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sigwait(2)
sigwait(2) System Calls sigwait(2)
NAME
sigwait - wait until a signal is posted
SYNOPSIS
#include <signal.h>
int sigwait(const sigset_t *set, int *sig);
POSIX.1c Draft 6
cc [ flag ... ] file ... -D__USE_DRAFT6_PROTOTYPES__ [ library...]
int sigwait(sigset_t *set);
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 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, sigwait() returns 0 and stores the selected
signal number at the location pointed to by sig. Otherwise, sigwait()
returns an error number to indicate the error; it does not set errno.
The Draft 6 version of sigwait() returns the selected signal number on
success. Otherwise, it returns -1 and sets errno 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 sig‐
nal, SIGINT.
/********************************************************************
* 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;
int
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());
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(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
sigaction(2), sigpending(2), sigprocmask(2), sigsuspend(2),
pthread_create(3C), pthread_kill(3C), pthread_sigmask(3C), sig‐
nal.h(3HEAD), attributes(7), standards(7)
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.
Prior to Oracle Solaris 11.4, the default compilation environment pro‐
vided a definition of the sigwait() function as specified in POSIX.1c
Draft 6. The final POSIX.1c standard changed the interface for sig‐
wait(). To allow applications that were written to use the obsolete
Draft-6 interfaces to continue to be compiled and run, the
__USE_DRAFT6_PROTOTYPES__ macro must be defined:
cc -D__USE_DRAFT6_PROTOTYPES__ ...
Support for the Draft-6 interfaces is provided for source compatibility
only and might not be supported in future releases. Old applications
should be converted to use the standard definitions.
Earlier implementations of these interfaces would not wake up on re‐
ceiving a signal with a disposition of SIG_IGN.
Oracle Solaris 11.4 17 Sep 2020 sigwait(2)