specify a destructor function which is called on the cur‐
	   rent threads termination with the key.

       int pth_key_delete(pth_key_t key);
	   This explicitly destroys a key key.

       int pth_key_setdata(pth_key_t key, const void *value);
	   This stores value under key.

       void *pth_key_getdata(pth_key_t key);
	   This retrieves the value under key.

       Message Port Communication

       The following functions provide message ports which can be used for
       efficient and flexible inter-thread communication.

       pth_msgport_t pth_msgport_create(const char *name);
	   This returns a pointer to a new message port. If name name is not
	   "NULL", the name can be used by other threads via pth_msg‐
	   port_find(3) to find the message port in case they do not know
	   directly the pointer to the message port.

       void pth_msgport_destroy(pth_msgport_t mp);
	   This destroys a message port mp. Before all pending messages on it
	   are replied to their origin message port.

       pth_msgport_t pth_msgport_find(const char *name);
	   This finds a message port in the system by name and returns the
	   pointer to it.

       int pth_msgport_pending(pth_msgport_t mp);
	   This returns the number of pending messages on message port mp.

       int pth_msgport_put(pth_msgport_t mp, pth_message_t *m);
	   This puts (or sends) a message m to message port mp.

       pth_message_t *pth_msgport_get(pth_msgport_t mp);
	   This gets (or receives) the top message from message port mp.
	   Incoming messages are always kept in a queue, so there can be more
	   pending messages, of course.

       int pth_msgport_reply(pth_message_t *m);
	   This replies a message m to the message port of the sender.

       Thread Cleanups

       Per-thread cleanup functions.

       int pth_cleanup_push(void (*handler)(void *), void *arg);
	   This pushes the routine handler onto the stack of cleanup routines
	   for the current thread.  These routines are called in LIFO order
	   when the thread terminates.

       int pth_cleanup_pop(int execute);
	   This pops the top-most routine from the stack of cleanup routines
	   for the current thread. When execute is "TRUE" the routine is addi‐
	   tionally called.

       Process Forking

       The following functions provide some special support for process fork‐
       ing situations inside the threading environment.

       int pth_atfork_push(void (*prepare)(void *), void (*)(void *parent),
       void (*)(void *child), void *arg);
	   This function declares forking handlers to be called before and
	   after pth_fork(3), in the context of the thread that called
	   pth_fork(3). The prepare handler is called before fork(2) process‐
	   ing commences. The parent handler is called	 after fork(2) pro‐
	   cessing completes in the parent process.  The child handler is
	   called after fork(2) processing completed in the child process. If
	   no handling is desired at one or more of these three points, the
	   corresponding handler can be given as "NULL".  Each handler is
	   called with arg as the argument.

	   The order of calls to pth_atfork_push(3) is significant. The parent
	   and child handlers are called in the order in which they were
	   established by calls to pth_atfork_push(3), i.e., FIFO. The prepare
	   fork handlers are called in the opposite order, i.e., LIFO.

       int pth_atfork_pop(void);
	   This removes the top-most handlers on the forking handler stack
	   which were established with the last pth_atfork_push(3) call. It
	   returns "FALSE" when no more handlers couldn't be removed from the
	   stack.

       pid_t pth_fork(void);
	   This is a variant of fork(2) with the difference that the current
	   thread only is forked into a separate process, i.e., in the parent
	   process nothing changes while in the child process all threads are
	   gone except for the scheduler and the calling thread. When you
	   really want to duplicate all threads in the current process you
	   should use fork(2) directly. But this is usually not reasonable.
	   Additionally this function takes care of forking handlers as estab‐
	   lished by pth_fork_push(3).

       Synchronization

       The following functions provide synchronization support via mutual
       exclusion locks (mutex), read-write locks (rwlock), condition variables
       (cond) and barriers (barrier). Keep in mind that in a non-preemptive
       threading system like Pth this might sound unnecessary at the first
       look, because a thread isn't interrupted by the system. Actually when
       you have a critical code section which doesn't contain any pth_xxx()
       functions, you don't need any mutex to protect it, of course.

       But when your critical code section contains any pth_xxx() function the
       chance is high that these temporarily switch to the scheduler. And this
       way other threads can make progress and enter your critical code sec‐
       tion, too.  This is especially true for critical code sections which
       implicitly or explicitly use the event mechanism.

       int pth_mutex_init(pth_mutex_t *mutex);
	   This dynamically initializes a mutex variable of type
	   `"pth_mutex_t"'.  Alternatively one can also use static initializa‐
	   tion via `"pth_mutex_t mutex = PTH_MUTEX_INIT"'.

       int pth_mutex_acquire(pth_mutex_t *mutex, int try, pth_event_t ev);
	   This acquires a mutex mutex.	 If the mutex is already locked by
	   another thread, the current threads execution is suspended until
	   the mutex is unlocked again or additionally the extra events in ev
	   occurred (when ev is not "NULL").  Recursive locking is explicitly
	   supported, i.e., a thread is allowed to acquire a mutex more than
	   once before its released. But it then also has be released the same
	   number of times until the mutex is again lockable by others.	 When
	   try is "TRUE" this function never suspends execution. Instead it
	   returns "FALSE" with "errno" set to "EBUSY".

       int pth_mutex_release(pth_mutex_t *mutex);
	   This decrements the recursion locking count on mutex and when it is
	   zero it releases the mutex mutex.

       int pth_rwlock_init(pth_rwlock_t *rwlock);
	   This dynamically initializes a read-write lock variable of type
	   `"pth_rwlock_t"'.  Alternatively one can also use static initial‐
	   ization via `"pth_rwlock_t rwlock = PTH_RWLOCK_INIT"'.

       int pth_rwlock_acquire(pth_rwlock_t *rwlock, int op, int try,
       pth_event_t ev);
	   This acquires a read-only (when op is "PTH_RWLOCK_RD") or a read-
	   write (when op is "PTH_RWLOCK_RW") lock rwlock. When the lock is
	   only locked by other threads in read-only mode, the lock succeeds.
	   But when one thread holds a read-write lock, all locking attempts
	   suspend the current thread until this lock is released again. Addi‐
	   tionally in ev events can be given to let the locking timeout, etc.
	   When try is "TRUE" this function never suspends execution. Instead
	   it returns "FALSE" with "errno" set to "EBUSY".

