PTHREAD_SIGMASK(3P) POSIX Programmer's Manual PTHREAD_SIGMASK(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
pthread_sigmask, sigprocmask — examine and change blocked signals
SYNOPSIS
#include <signal.h>
int pthread_sigmask(int how, const sigset_t *restrict set,
sigset_t *restrict oset);
int sigprocmask(int how, const sigset_t *restrict set,
sigset_t *restrict oset);
DESCRIPTION
The pthread_sigmask() function shall examine or change (or both) the
calling thread's signal mask, regardless of the number of threads in
the process. The function shall be equivalent to sigprocmask(), without
the restriction that the call be made in a single-threaded process.
In a single-threaded process, the sigprocmask() function shall examine
or change (or both) the signal mask of the calling thread.
If the argument set is not a null pointer, it points to a set of sig‐
nals to be used to change the currently blocked set.
The argument how indicates the way in which the set is changed, and the
application shall ensure it consists of one of the following values:
SIG_BLOCK The resulting set shall be the union of the current set and
the signal set pointed to by set.
SIG_SETMASK The resulting set shall be the signal set pointed to by
set.
SIG_UNBLOCK The resulting set shall be the intersection of the current
set and the complement of the signal set pointed to by set.
If the argument oset is not a null pointer, the previous mask shall be
stored in the location pointed to by oset. If set is a null pointer,
the value of the argument how is not significant and the thread's sig‐
nal mask shall be unchanged; thus the call can be used to enquire about
currently blocked signals.
If there are any pending unblocked signals after the call to sigproc‐
mask(), at least one of those signals shall be delivered before the
call to sigprocmask() returns.
It is not possible to block those signals which cannot be ignored.
This shall be enforced by the system without causing an error to be
indicated.
If any of the SIGFPE, SIGILL, SIGSEGV, or SIGBUS signals are generated
while they are blocked, the result is undefined, unless the signal was
generated by the action of another process, or by one of the functions
kill(), pthread_kill(), raise(), or sigqueue().
If sigprocmask() fails, the thread's signal mask shall not be changed.
The use of the sigprocmask() function is unspecified in a multi-
threaded process.
RETURN VALUE
Upon successful completion pthread_sigmask() shall return 0; otherwise,
it shall return the corresponding error number.
Upon successful completion, sigprocmask() shall return 0; otherwise, −1
shall be returned, errno shall be set to indicate the error, and the
signal mask of the process shall be unchanged.
ERRORS
The pthread_sigmask() and sigprocmask() functions shall fail if:
EINVAL The value of the how argument is not equal to one of the defined
values.
The pthread_sigmask() function shall not return an error code of
[EINTR].
The following sections are informative.
EXAMPLES
Signaling in a Multi-Threaded Process
This example shows the use of pthread_sigmask() in order to deal with
signals in a multi-threaded process. It provides a fairly general
framework that could be easily adapted/extended.
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
...
static sigset_t signal_mask; /* signals to block */
int main (int argc, char *argv[])
{
pthread_t sig_thr_id; /* signal handler thread ID */
int rc; /* return code */
sigemptyset (&signal_mask);
sigaddset (&signal_mask, SIGINT);
sigaddset (&signal_mask, SIGTERM);
rc = pthread_sigmask (SIG_BLOCK, &signal_mask, NULL);
if (rc != 0) {
/* handle error */
...
}
/* any newly created threads inherit the signal mask */
rc = pthread_create (&sig_thr_id, NULL, signal_thread, NULL);
if (rc != 0) {
/* handle error */
...
}
/* APPLICATION CODE */
...
}
void *signal_thread (void *arg)
{
int sig_caught; /* signal caught */
int rc; /* returned code */
rc = sigwait (&signal_mask, &sig_caught);
if (rc != 0) {
/* handle error */
}
switch (sig_caught)
{
case SIGINT: /* process SIGINT */
...
break;
case SIGTERM: /* process SIGTERM */
...
break;
default: /* should normally not happen */
fprintf (stderr, "\nUnexpected signal %d\n", sig_caught);
break;
}
}
APPLICATION USAGE
None.
RATIONALE
When a thread's signal mask is changed in a signal-catching function
that is installed by sigaction(), the restoration of the signal mask on
return from the signal-catching function overrides that change (see
sigaction()). If the signal-catching function was installed with sig‐
nal(), it is unspecified whether this occurs.
See kill() for a discussion of the requirement on delivery of signals.
FUTURE DIRECTIONS
None.
SEE ALSO
exec, kill(), sigaction(), sigaddset(), sigdelset(), sigemptyset(),
sigfillset(), sigismember(), sigpending(), sigqueue(), sigsuspend()
The Base Definitions volume of POSIX.1‐2008, <signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PTHREAD_SIGMASK(3P)
