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| | sigwait - wait until a signal is posted |
SYNOPSIS
Default
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#include <signal.h> int sigwait(sigset_t *set); |
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POSIX
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cc [ flag ... ] file ... -D_POSIX_PTHREAD_SEMANTICS [ library...]
#include <signal.h> int sigwait(const sigset_t *set, int *sig); |
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The sigwait() function selects a signal in set that is pending on the calling thread (see thr_create(3THR) and pthread_create(3THR).)
If no signal in set is pending, then 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 POSIX version
(see standards(5)) placed in sig. The selection of a signal in set is independent 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 sigwait() is called on an ignored signal, then the occurrence of the signal will be ignored, unless sigaction() changes the disposition. If more than one thread waits for the same signal, only one is unblocked when the signal arrives.
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Upon successful completion, the default version of sigwait() returns a signal number; the POSIX version returns 0 and stores the received signal number at the location pointed to by sig. Otherwise, -1 is returned
and errno is set to indicate an error.
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The sigwait() function will fail if:
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EFAULT
- The set argument points to an invalid address.
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EINTR
- The wait was interrupted by an unblocked, caught signal.
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EINVAL
- The set argument contains an unsupported signal number.
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| | Example 1. Creating a thread to handle receipt of a signal
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The following sample C code creates a thread to handle the receipt of a signal. More specifically, it catches the asynchronously generated signal, SIGINT.
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/********************************************************************
*
* 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 POSIX 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);
}
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See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Async-Signal-Safe |
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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 specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface as described above. Support for the Draft 6 interface is provided for compatibility only and may not be supported in future releases.
New applications and libraries should use the POSIX standard interface.
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