       int pth_rwlock_release(pth_rwlock_t *rwlock);
	   This releases a previously acquired (read-only or read-write) lock.

       int pth_cond_init(pth_cond_t *cond);
	   This dynamically initializes a condition variable variable of type
	   `"pth_cond_t"'.  Alternatively one can also use static initializa‐
	   tion via `"pth_cond_t cond = PTH_COND_INIT"'.

       int pth_cond_await(pth_cond_t *cond, pth_mutex_t *mutex, pth_event_t
       ev);
	   This awaits a condition situation. The caller has to follow the
	   semantics of the POSIX condition variables: mutex has to be
	   acquired before this function is called. The execution of the cur‐
	   rent thread is then suspended either until the events in ev
	   occurred (when ev is not "NULL") or cond was notified by another
	   thread via pth_cond_notify(3).  While the thread is waiting, mutex
	   is released. Before it returns mutex is reacquired.

       int pth_cond_notify(pth_cond_t *cond, int broadcast);
	   This notified one or all threads which are waiting on cond.	When
	   broadcast is "TRUE" all thread are notified, else only a single
	   (unspecified) one.

       int pth_barrier_init(pth_barrier_t *barrier, int threshold);
	   This dynamically initializes a barrier variable of type `"pth_bar‐
	   rier_t"'.  Alternatively one can also use static initialization via
	   `"pth_barrier_t barrier = PTH_BARRIER_INIT("threadhold")"'.

       int pth_barrier_reach(pth_barrier_t *barrier);
	   This function reaches a barrier barrier. If this is the last thread
	   (as specified by threshold on init of barrier) all threads are
	   awakened.  Else the current thread is suspended until the last
	   thread reached the barrier and this way awakes all threads. The
	   function returns (beside "FALSE" on error) the value "TRUE" for any
	   thread which neither reached the barrier as the first nor the last
	   thread; "PTH_BARRIER_HEADLIGHT" for the thread which reached the
	   barrier as the first thread and "PTH_BARRIER_TAILLIGHT" for the
	   thread which reached the barrier as the last thread.

       User-Space Context

       The following functions provide a stand-alone sub-API for user-space
       context switching. It internally is based on the same underlying
       machine context switching mechanism the threads in GNU Pth are based
       on.  Hence these functions you can use for implementing your own simple
       user-space threads. The "pth_uctx_t" context is somewhat modeled after
       POSIX ucontext(3).

       The time required to create (via pth_uctx_make(3)) a user-space context
       can range from just a few microseconds up to a more dramatical time
       (depending on the machine context switching method which is available
       on the platform). On the other hand, the raw performance in switching
       the user-space contexts is always very good (nearly independent of the
       used machine context switching method). For instance, on an Intel Pen‐
       tium-III CPU with 800Mhz running under FreeBSD 4 one usually achieves
       about 260,000 user-space context switches (via pth_uctx_switch(3)) per
       second.

       int pth_uctx_create(pth_uctx_t *uctx);
	   This function creates a user-space context and stores it into uctx.
	   There is still no underlying user-space context configured. You
	   still have to do this with pth_uctx_make(3). On success, this func‐
	   tion returns "TRUE", else "FALSE".

       int pth_uctx_make(pth_uctx_t uctx, char *sk_addr, size_t sk_size, const
       sigset_t *sigmask, void (*start_func)(void *), void *start_arg,
       pth_uctx_t uctx_after);
	   This function makes a new user-space context in uctx which will
	   operate on the run-time stack sk_addr (which is of maximum size
	   sk_size), with the signals in sigmask blocked (if sigmask is not
	   "NULL") and starting to execute with the call
	   start_func(start_arg). If sk_addr is "NULL", a stack is dynamically
	   allocated. The stack size sk_size has to be at least 16384 (16KB).
	   If the start function start_func returns and uctx_after is not
	   "NULL", an implicit user-space context switch to this context is
	   performed. Else (if uctx_after is "NULL") the process is terminated
	   with exit(3). This function is somewhat modeled after POSIX make‐
	   context(3). On success, this function returns "TRUE", else "FALSE".

       int pth_uctx_switch(pth_uctx_t uctx_from, pth_uctx_t uctx_to);
	   This function saves the current user-space context in uctx_from for
	   later restoring by another call to pth_uctx_switch(3) and restores
	   the new user-space context from uctx_to, which previously had to be
	   set with either a previous call to pth_uctx_switch(3) or initially
	   by pth_uctx_make(3). This function is somewhat modeled after POSIX
	   swapcontext(3). If uctx_from or uctx_to are "NULL" or if uctx_to
	   contains no valid user-space context, "FALSE" is returned instead
	   of "TRUE". These are the only errors possible.

       int pth_uctx_destroy(pth_uctx_t uctx);
	   This function destroys the user-space context in uctx. The run-time
	   stack associated with the user-space context is deallocated only if
	   it was not given by the application (see sk_addr of pth_uctx_cre‐
	   ate(3)).  If uctx is "NULL", "FALSE" is returned instead of "TRUE".
	   This is the only error possible.

       Generalized POSIX Replacement API

       The following functions are generalized replacements functions for the
       POSIX API, i.e., they are similar to the functions under `Standard
       POSIX Replacement API' but all have an additional event argument which
       can be used for timeouts, etc.

       int pth_sigwait_ev(const sigset_t *set, int *sig, pth_event_t ev);
	   This is equal to pth_sigwait(3) (see below), but has an additional
	   event argument ev. When pth_sigwait(3) suspends the current threads
	   execution it usually only uses the signal event on set to awake.
	   With this function any number of extra events can be used to awake
	   the current thread (remember that ev actually is an event ring).

