DCE_THREADS, Application Routines, pthread_setscheduler
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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/sys$common/syshlp/helplib.hlb DCE_THREADS, Application Routines, pthread_setscheduler *Conan The Librarian (sorry for the slow response - running on an old VAX) |
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NAME
pthread_setscheduler - Changes the current scheduling policy
and priority of a thread
SYNOPSIS
#include <pthread.h>
int pthread_setscheduler( pthread_t thread,
int scheduler,
int priority );
PARAMETERS
thread Thread whose scheduling policy is to be
changed.
scheduler New scheduling policy value for the thread
specified in thread. Valid values are as
follows:
SCHED_FIFO (First In, First Out)
The highest-priority thread runs
until it blocks. If there is more
than one thread with the same
priority, and that priority is the
highest among other threads, the
first thread to begin running
continues until it blocks.
SCHED_RR (Round Robin)
The highest-priority thread runs
until it blocks; however, threads
of equal priority, if that priority
is the highest among other threads,
are timesliced. Timeslicing is a
process in which threads alternate
using available processors.
SCHED_OTHER (Default)
All threads are timesliced.
SCHED_OTHER ensures that all
threads, regardless of priority,
receive some scheduling, and thus
no thread is completely denied
execution time. (However, SCHED_OTHER
threads can be denied execution time
by SCHED_FIFO or SCHED_RR threads.)
SCHED_FG_NP (Foreground)
Same as SCHED_OTHER. Threads are
timesliced and priorities can be
modified dynamically by the scheduler
to ensure fairness.
SCHED_BG_NP (Background)
Like SCHED_OTHER, ensures that all
threads, regardless of priority,
receive some scheduling. However,
SCHED_BG_NP can be denied execution
by any of the other scheduling
policies.
priority New priority value of the thread specified in
thread. The priority attribute depends on
scheduling policy. Valid values fall within
one of the following ranges:
o PRI_OTHER_MIN <= priority <= PRI_OTHER_MAX
o PRI_FIFO_MIN <= priority <= PRI_FIFO_MAX
o PRI_RR_MIN <= priority <= PRI_RR_MAX
o PRI_FG_MIN_NP <= priority <= PRI_FG_MAX_NP
o PRI_BG_MIN_NP <= priority <= PRI_BG_MAX_NP
If you create a new thread without specifying a threads attributes
object that contains a changed priority attribute, the default priority
of the newly created thread is the midpoint between PRI_OTHER_MIN and
PRI_OTHER_MAX (the midpoint between the minimum and the maximum for the
SCHED_OTHER policy).
When you call this routine to specify a minimum or maximum priority, use
the appropriate symbol; for example, PRI_FIFO_MIN or PRI_FIFO_MAX. To
specify a value between the minimum and maximum, use an appropriate
arithmetic expression. For example, to specify a priority midway between
the minimum and maximum for the Round Robin scheduling policy, specify
the following concept using your programming language's syntax:
pri_rr_mid = (PRI_RR_MIN + PRI_RR_MAX)/2
If your expression results in a value outside the range of minimum to
maximum, an error results when you use it.
DESCRIPTION
The pthread_setscheduler() routine changes the current scheduling policy
and priority of a thread. Call this routine to change both the priority
and scheduling policy of a thread at the same time. To change only the
priority, call the pthread_setprio() routine.
A thread changes its own scheduling policy and priority by using the
identifier returned by pthread_self(). Changing the scheduling policy
or priority, or both, of a thread can cause it to start executing or to
be preempted by another thread.
This routine differs from pthread_attr_setprio() and
pthread_attr_setsched() because those routines set the priority and
scheduling policy attributes that are used to establish the priority and
scheduling policy of a new thread when it is created. This routine, how-
ever, changes the priority and scheduling policy of an existing thread.
RETURN VALUES
If the function fails, errno may be set to one of the following values:
Return Error Description
______________________________________________________________
0 Successful completion.
-1 [EINVAL] The value specified by thread is invalid.
-1 [ENOTSUP] An attempt is made to set the policy to
an unsupported value.
-1 [ESRCH] The value specified by thread does not
refer to an existing thread.
-1 [EPERM] The caller does not have the appropriate
privileges to set the priority of the
specified thread.
RELATED INFORMATION
FUNCTIONS: pthread_attr_setprio
pthread_attr_setsched
pthread_create
pthread_self
pthread_setprio
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