sigset, sighold, sigrelse, sigignore - System V signal API
typedef void (*sighandler_t)(int);
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 This API is obsolete: new applications should use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)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
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.
sig to the process's signal mask, but leave the disposition of
disp specifies the address of a signal handler, then
sig is added to the process's signal mask during execution of the handler.
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.)
These functions appeared in glibc version 2.1.
sighandler_t type is a GNU extension; it is used on this page only to make the sigset() prototype more easily readable.
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 versions of glibc before 2.2, sigset() did not unblock
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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