       int pth_connect_ev(int s, const struct sockaddr *addr, socklen_t
       addrlen, pth_event_t ev);
	   This is equal to pth_connect(3) (see below), but has an additional
	   event argument ev. When pth_connect(3) suspends the current threads
	   execution it usually only uses the I/O event on s to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       int pth_accept_ev(int s, struct sockaddr *addr, socklen_t *addrlen,
       pth_event_t ev);
	   This is equal to pth_accept(3) (see below), but has an additional
	   event argument ev. When pth_accept(3) suspends the current threads
	   execution it usually only uses the I/O event on s to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       int pth_select_ev(int nfd, fd_set *rfds, fd_set *wfds, fd_set *efds,
       struct timeval *timeout, pth_event_t ev);
	   This is equal to pth_select(3) (see below), but has an additional
	   event argument ev. When pth_select(3) suspends the current threads
	   execution it usually only uses the I/O event on rfds, wfds and efds
	   to awake. With this function any number of extra events can be used
	   to awake the current thread (remember that ev actually is an event
	   ring).

       int pth_poll_ev(struct pollfd *fds, unsigned int nfd, int timeout,
       pth_event_t ev);
	   This is equal to pth_poll(3) (see below), but has an additional
	   event argument ev. When pth_poll(3) suspends the current threads
	   execution it usually only uses the I/O event on fds to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_read_ev(int fd, void *buf, size_t nbytes, pth_event_t ev);
	   This is equal to pth_read(3) (see below), but has an additional
	   event argument ev. When pth_read(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_readv_ev(int fd, const struct iovec *iovec, int iovcnt,
       pth_event_t ev);
	   This is equal to pth_readv(3) (see below), but has an additional
	   event argument ev. When pth_readv(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_write_ev(int fd, const void *buf, size_t nbytes,
       pth_event_t ev);
	   This is equal to pth_write(3) (see below), but has an additional
	   event argument ev. When pth_write(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_writev_ev(int fd, const struct iovec *iovec, int iovcnt,
       pth_event_t ev);
	   This is equal to pth_writev(3) (see below), but has an additional
	   event argument ev. When pth_writev(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_recv_ev(int fd, void *buf, size_t nbytes, int flags,
       pth_event_t ev);
	   This is equal to pth_recv(3) (see below), but has an additional
	   event argument ev. When pth_recv(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_recvfrom_ev(int fd, void *buf, size_t nbytes, int flags,
       struct sockaddr *from, socklen_t *fromlen, pth_event_t ev);
	   This is equal to pth_recvfrom(3) (see below), but has an additional
	   event argument ev. When pth_recvfrom(3) suspends the current
	   threads execution it usually only uses the I/O event on fd to
	   awake. With this function any number of extra events can be used to
	   awake the current thread (remember that ev actually is an event
	   ring).

       ssize_t pth_send_ev(int fd, const void *buf, size_t nbytes, int flags,
       pth_event_t ev);
	   This is equal to pth_send(3) (see below), but has an additional
	   event argument ev. When pth_send(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       ssize_t pth_sendto_ev(int fd, const void *buf, size_t nbytes, int
       flags, const struct sockaddr *to, socklen_t tolen, pth_event_t ev);
	   This is equal to pth_sendto(3) (see below), but has an additional
	   event argument ev. When pth_sendto(3) suspends the current threads
	   execution it usually only uses the I/O event on fd to awake. With
	   this function any number of extra events can be used to awake the
	   current thread (remember that ev actually is an event ring).

       Standard POSIX Replacement API

       The following functions are standard replacements functions for the
       POSIX API.  The difference is mainly that they suspend the current
       thread only instead of the whole process in case the file descriptors
       will block.

       int pth_nanosleep(const struct timespec *rqtp, struct timespec *rmtp);
	   This is a variant of the POSIX nanosleep(3) function. It suspends
	   the current threads execution until the amount of time in rqtp
	   elapsed.  The thread is guaranteed to not wake up before this time,
	   but because of the non-preemptive scheduling nature of Pth, it can
	   be awakened later, of course. If rmtp is not "NULL", the "timespec"
	   structure it references is updated to contain the unslept amount
	   (the request time minus the time actually slept time). The differ‐
	   ence between nanosleep(3) and pth_nanosleep(3) is that that
	   pth_nanosleep(3) suspends only the execution of the current thread
	   and not the whole process.

       int pth_usleep(unsigned int usec);
	   This is a variant of the 4.3BSD usleep(3) function. It suspends the
	   current threads execution until usec microseconds (= usec*1/1000000
	   sec) elapsed.  The thread is guaranteed to not wake up before this
	   time, but because of the non-preemptive scheduling nature of Pth,
	   it can be awakened later, of course.	 The difference between
	   usleep(3) and pth_usleep(3) is that that pth_usleep(3) suspends
	   only the execution of the current thread and not the whole process.

       unsigned int pth_sleep(unsigned int sec);
	   This is a variant of the POSIX sleep(3) function. It suspends the
	   current threads execution until sec seconds elapsed.	 The thread is
	   guaranteed to not wake up before this time, but because of the non-
	   preemptive scheduling nature of Pth, it can be awakened later, of
	   course.  The difference between sleep(3) and pth_sleep(3) is that
	   pth_sleep(3) suspends only the execution of the current thread and
	   not the whole process.

       pid_t pth_waitpid(pid_t pid, int *status, int options);
	   This is a variant of the POSIX waitpid(2) function. It suspends the
	   current threads execution until status information is available for
	   a terminated child process pid.  The difference between waitpid(2)
	   and pth_waitpid(3) is that pth_waitpid(3) suspends only the execu‐
	   tion of the current thread and not the whole process.  For more
	   details about the arguments and return code semantics see wait‐
	   pid(2).

       int pth_system(const char *cmd);
	   This is a variant of the POSIX system(3) function. It executes the
	   shell command cmd with Bourne Shell ("sh") and suspends the current
	   threads execution until this command terminates. The difference
	   between system(3) and pth_system(3) is that pth_system(3) suspends
	   only the execution of the current thread and not the whole process.
	   For more details about the arguments and return code semantics see
	   system(3).

       int pth_sigmask(int how, const sigset_t *set, sigset_t *oset)
	   This is the Pth thread-related equivalent of POSIX sigprocmask(2)
	   respectively pthread_sigmask(3). The arguments how, set and oset
	   directly relate to sigprocmask(2), because Pth internally just uses
	   sigprocmask(2) here. So alternatively you can also directly call
	   sigprocmask(2), but for consistency reasons you should use this
	   function pth_sigmask(3).

