SIGSET(3)



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

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

SYNOPSIS
       #define _XOPEN_SOURCE 500
       #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);

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       is  obsolete:  new applications should use the POSIX signal API (sigac-
       tion(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 signal 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.

       The  sighold(),  sigrelse(), and sigignore() functions return 0 on suc-
       cess; 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).

NOTES
       These functions appeared in glibc version 2.1.

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

       The sigset() function provides reliable signal handling  semantics  (as
       when calling sigaction() with sa_mask equal to 0).

       On  System  V,  the signal() function provides unreliable semantics (as
       when calling sigaction() with sa_mask equal to SA_RESETHAND |  SA_NODE-
       FER).   On  BSD,  signal()  provides  reliable semantics.  POSIX.1-2001
       leaves these aspects of signal() unspecified.  See signal(2)  for  fur-
       ther details.

       In  order  to wait for a signal, BSD and System V both provided a func-
       tion named sigpause(), 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 all versions of glibc up to and including 2.3.5, sigset()  does  not
       correctly  return  the previous disposition of the signal in two cases.
       First, if disp is specified as SIG_HOLD,  then  a  successful  sigset()
       always returns SIG_HOLD.  Instead, it should return the previous dispo-
       sition 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.

CONFORMING TO
       SVr4, POSIX.1-2001.  These functions are obsolete: do not use  them  in
       new programs.

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

Linux 2.6.14                      2005-12-01                         SIGSET(3)

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