sigset, sighold, sigrelse, sigignore - System V signal API
#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)):
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 This API is obsolete: new applications should use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)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:
Reset the disposition of sig to the default.
Ignore sig.
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.
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.
For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).
For sighold() and sigrelse() see the ERRORS under sigprocmask(2).
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| sigset(),
sighold(), sigrelse(), sigignore() |
Thread safety | MT-Safe |
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.
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.
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.
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