       int pth_sigwait(const sigset_t *set, int *sig);
	   This is a variant of the POSIX.1c sigwait(3) function. It suspends
	   the current threads execution until a signal in set occurred and
	   stores the signal number in sig. The important point is that the
	   signal is not delivered to a signal handler. Instead it's caught by
	   the scheduler only in order to awake the pth_sigwait() call. The
	   trick and noticeable point here is that this way you get an asyn‐
	   chronous aware application that is written completely syn‐
	   chronously. When you think about the problem of asynchronous safe
	   functions you should recognize that this is a great benefit.

       int pth_connect(int s, const struct sockaddr *addr, socklen_t addrlen);
	   This is a variant of the 4.2BSD connect(2) function. It establishes
	   a connection on a socket s to target specified in addr and addrlen.
	   The difference between connect(2) and pth_connect(3) is that
	   pth_connect(3) suspends only the execution of the current thread
	   and not the whole process.  For more details about the arguments
	   and return code semantics see connect(2).

       int pth_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
	   This is a variant of the 4.2BSD accept(2) function. It accepts a
	   connection on a socket by extracting the first connection request
	   on the queue of pending connections, creating a new socket with the
	   same properties of s and allocates a new file descriptor for the
	   socket (which is returned).	The difference between accept(2) and
	   pth_accept(3) is that pth_accept(3) suspends only the execution of
	   the current thread and not the whole process.  For more details
	   about the arguments and return code semantics see accept(2).

       int pth_select(int nfd, fd_set *rfds, fd_set *wfds, fd_set *efds,
       struct timeval *timeout);
	   This is a variant of the 4.2BSD select(2) function.	It examines
	   the I/O descriptor sets whose addresses are passed in rfds, wfds,
	   and efds to see if some of their descriptors are ready for reading,
	   are ready for writing, or have an exceptional condition pending,
	   respectively.  For more details about the arguments and return code
	   semantics see select(2).

       int pth_pselect(int nfd, fd_set *rfds, fd_set *wfds, fd_set *efds,
       const struct timespec *timeout, const sigset_t *sigmask);
	   This is a variant of the POSIX pselect(2) function, which in turn
	   is a stronger variant of 4.2BSD select(2). The difference is that
	   the higher-resolution "struct timespec" is passed instead of the
	   lower-resolution "struct timeval" and that a signal mask is speci‐
	   fied which is temporarily set while waiting for input. For more
	   details about the arguments and return code semantics see pse‐
	   lect(2) and select(2).

       int pth_poll(struct pollfd *fds, unsigned int nfd, int timeout);
	   This is a variant of the SysV poll(2) function. It examines the I/O
	   descriptors which are passed in the array fds to see if some of
	   them are ready for reading, are ready for writing, or have an
	   exceptional condition pending, respectively. For more details about
	   the arguments and return code semantics see poll(2).

       ssize_t pth_read(int fd, void *buf, size_t nbytes);
	   This is a variant of the POSIX read(2) function. It reads up to
	   nbytes bytes into buf from file descriptor fd.  The difference
	   between read(2) and pth_read(2) is that pth_read(2) suspends execu‐
	   tion of the current thread until the file descriptor is ready for
	   reading. For more details about the arguments and return code
	   semantics see read(2).

       ssize_t pth_readv(int fd, const struct iovec *iovec, int iovcnt);
	   This is a variant of the POSIX readv(2) function. It reads data
	   from file descriptor fd into the first iovcnt rows of the iov vec‐
	   tor.	 The difference between readv(2) and pth_readv(2) is that
	   pth_readv(2) suspends execution of the current thread until the
	   file descriptor is ready for reading. For more details about the
	   arguments and return code semantics see readv(2).

       ssize_t pth_write(int fd, const void *buf, size_t nbytes);
	   This is a variant of the POSIX write(2) function. It writes nbytes
	   bytes from buf to file descriptor fd.  The difference between
	   write(2) and pth_write(2) is that pth_write(2) suspends execution
	   of the current thread until the file descriptor is ready for writ‐
	   ing.	 For more details about the arguments and return code seman‐
	   tics see write(2).

       ssize_t pth_writev(int fd, const struct iovec *iovec, int iovcnt);
	   This is a variant of the POSIX writev(2) function. It writes data
	   to file descriptor fd from the first iovcnt rows of the iov vector.
	   The difference between writev(2) and pth_writev(2) is that
	   pth_writev(2) suspends execution of the current thread until the
	   file descriptor is ready for reading. For more details about the
	   arguments and return code semantics see writev(2).

       ssize_t pth_pread(int fd, void *buf, size_t nbytes, off_t offset);
	   This is a variant of the POSIX pread(3) function.  It performs the
	   same action as a regular read(2), except that it reads from a given
	   position in the file without changing the file pointer.  The first
	   three arguments are the same as for pth_read(3) with the addition
	   of a fourth argument offset for the desired position inside the
	   file.

       ssize_t pth_pwrite(int fd, const void *buf, size_t nbytes, off_t off‐
       set);
	   This is a variant of the POSIX pwrite(3) function.  It performs the
	   same action as a regular write(2), except that it writes to a given
	   position in the file without changing the file pointer. The first
	   three arguments are the same as for pth_write(3) with the addition
	   of a fourth argument offset for the desired position inside the
	   file.

       ssize_t pth_recv(int fd, void *buf, size_t nbytes, int flags);
	   This is a variant of the SUSv2 recv(2) function and equal to
	   ``pth_recvfrom(fd, buf, nbytes, flags, NULL, 0)''.

       ssize_t pth_recvfrom(int fd, void *buf, size_t nbytes, int flags,
       struct sockaddr *from, socklen_t *fromlen);
	   This is a variant of the SUSv2 recvfrom(2) function. It reads up to
	   nbytes bytes into buf from file descriptor fd while using flags and
	   from/fromlen. The difference between recvfrom(2) and
	   pth_recvfrom(2) is that pth_recvfrom(2) suspends execution of the
	   current thread until the file descriptor is ready for reading. For
	   more details about the arguments and return code semantics see
	   recvfrom(2).

       ssize_t pth_send(int fd, const void *buf, size_t nbytes, int flags);
	   This is a variant of the SUSv2 send(2) function and equal to
	   ``pth_sendto(fd, buf, nbytes, flags, NULL, 0)''.

       ssize_t pth_sendto(int fd, const void *buf, size_t nbytes, int flags,
       const struct sockaddr *to, socklen_t tolen);
	   This is a variant of the SUSv2 sendto(2) function. It writes nbytes
	   bytes from buf to file descriptor fd while using flags and
	   to/tolen. The difference between sendto(2) and pth_sendto(2) is
	   that pth_sendto(2) suspends execution of the current thread until
	   the file descriptor is ready for writing. For more details about
	   the arguments and return code semantics see sendto(2).

