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

       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

       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  */
               case SIGTERM:    /* process SIGTERM */
               default:         /* should normally not happen */
                   fprintf (stderr, "\nUnexpected signal %d\n", sig_caught);


       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.


       exec, kill(), sigaction(), sigaddset(), sigdelset(), sigemptyset(),
       sigfillset(), sigismember(), sigpending(), sigqueue(), sigsuspend()

       The Base Definitions volume of POSIX.1‐2017, <signal.h>

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute
       of Electrical and Electronics Engineers, Inc and The Open Group.  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 .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
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IEEE/The Open Group                   2017                   PTHREAD_SIGMASK(3P)