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)):
sigset(),
sighold(),
sigrelse(),
sigignore():
_XOPEN_SOURCE >= 500
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 This API is obsolete: new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.
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
sigignore(), see the errors under
sigaction(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.
kill(2),
pause(2),
sigaction(2),
signal(2),
sigprocmask(2),
raise(3),
sigpause(3),
sigvec(3),
signal(7)