EXAMPLE
       The following example is a useless server which does nothing more than
       listening on TCP port 12345 and displaying the current time to the
       socket when a connection was established. For each incoming connection
       a thread is spawned. Additionally, to see more multithreading, a use‐
       less ticker thread runs simultaneously which outputs the current time
       to "stderr" every 5 seconds. The example contains no error checking and
       is only intended to show you the look and feel of Pth.

	#include <stdio.h>
	#include <stdlib.h>
	#include <errno.h>
	#include <sys/types.h>
	#include <sys/socket.h>
	#include <netinet/in.h>
	#include <arpa/inet.h>
	#include <signal.h>
	#include <netdb.h>
	#include <unistd.h>
	#include "pth.h"

	#define PORT 12345

	/* the socket connection handler thread */
	static void *handler(void *_arg)
	{
	    int fd = (int)_arg;
	    time_t now;
	    char *ct;

	    now = time(NULL);
	    ct = ctime(&now);
	    pth_write(fd, ct, strlen(ct));
	    close(fd);
	    return NULL;
	}

	/* the stderr time ticker thread */
	static void *ticker(void *_arg)
	{
	    time_t now;
	    char *ct;
	    float load;

	    for (;;) {
		pth_sleep(5);
		now = time(NULL);
		ct = ctime(&now);
		ct[strlen(ct)-1] = '\0';
		pth_ctrl(PTH_CTRL_GETAVLOAD, &load);
		printf("ticker: time: %s, average load: %.2f\n", ct, load);
	    }
	}

	/* the main thread/procedure */
	int main(int argc, char *argv[])
	{
	    pth_attr_t attr;
	    struct sockaddr_in sar;
	    struct protoent *pe;
	    struct sockaddr_in peer_addr;
	    int peer_len;
	    int sa, sw;
	    int port;

	    pth_init();
	    signal(SIGPIPE, SIG_IGN);

	    attr = pth_attr_new();
	    pth_attr_set(attr, PTH_ATTR_NAME, "ticker");
	    pth_attr_set(attr, PTH_ATTR_STACK_SIZE, 64*1024);
	    pth_attr_set(attr, PTH_ATTR_JOINABLE, FALSE);
	    pth_spawn(attr, ticker, NULL);

	    pe = getprotobyname("tcp");
	    sa = socket(AF_INET, SOCK_STREAM, pe->p_proto);
	    sar.sin_family = AF_INET;
	    sar.sin_addr.s_addr = INADDR_ANY;
	    sar.sin_port = htons(PORT);
	    bind(sa, (struct sockaddr *)&sar, sizeof(struct sockaddr_in));
	    listen(sa, 10);

	    pth_attr_set(attr, PTH_ATTR_NAME, "handler");
	    for (;;) {
		peer_len = sizeof(peer_addr);
		sw = pth_accept(sa, (struct sockaddr *)&peer_addr, &peer_len);
		pth_spawn(attr, handler, (void *)sw);
	    }
	}

BUILD ENVIRONMENTS
       In this section we will discuss the canonical ways to establish the
       build environment for a Pth based program. The possibilities supported
       by Pth range from very simple environments to rather complex ones.

       Manual Build Environment (Novice)

       As a first example, assume we have the above test program staying in
       the source file "foo.c". Then we can create a very simple build envi‐
       ronment by just adding the following "Makefile":

	$ vi Makefile
	⎪ CC	  = cc
	⎪ CFLAGS  = `pth-config --cflags`
	⎪ LDFLAGS = `pth-config --ldflags`
	⎪ LIBS	  = `pth-config --libs`
	⎪
	⎪ all: foo
	⎪ foo: foo.o
	⎪     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
	⎪ foo.o: foo.c
	⎪     $(CC) $(CFLAGS) -c foo.c
	⎪ clean:
	⎪     rm -f foo foo.o

       This imports the necessary compiler and linker flags on-the-fly from
       the Pth installation via its "pth-config" program. This approach is
       straight-forward and works fine for small projects.

       Autoconf Build Environment (Advanced)

       The previous approach is simple but inflexible. First, to speed up
       building, it would be nice to not expand the compiler and linker flags
       every time the compiler is started. Second, it would be useful to also
       be able to build against uninstalled Pth, that is, against a Pth source
       tree which was just configured and built, but not installed. Third, it
       would be also useful to allow checking of the Pth version to make sure
       it is at least a minimum required version.  And finally, it would be
       also great to make sure Pth works correctly by first performing some
       sanity compile and run-time checks. All this can be done if we use GNU
       autoconf and the "AC_CHECK_PTH" macro provided by Pth. For this, we
       establish the following three files:

       First we again need the "Makefile", but this time it contains autoconf
       placeholders and additional cleanup targets. And we create it under the
       name "Makefile.in", because it is now an input file for autoconf:

	$ vi Makefile.in
	⎪ CC	  = @CC@
	⎪ CFLAGS  = @CFLAGS@
	⎪ LDFLAGS = @LDFLAGS@
	⎪ LIBS	  = @LIBS@
	⎪
	⎪ all: foo
	⎪ foo: foo.o
	⎪     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
	⎪ foo.o: foo.c
	⎪     $(CC) $(CFLAGS) -c foo.c
	⎪ clean:
	⎪     rm -f foo foo.o
	⎪ distclean:
	⎪     rm -f foo foo.o
	⎪     rm -f config.log config.status config.cache
	⎪     rm -f Makefile

       Because autoconf generates additional files, we added a canonical
       "distclean" target which cleans this up. Secondly, we wrote "config‐
       ure.ac", a (minimal) autoconf script specification:

	$ vi configure.ac
	⎪ AC_INIT(Makefile.in)
	⎪ AC_CHECK_PTH(1.3.0)
	⎪ AC_OUTPUT(Makefile)

