SIGWAIT(2)SIGWAIT(2)NAMEsigwait - wait until a signal is posted
SYNOPSIS
#include <signal.h>
int sigwait(sigset_t *set);
Standard conforming
cc [ flag ... ] file ... -D_POSIX_PTHREAD_SEMANTICS [ library...]
#include <signal.h>
int sigwait(const sigset_t *set, int *sig);
DESCRIPTION
The sigwait() function selects a signal in set that is pending on the
calling thread. If no signal in set is pending, sigwait() blocks until
a signal in set becomes pending. The selected signal is cleared from
the set of signals pending on the calling thread and the number of the
signal is returned, or in the standard-conforming version (see stan‐
dards(5)) placed in sig. The selection of a signal in set is indepen‐
dent of the signal mask of the calling thread. This means a thread can
synchronously wait for signals that are being blocked by the signal
mask of the calling thread . To ensure that only the caller receives
the signals defined in set, all threads should have signals in set
masked including the calling thread.
If more than one thread is using sigwait() to wait for the same signal,
no more than one of these threads returns from sigwait() with the sig‐
nal number. If more than a single thread is blocked in sigwait() for a
signal when that signal is generated for the process, it is unspecified
which of the waiting threads returns from sigwait(). If the signal is
generated for a specific thread, as by pthread_kill(3C), only that
thread returns.
Should any of the multiple pending signals in the range SIGRTMIN to
SIGRTMAX be selected, it will be the lowest numbered one. The selection
order between realtime and non-realtime signals, or between multiple
pending non-realtime signals, is unspecified.
RETURN VALUES
Upon successful completion, the default version of sigwait() returns a
signal number; the standard-conforming version returns 0 and stores the
received signal number at the location pointed to by sig. Otherwise,
the default version returns -1 and sets errno to indicate an error; the
standard-conforming version returns an error number to indicate the
error.
ERRORS
The sigwait() function will fail if:
EFAULT
The set argument points to an invalid address.
EINTR
The wait was interrupted by an unblocked, caught signal.
EINVAL
The set argument contains an unsupported signal number.
EXAMPLES
Example 1 Creating a thread to handle receipt of a signal
The following sample C code creates a thread to handle the receipt of a
signal. More specifically, it catches the asynchronously generated
signal, SIGINT.
/********************************************************************
*
* compile with -D_POSIX_PTHREAD_SEMANTICS switch;
* required by sigwait()
*
* sigint thread handles delivery of signal. uses sigwait() to wait
* for SIGINT signal.
*
********************************************************************/
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <synch.h>
static void *threadTwo(void *);
static void *threadThree(void *);
static void *sigint(void *);
sigset_t signalSet;
void *
main(void)
{
pthread_t t;
pthread_t t2;
pthread_t t3;
sigfillset ( &signalSet );
/*
* Block signals in initial thread. New threads will
* inherit this signal mask.
*/
pthread_sigmask ( SIG_BLOCK, &signalSet, NULL );
printf("Creating threads\n");
pthread_create(&t, NULL, sigint, NULL);
pthread_create(&t2, NULL, threadTwo, NULL);
pthread_create(&t3, NULL, threadThree, NULL);
printf("##################\n");
printf("press CTRL-C to deliver SIGINT to sigint thread\n");
printf("##################\n");
pthread_exit((void *)0);
}
static void *
threadTwo(void *arg)
{
printf("hello world, from threadTwo [tid: %d]\n",
pthread_self());
printf("threadTwo [tid: %d] is now complete and exiting\n",
pthread_self());
pthread_exit((void *)0);
}
static void *
threadThree(void *arg)
{
printf("hello world, from threadThree [tid: %d]\n",
pthread_self());
printf("threadThree [tid: %d] is now complete and exiting\n",
pthread_self());
pthread_exit((void *)0);
}
void *
sigint(void *arg)
{
int sig;
int err;
printf("thread sigint [tid: %d] awaiting SIGINT\n",
pthread_self());
/*
/* use standard-conforming sigwait()-- 2 args: signal set, signum
*/
err = sigwait ( &signalSet, &sig );
/* test for SIGINT; could catch other signals */
if (err || sig != SIGINT)
abort();
printf("\nSIGINT signal %d caught by sigint thread [tid: %d]\n",
sig, pthread_self());
pthread_exit((void *)0);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Committed │
├────────────────────┼───────────────────┤
│MT-Level │ Async-Signal-Safe │
├────────────────────┼───────────────────┤
│Standard │ See standards(5). │
└────────────────────┴───────────────────┘
SEE ALSOsigaction(2), sigpending(2), sigprocmask(2), sigsuspend(2),
pthread_create(3C), pthread_kill(3C), pthread_sigmask(3C), sig‐
nal.h(3HEAD), attributes(5), standards(5)NOTES
The sigwait() function cannot be used to wait for signals that cannot
be caught (see sigaction(2)). This restriction is silently imposed by
the system.
Solaris 2.4 and earlier releases provided a sigwait() facility as spec‐
ified in POSIX.1c Draft 6. The final POSIX.1c standard changed the
interface as described above. Support for the Draft 6 interface is pro‐
vided for compatibility only and may not be supported in future
releases. New applications and libraries should use the standard-con‐
forming interface.
Apr 16, 2009 SIGWAIT(2)
