sigrelse(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

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   is   obsolete:  new  applications  should  use  the  POSIX  signal  API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 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.  (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).

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   ┌────────────────────────┬───────────────┬─────────┐
   │Interface               │ Attribute     │ Value   │
   ├────────────────────────┼───────────────┼─────────┤
   │sigset(), sighold(),    │ Thread safety │ MT-Safe │
   │sigrelse(), sigignore() │               │         │
   └────────────────────────┴───────────────┴─────────┘

CONFORMING TO

   SVr4, POSIX.1-2001, POSIX.1-2008.  These functions are obsolete: do not
   use  them  in new programs.  POSIX.1-2008 marks sighold(), sigignore(),
   sigpause(3), sigrelse(), and sigset() as obsolete, recommending the use
   of  sigaction(2), sigprocmask(2), pthread_sigmask(3), and sigsuspend(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 sigaction(2) with sa_mask equal to 0).

   On System V, the signal() function provides  unreliable  semantics  (as
   when   calling  sigaction(2)  with  sa_mask  equal  to  SA_RESETHAND  |
   SA_NODEFER).    On   BSD,   signal()   provides   reliable   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 sigpause(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 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  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 4.09 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
   https://www.kernel.org/doc/man-pages/.

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