       Then we let autoconf's "aclocal" program generate for us an "aclo‐
       cal.m4" file containing Pth's "AC_CHECK_PTH" macro. Then we generate
       the final "configure" script out of this "aclocal.m4" file and the
       "configure.ac" file:

	$ aclocal --acdir=`pth-config --acdir`
	$ autoconf

       After these steps, the working directory should look similar to this:

	$ ls -l
	-rw-r--r--  1 rse  users    176 Nov  3 11:11 Makefile.in
	-rw-r--r--  1 rse  users  15314 Nov  3 11:16 aclocal.m4
	-rwxr-xr-x  1 rse  users  52045 Nov  3 11:16 configure
	-rw-r--r--  1 rse  users     63 Nov  3 11:11 configure.ac
	-rw-r--r--  1 rse  users   4227 Nov  3 11:11 foo.c

       If we now run "configure" we get a correct "Makefile" which immediately
       can be used to build "foo" (assuming that Pth is already installed
       somewhere, so that "pth-config" is in $PATH):

	$ ./configure
	creating cache ./config.cache
	checking for gcc... gcc
	checking whether the C compiler (gcc   ) works... yes
	checking whether the C compiler (gcc   ) is a cross-compiler... no
	checking whether we are using GNU C... yes
	checking whether gcc accepts -g... yes
	checking how to run the C preprocessor... gcc -E
	checking for GNU Pth... version 1.3.0, installed under /usr/local
	updating cache ./config.cache
	creating ./config.status
	creating Makefile
	rse@en1:/e/gnu/pth/ac
	$ make
	gcc -g -O2 -I/usr/local/include -c foo.c
	gcc -L/usr/local/lib -o foo foo.o -lpth

       If Pth is installed in non-standard locations or "pth-config" is not in
       $PATH, one just has to drop the "configure" script a note about the
       location by running "configure" with the option "--with-pth="dir (where
       dir is the argument which was used with the "--prefix" option when Pth
       was installed).

       Autoconf Build Environment with Local Copy of Pth (Expert)

       Finally let us assume the "foo" program stays under either a GPL or
       LGPL distribution license and we want to make it a stand-alone package
       for easier distribution and installation.  That is, we don't want to
       oblige the end-user to install Pth just to allow our "foo" package to
       compile. For this, it is a convenient practice to include the required
       libraries (here Pth) into the source tree of the package (here "foo").
       Pth ships with all necessary support to allow us to easily achieve this
       approach. Say, we want Pth in a subdirectory named "pth/" and this
       directory should be seamlessly integrated into the configuration and
       build process of "foo".

       First we again start with the "Makefile.in", but this time it is a more
       advanced version which supports subdirectory movement:

	$ vi Makefile.in
	⎪ CC	  = @CC@
	⎪ CFLAGS  = @CFLAGS@
	⎪ LDFLAGS = @LDFLAGS@
	⎪ LIBS	  = @LIBS@
	⎪
	⎪ SUBDIRS = pth
	⎪
	⎪ all: subdirs_all foo
	⎪
	⎪ subdirs_all:
	⎪     @$(MAKE) $(MFLAGS) subdirs TARGET=all
	⎪ subdirs_clean:
	⎪     @$(MAKE) $(MFLAGS) subdirs TARGET=clean
	⎪ subdirs_distclean:
	⎪     @$(MAKE) $(MFLAGS) subdirs TARGET=distclean
	⎪ subdirs:
	⎪     @for subdir in $(SUBDIRS); do \
	⎪	  echo "===> $$subdir ($(TARGET))"; \
	⎪	  (cd $$subdir; $(MAKE) $(MFLAGS) $(TARGET) ⎪⎪ exit 1) ⎪⎪ exit 1; \
	⎪	  echo "<=== $$subdir"; \
	⎪     done
	⎪
	⎪ foo: foo.o
	⎪     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
	⎪ foo.o: foo.c
	⎪     $(CC) $(CFLAGS) -c foo.c
	⎪
	⎪ clean: subdirs_clean
	⎪     rm -f foo foo.o
	⎪ distclean: subdirs_distclean
	⎪     rm -f foo foo.o
	⎪     rm -f config.log config.status config.cache
	⎪     rm -f Makefile

       Then we create a slightly different autoconf script "configure.ac":

	$ vi configure.ac
	⎪ AC_INIT(Makefile.in)
	⎪ AC_CONFIG_AUX_DIR(pth)
	⎪ AC_CHECK_PTH(1.3.0, subdir:pth --disable-tests)
	⎪ AC_CONFIG_SUBDIRS(pth)AC_OUTPUT(Makefile)

       Here we provided a default value for "foo"'s "--with-pth" option as the
       second argument to "AC_CHECK_PTH" which indicates that Pth can be found
       in the subdirectory named "pth/". Additionally we specified that the
       "--disable-tests" option of Pth should be passed to the "pth/" subdi‐
       rectory, because we need only to build the Pth library itself. And we
       added a "AC_CONFIG_SUBDIR" call which indicates to autoconf that it
       should configure the "pth/" subdirectory, too. The "AC_CONFIG_AUX_DIR"
       directive was added just to make autoconf happy, because it wants to
       find a "install.sh" or "shtool" script if "AC_CONFIG_SUBDIRS" is used.

       Now we let autoconf's "aclocal" program again generate for us an "aclo‐
       cal.m4" file with the contents of Pth's "AC_CHECK_PTH" macro.  Finally
       we generate the "configure" script out of this "aclocal.m4" file and
       the "configure.ac" file.

	$ aclocal --acdir=`pth-config --acdir`
	$ autoconf

       Now we have to create the "pth/" subdirectory itself. For this, we
       extract the Pth distribution to the "foo" source tree and just rename
       it to "pth/":

	$ gunzip <pth-X.Y.Z.tar.gz ⎪ tar xvf -
	$ mv pth-X.Y.Z pth

       Optionally to reduce the size of the "pth/" subdirectory, we can strip
       down the Pth sources to a minimum with the striptease feature:

	$ cd pth
	$ ./configure
	$ make striptease
	$ cd ..

