sigset(3) Library Functions Manual sigset(3)
NAME
sigset, sighold, sigrelse, sigignore - System V signal API
LIBRARY
Standard C library (libc, -lc)
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is obsolete: new applications should use the POSIX signal API (sigac-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 re-
moved 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 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).
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│sigset(), sighold(), sigrelse(), │ Thread safety │ MT-Safe │
│sigignore() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
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 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_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(3), but this function has a different argument on
the two systems. See sigpause(3) for details.
BUGS
Before glibc 2.2, sigset() did not unblock sig if disp was specified as
a value other than SIG_HOLD.
Before glibc 2.5, sigset() does not correctly return the previous dis-
position 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). Sec-
ond, if the signal is currently blocked, then the return value of a
successful sigset() should be SIG_HOLD. Instead, the previous disposi-
tion 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)
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