sigset(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       #define _XOPEN_SOURCE 500
10       #include <signal.h>
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12       typedef void (*sighandler_t)(int);
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14       sighandler_t sigset(int sig, sighandler_t disp);
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16       int sighold(int sig);
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18       int sigrelse(int sig);
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20       int sigignore(int sig);
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DESCRIPTION

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25       is  obsolete:  new applications should use the POSIX signal API (sigac‐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

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

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

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

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

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

118       This page is part of release 3.25 of the Linux  man-pages  project.   A
119       description  of  the project, and information about reporting bugs, can
120       be found at http://www.kernel.org/doc/man-pages/.
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124Linux                             2009-03-15                         SIGSET(3)