       After this the source tree of "foo" should look similar to this:

	$ ls -l
	-rw-r--r--  1 rse  users    709 Nov  3 11:51 Makefile.in
	-rw-r--r--  1 rse  users  16431 Nov  3 12:20 aclocal.m4
	-rwxr-xr-x  1 rse  users  57403 Nov  3 12:21 configure
	-rw-r--r--  1 rse  users    129 Nov  3 12:21 configure.ac
	-rw-r--r--  1 rse  users   4227 Nov  3 11:11 foo.c
	drwxr-xr-x  2 rse  users   3584 Nov  3 12:36 pth
	$ ls -l pth/
	-rw-rw-r--  1 rse  users   26344 Nov  1 20:12 COPYING
	-rw-rw-r--  1 rse  users    2042 Nov  3 12:36 Makefile.in
	-rw-rw-r--  1 rse  users    3967 Nov  1 19:48 README
	-rw-rw-r--  1 rse  users     340 Nov  3 12:36 README.1st
	-rw-rw-r--  1 rse  users   28719 Oct 31 17:06 config.guess
	-rw-rw-r--  1 rse  users   24274 Aug 18 13:31 config.sub
	-rwxrwxr-x  1 rse  users  155141 Nov  3 12:36 configure
	-rw-rw-r--  1 rse  users  162021 Nov  3 12:36 pth.c
	-rw-rw-r--  1 rse  users   18687 Nov  2 15:19 pth.h.in
	-rw-rw-r--  1 rse  users    5251 Oct 31 12:46 pth_acdef.h.in
	-rw-rw-r--  1 rse  users    2120 Nov  1 11:27 pth_acmac.h.in
	-rw-rw-r--  1 rse  users    2323 Nov  1 11:27 pth_p.h.in
	-rw-rw-r--  1 rse  users     946 Nov  1 11:27 pth_vers.c
	-rw-rw-r--  1 rse  users   26848 Nov  1 11:27 pthread.c
	-rw-rw-r--  1 rse  users   18772 Nov  1 11:27 pthread.h.in
	-rwxrwxr-x  1 rse  users   26188 Nov  3 12:36 shtool

       Now when we configure and build the "foo" package it looks similar to
       this:

	$ ./configure
	creating cache ./config.cache
	checking for gcc... gcc
	checking whether the C compiler (gcc   ) works... yes
	checking whether the C compiler (gcc   ) is a cross-compiler... no
	checking whether we are using GNU C... yes
	checking whether gcc accepts -g... yes
	checking how to run the C preprocessor... gcc -E
	checking for GNU Pth... version 1.3.0, local under pth
	updating cache ./config.cache
	creating ./config.status
	creating Makefile
	configuring in pth
	running /bin/sh ./configure  --enable-subdir --enable-batch
	--disable-tests --cache-file=.././config.cache --srcdir=.
	loading cache .././config.cache
	checking for gcc... (cached) gcc
	checking whether the C compiler (gcc   ) works... yes
	checking whether the C compiler (gcc   ) is a cross-compiler... no
	[...]
	$ make
	===> pth (all)
	./shtool scpp -o pth_p.h -t pth_p.h.in -Dcpp -Cintern -M '==#==' pth.c
	pth_vers.c
	gcc -c -I. -O2 -pipe pth.c
	gcc -c -I. -O2 -pipe pth_vers.c
	ar rc libpth.a pth.o pth_vers.o
	ranlib libpth.a
	<=== pth
	gcc -g -O2 -Ipth -c foo.c
	gcc -Lpth -o foo foo.o -lpth

       As you can see, autoconf now automatically configures the local
       (stripped down) copy of Pth in the subdirectory "pth/" and the "Make‐
       file" automatically builds the subdirectory, too.

SYSTEM CALL WRAPPER FACILITY
       Pth per default uses an explicit API, including the system calls. For
       instance you've to explicitly use pth_read(3) when you need a thread-
       aware read(3) and cannot expect that by just calling read(3) only the
       current thread is blocked. Instead with the standard read(3) call the
       whole process will be blocked. But because for some applications
       (mainly those consisting of lots of third-party stuff) this can be
       inconvenient.  Here it's required that a call to read(3) `magically'
       means pth_read(3). The problem here is that such magic Pth cannot pro‐
       vide per default because it's not really portable.  Nevertheless Pth
       provides a two step approach to solve this problem:

       Soft System Call Mapping

       This variant is available on all platforms and can always be enabled by
       building Pth with "--enable-syscall-soft". This then triggers some
       "#define"'s in the "pth.h" header which map for instance read(3) to
       pth_read(3), etc. Currently the following functions are mapped:
       fork(2), nanosleep(3), usleep(3), sleep(3), sigwait(3), waitpid(2),
       system(3), select(2), poll(2), connect(2), accept(2), read(2),
       write(2), recv(2), send(2), recvfrom(2), sendto(2).

       The drawback of this approach is just that really all source files of
       the application where these function calls occur have to include
       "pth.h", of course. And this also means that existing libraries,
       including the vendor's stdio, usually will still block the whole
       process if one of its I/O functions block.

       Hard System Call Mapping

       This variant is available only on those platforms where the syscall(2)
       function exists and there it can be enabled by building Pth with
       "--enable-syscall-hard". This then builds wrapper functions (for
       instances read(3)) into the Pth library which internally call the real
       Pth replacement functions (pth_read(3)). Currently the following func‐
       tions are mapped: fork(2), nanosleep(3), usleep(3), sleep(3), wait‐
       pid(2), system(3), select(2), poll(2), connect(2), accept(2), read(2),
       write(2).

       The drawback of this approach is that it depends on syscall(2) inter‐
       face and prototype conflicts can occur while building the wrapper func‐
       tions due to different function signatures in the vendor C header
       files.  But the advantage of this mapping variant is that the source
       files of the application where these function calls occur have not to
       include "pth.h" and that existing libraries, including the vendor's
       stdio, magically become thread-aware (and then block only the current
       thread).

IMPLEMENTATION NOTES
       Pth is very portable because it has only one part which perhaps has to
       be ported to new platforms (the machine context initialization). But it
       is written in a way which works on mostly all Unix platforms which sup‐
       port makecontext(2) or at least sigstack(2) or sigaltstack(2) [see
       "pth_mctx.c" for details]. Any other Pth code is POSIX and ANSI C based
       only.

