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PTHREAD_SIGMASK(3P) POSIX Programmer's Manual PTHREAD_SIGMASK(3P)
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.
pthread_sigmask, sigprocmask — examine and change blocked signals
#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);
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
signals 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 signal 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
sigprocmask(), 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.
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.
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.
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;
}
}
None.
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 signal(), it is unspecified whether this occurs.
See kill() for a discussion of the requirement on delivery of
signals.
None.
exec(1p), kill(3p), sigaction(3p), sigaddset(3p), sigdelset(3p),
sigemptyset(3p), sigfillset(3p), sigismember(3p), sigpending(3p),
sigqueue(3p), sigsuspend(3p)
The Base Definitions volume of POSIX.1‐2008, signal.h(0p)
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PTHREAD_SIGMASK(3P)
Pages that refer to this page: signal.h(0p), exec(3p), sigaction(3p), sigaddset(3p), sigdelset(3p), sigemptyset(3p), sigfillset(3p), sighold(3p), sigismember(3p), siglongjmp(3p), sigpending(3p), sigprocmask(3p), sigsetjmp(3p), sigtimedwait(3p), sigwait(3p)