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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 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 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 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.1‐2008, <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 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 .