       The context switching is done via either SUSv2 makecontext(2) or POSIX
       make[sig]setjmp(3) and [sig]longjmp(3). Here all CPU registers, the
       program counter and the stack pointer are switched. Additionally the
       Pth dispatcher switches also the global Unix "errno" variable [see
       "pth_mctx.c" for details] and the signal mask (either implicitly via
       sigsetjmp(3) or in an emulated way via explicit setprocmask(2) calls).

       The Pth event manager is mainly select(2) and gettimeofday(2) based,
       i.e., the current time is fetched via gettimeofday(2) once per context
       switch for time calculations and all I/O events are implemented via a
       single central select(2) call [see "pth_sched.c" for details].

       The thread control block management is done via virtual priority queues
       without any additional data structure overhead. For this, the queue
       linkage attributes are part of the thread control blocks and the queues
       are actually implemented as rings with a selected element as the entry
       point [see "pth_tcb.h" and "pth_pqueue.c" for details].

       Most time critical code sections (especially the dispatcher and event
       manager) are speeded up by inline functions (implemented as ANSI C pre-
       processor macros). Additionally any debugging code is completely
       removed from the source when not built with "-DPTH_DEBUG" (see Autoconf
       "--enable-debug" option), i.e., not only stub functions remain [see
       "pth_debug.c" for details].

RESTRICTIONS
       Pth (intentionally) provides no replacements for non-thread-safe func‐
       tions (like strtok(3) which uses a static internal buffer) or synchro‐
       nous system functions (like gethostbyname(3) which doesn't provide an
       asynchronous mode where it doesn't block). When you want to use those
       functions in your server application together with threads, you've to
       either link the application against special third-party libraries (or
       for thread-safe/reentrant functions possibly against an existing
       "libc_r" of the platform vendor). For an asynchronous DNS resolver
       library use the GNU adns package from Ian Jackson ( see
       http://www.gnu.org/software/adns/adns.html ).

HISTORY
       The Pth library was designed and implemented between February and July
       1999 by Ralf S. Engelschall after evaluating numerous (mostly preemp‐
       tive) thread libraries and after intensive discussions with Peter
       Simons, Martin Kraemer, Lars Eilebrecht and Ralph Babel related to an
       experimental (matrix based) non-preemptive C++ scheduler class written
       by Peter Simons.

       Pth was then implemented in order to combine the non-preemptive
       approach of multithreading (which provides better portability and per‐
       formance) with an API similar to the popular one found in Pthread
       libraries (which provides easy programming).

       So the essential idea of the non-preemptive approach was taken over
       from Peter Simons scheduler. The priority based scheduling algorithm
       was suggested by Martin Kraemer. Some code inspiration also came from
       an experimental threading library (rsthreads) written by Robert S. Thau
       for an ancient internal test version of the Apache webserver.  The con‐
       cept and API of message ports was borrowed from AmigaOS' Exec subsys‐
       tem. The concept and idea for the flexible event mechanism came from
       Paul Vixie's eventlib (which can be found as a part of BIND v8).

BUG REPORTS AND SUPPORT
       If you think you have found a bug in Pth, you should send a report as
       complete as possible to bug-pth@gnu.org. If you can, please try to fix
       the problem and include a patch, made with '"diff -u3"', in your
       report. Always, at least, include a reasonable amount of description in
       your report to allow the author to deterministically reproduce the bug.

       For further support you additionally can subscribe to the
       pth-users@gnu.org mailing list by sending an Email to
       pth-users-request@gnu.org with `"subscribe pth-users"' (or `"subscribe
       pth-users" address' if you want to subscribe from a particular Email
       address) in the body. Then you can discuss your issues with other Pth
       users by sending messages to pth-users@gnu.org. Currently (as of August
       2000) you can reach about 110 Pth users on this mailing list. Old post‐
       ings you can find at http://www.mail-archive.com/pth-users@gnu.org/.

SEE ALSO
       Related Web Locations

       `comp.programming.threads Newsgroup Archive', http://www.deja.com/top‐
       ics_if.xp?  search=topic&group=comp.programming.threads

       `comp.programming.threads Frequently Asked Questions (F.A.Q.)',
       http://www.lambdacs.com/newsgroup/FAQ.html

       `Multithreading - Definitions and Guidelines', Numeric Quest Inc 1998;
       http://www.numeric-quest.com/lang/multi-frame.html

       `The Single UNIX Specification, Version 2 - Threads', The Open Group
       1997; http://www.opengroup.org/onlinepubs /007908799/xsh/threads.html

       SMI Thread Resources, Sun Microsystems Inc; http://www.sun.com/work‐
       shop/threads/

       Bibliography on threads and multithreading, Torsten Amundsen;
       http://liinwww.ira.uka.de/bibliography/Os/threads.html

       Related Books

       B. Nichols, D. Buttlar, J.P. Farrel: `Pthreads Programming - A POSIX
       Standard for Better Multiprocessing', O'Reilly 1996; ISBN 1-56592-115-1

       B. Lewis, D. J. Berg: `Multithreaded Programming with Pthreads', Sun
       Microsystems Press, Prentice Hall 1998; ISBN 0-13-680729-1

       B. Lewis, D. J. Berg: `Threads Primer - A Guide To Multithreaded Pro‐
       gramming', Prentice Hall 1996; ISBN 0-13-443698-9

       S. J. Norton, M. D. Dipasquale: `Thread Time - The Multithreaded Pro‐
       gramming Guide', Prentice Hall 1997; ISBN 0-13-190067-6

       D. R. Butenhof: `Programming with POSIX Threads', Addison Wesley 1997;
       ISBN 0-201-63392-2

       Related Manpages

       pth-config(1), pthread(3).

       getcontext(2), setcontext(2), makecontext(2), swapcontext(2),
       sigstack(2), sigaltstack(2), sigaction(2), sigemptyset(2),
       sigaddset(2), sigprocmask(2), sigsuspend(2), sigsetjmp(3), sig‐
       longjmp(3), setjmp(3), longjmp(3), select(2), gettimeofday(2).

AUTHOR
	Ralf S. Engelschall
	rse@engelschall.com
	www.engelschall.com

08-Jun-2006			 GNU Pth 2.0.7				pth(3)
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