NAME

sighold, sigignore, sigpause, sigrelse, sigset - signal management

SYNOPSIS

[XSI] #include <signal.h>

int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);

DESCRIPTION

Use of any of these functions is unspecified in a multi-threaded process.

The sighold(), sigignore(), sigpause(), sigrelse(), and sigset() functions provide simplified signal management.

The sigset() function shall modify signal dispositions. The sig argument specifies the signal, which may be any signal except SIGKILL and SIGSTOP. The disp argument specifies the signal's disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal handler. If sigset() is used, and disp is the address of a signal handler, the system shall add sig to the calling process' signal mask before executing the signal handler; when the signal handler returns, the system shall restore the calling process' signal mask to its state prior to the delivery of the signal. In addition, if sigset() is used, and disp is equal to SIG_HOLD, sig shall be added to the calling process' signal mask and sig's disposition shall remain unchanged. If sigset() is used, and disp is not equal to SIG_HOLD, sig shall be removed from the calling process' signal mask.

The sighold() function shall add sig to the calling process' signal mask.

The sigrelse() function shall remove sig from the calling process' signal mask.

The sigignore() function shall set the disposition of sig to SIG_IGN.

The sigpause() function shall remove sig from the calling process' signal mask and suspend the calling process until a signal is received. The sigpause() function shall restore the process' signal mask to its original state before returning.

If the action for the SIGCHLD signal is set to SIG_IGN, child processes of the calling processes shall not be transformed into zombie processes when they terminate. If the calling process subsequently waits for its children, and the process has no unwaited-for children that were transformed into zombie processes, it shall block until all of its children terminate, and wait(), waitid(), and waitpid() shall fail and set errno to [ECHILD].

RETURN VALUE

Upon successful completion, sigset() shall return SIG_HOLD if the signal had been blocked and the signal's previous disposition if it had not been blocked. Otherwise, SIG_ERR shall be returned and errno set to indicate the error.

The sigpause() function shall suspend execution of the thread until a signal is received, whereupon it shall return -1 and set errno to [EINTR].

For all other functions, upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to indicate the error.

ERRORS

These functions shall fail if:

[EINVAL]

The sig argument is an illegal signal number.

The sigset() and sigignore() functions shall fail if:

[EINVAL]

An attempt is made to catch a signal that cannot be caught, or to ignore a signal that cannot be ignored.

EXAMPLES

None.

APPLICATION USAGE

The sigaction() function provides a more comprehensive and reliable mechanism for controlling signals; new applications should use sigaction() rather than sigset().

The sighold() function, in conjunction with sigrelse() or sigpause(), may be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

The sigsuspend() function should be used in preference to sigpause() for broader portability.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

Signal Concepts, exec(), pause(), sigaction(), signal(), sigsuspend(), waitid(), the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

The DESCRIPTION is updated to indicate that the sigpause() function restores the process' signal mask to its original state before returning.

The RETURN VALUE section is updated to indicate that the sigpause() function suspends execution of the process until a signal is received, whereupon it returns -1 and sets errno to [EINTR].

Issue 6

The DESCRIPTION is updated to avoid use of the term "must" for application requirements.

References to the wait3() function are removed.

The XSI functions are split out into their own reference page.