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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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
       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.

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 aa 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
       signal(), 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.1-2017, <signal.h>

COPYRIGHT
       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 http://www.opengroup.org/unix/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                  2017                   PTHREAD_SIGMASK(3)
