sighold(3)

1SIGSET(3)                  Linux Programmer's Manual                 SIGSET(3)
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NAME

6       sigset, sighold, sigrelse, sigignore - System V signal API
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SYNOPSIS

9       #include <signal.h>
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11       typedef void (*sighandler_t)(int);
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13       sighandler_t sigset(int sig, sighandler_t disp);
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15       int sighold(int sig);
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17       int sigrelse(int sig);
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19       int sigignore(int sig);
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21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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23       sigset(), sighold(), sigrelse(), sigignore():
24           _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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DESCRIPTION

27       These  functions are provided in glibc as a compatibility interface for
28       programs that make use of the historical System V signal API.  This API
29       is  obsolete:  new applications should use the POSIX signal API (sigac‐
30       tion(2), sigprocmask(2), etc.)
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32       The sigset() function modifies the disposition of the signal sig.   The
33       disp  argument  can be the address of a signal handler function, or one
34       of the following constants:
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36       SIG_DFL
37              Reset the disposition of sig to the default.
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39       SIG_IGN
40              Ignore sig.
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42       SIG_HOLD
43              Add sig to the process's signal mask, but leave the  disposition
44              of sig unchanged.
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46       If disp specifies the address of a signal handler, then sig is added to
47       the process's signal mask during execution of the handler.
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49       If disp was specified as a value  other  than  SIG_HOLD,  then  sig  is
50       removed from the process's signal mask.
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52       The dispositions for SIGKILL and SIGSTOP cannot be changed.
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54       The sighold() function adds sig to the calling process's signal mask.
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56       The  sigrelse()  function removes sig from the calling process's signal
57       mask.
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59       The sigignore() function sets the disposition of sig to SIG_IGN.
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RETURN VALUE

62       On success, sigset() returns SIG_HOLD if sig  was  blocked  before  the
63       call, or the signal's previous disposition if it was not blocked before
64       the call.  On error, sigset() returns -1, with errno  set  to  indicate
65       the error.  (But see BUGS below.)
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67       The  sighold(),  sigrelse(), and sigignore() functions return 0 on suc‐
68       cess; on error, these functions return -1 and set errno to indicate the
69       error.
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ERRORS

72       For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).
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74       For sighold() and sigrelse() see the ERRORS under sigprocmask(2).
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76       For sigignore(), see the errors under sigaction(2).
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CONFORMING TO

79       SVr4,  POSIX.1-2001.   These functions are obsolete: do not use them in
80       new programs.  POSIX.1-2008 marks sighold(),  sigignore(),  sigpause(),
81       sigrelse(),  and  sigset()  as obsolete, recommending the use of sigac‐
82       tion(2), sigprocmask(2), pthread_sigmask(3), and sigsuspend(2) instead.
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NOTES

85       These functions appeared in glibc version 2.1.
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87       The sighandler_t type is a GNU extension; it is used on this page  only
88       to make the sigset() prototype more easily readable.
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90       The  sigset()  function provides reliable signal handling semantics (as
91       when calling sigaction(2) with sa_mask equal to 0).
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93       On System V, the signal() function provides  unreliable  semantics  (as
94       when calling sigaction(2) with sa_mask equal to SA_RESETHAND | SA_NODE‐
95       FER).  On BSD,  signal()  provides  reliable  semantics.   POSIX.1-2001
96       leaves  these  aspects of signal() unspecified.  See signal(2) for fur‐
97       ther details.
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99       In order to wait for a signal, BSD and System V both provided  a  func‐
100       tion  named  sigpause(3), but this function has a different argument on
101       the two systems.  See sigpause(3) for details.
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BUGS

104       In versions of glibc before 2.2, sigset() did not unblock sig  if  disp
105       was specified as a value other than SIG_HOLD.
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107       In versions of glibc before 2.5, sigset() does not correctly return the
108       previous disposition of the signal in two cases.   First,  if  disp  is
109       specified  as  SIG_HOLD,  then  a  successful  sigset()  always returns
110       SIG_HOLD.  Instead, it should return the previous  disposition  of  the
111       signal (unless the signal was blocked, in which case SIG_HOLD should be
112       returned).  Second, if the signal is currently blocked, then the return
113       value of a successful sigset() should be SIG_HOLD.  Instead, the previ‐
114       ous disposition of the signal is returned.  These  problems  have  been
115       fixed since glibc 2.5.
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COLOPHON

122       This page is part of release 3.53 of the Linux  man-pages  project.   A
123       description  of  the project, and information about reporting bugs, can
124       be found at http://www.kernel.org/doc/man-pages/.
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128Linux                             2010-09-20                         SIGSET(3)