pthread_sigmask(3p) — Linux manual page


PTHREAD_SIGMASK(3P)       POSIX Programmer's Manual      PTHREAD_SIGMASK(3P)

PROLOG         top

       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         top

       pthread_sigmask, sigprocmask — examine and change blocked signals

SYNOPSIS         top

       #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         top

       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

       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

       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

       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

       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

       The use of the sigprocmask() function is unspecified in a multi-
       threaded process.

RETURN VALUE         top

       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         top

       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

       The following sections are informative.

EXAMPLES         top

   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);



RATIONALE         top

       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



SEE ALSO         top

       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)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                 PTHREAD_SIGMASK(3P)

Pages that refer to this page: signal.h(0p)exec(3p)execl(3p)execle(3p)execlp(3p)execv(3p)execve(3p)execvp(3p)sigaction(3p)sigaddset(3p)sigdelset(3p)sigemptyset(3p)sigfillset(3p)sighold(3p)sigignore(3p)sigismember(3p)siglongjmp(3p)sigpending(3p)sigprocmask(3p)sigset(3p)sigsetjmp(3p)sigtimedwait(3p)sigwait(3p)