SIGSET(3)                           Linux Programmer's Manual                           SIGSET(3)



NAME
       sigset, sighold, sigrelse, sigignore - System V signal API

SYNOPSIS
       #include <signal.h>

       typedef void (*sighandler_t)(int);

       sighandler_t sigset(int sig, sighandler_t disp);

       int sighold(int sig);

       int sigrelse(int sig);

       int sigignore(int sig);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigset(), sighold(), sigrelse(), sigignore():
           _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       These  functions are provided in glibc as a compatibility interface for programs that make
       use of the historical System V signal API.  This API is obsolete: new applications  should
       use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)

       The  sigset()  function modifies the disposition of the signal sig.  The disp argument can
       be the address of a signal handler function, or one of the following constants:

       SIG_DFL
              Reset the disposition of sig to the default.

       SIG_IGN
              Ignore sig.

       SIG_HOLD
              Add sig to the process's signal mask, but leave the disposition of sig unchanged.

       If disp specifies the address of a signal handler, then sig is added to the process's sig‐
       nal mask during execution of the handler.

       If  disp  was  specified  as  a  value  other  than SIG_HOLD, then sig is removed from the
       process's signal mask.

       The dispositions for SIGKILL and SIGSTOP cannot be changed.

       The sighold() function adds sig to the calling process's signal mask.

       The sigrelse() function removes sig from the calling process's signal mask.

       The sigignore() function sets the disposition of sig to SIG_IGN.

RETURN VALUE
       On success, sigset() returns SIG_HOLD if sig was blocked before the call, or the  signal's
       previous  disposition  if  it was not blocked before the call.  On error, sigset() returns
       -1, with errno set to indicate the error.  (But see BUGS below.)

       The sighold(), sigrelse(), and sigignore() functions return 0 on success; on error,  these
       functions return -1 and set errno to indicate the error.

ERRORS
       For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).

       For sighold() and sigrelse() see the ERRORS under sigprocmask(2).

       For sigignore(), see the errors under sigaction(2).

CONFORMING TO
       SVr4,  POSIX.1-2001.   These  functions  are  obsolete:  do  not use them in new programs.
       POSIX.1-2008 marks sighold(), sigignore(), sigpause(), sigrelse(), and sigset()  as  obso‐
       lete,  recommending  the use of sigaction(2), sigprocmask(2), pthread_sigmask(3), and sig‐
       suspend(2) instead.

NOTES
       These functions appeared in glibc version 2.1.

       The sighandler_t type is a GNU extension; it is  used  on  this  page  only  to  make  the
       sigset() prototype more easily readable.

       The  sigset() function provides reliable signal handling semantics (as when calling sigac‐
       tion(2) with sa_mask equal to 0).

       On System V, the signal() function provides unreliable semantics (as when  calling  sigac‐
       tion(2) with sa_mask equal to SA_RESETHAND | SA_NODEFER).  On BSD, signal() provides reli‐
       able semantics.  POSIX.1-2001 leaves these aspects of signal() unspecified.  See signal(2)
       for further details.

       In  order  to  wait  for  a  signal,  BSD and System V both provided a function named sig‐
       pause(3), but this function has a different argument on the two systems.  See  sigpause(3)
       for details.

BUGS
       In  versions  of glibc before 2.2, sigset() did not unblock sig if disp was specified as a
       value other than SIG_HOLD.

       In versions of glibc before 2.5, sigset() does not correctly return the previous  disposi‐
       tion of the signal in two cases.  First, if disp is specified as SIG_HOLD, then a success‐
       ful sigset() always returns SIG_HOLD.  Instead, it should return the previous  disposition
       of  the signal (unless the signal was blocked, in which case SIG_HOLD should be returned).
       Second, if the signal is currently blocked, then the return value of a successful sigset()
       should  be  SIG_HOLD.  Instead, the previous disposition of the signal is returned.  These
       problems have been fixed since glibc 2.5.

SEE ALSO
       kill(2),  pause(2),  sigaction(2),  signal(2),  sigprocmask(2),   raise(3),   sigpause(3),
       sigvec(3), signal(7)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2010-09-20                                  SIGSET(3)