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Name

signal, sigset, sighold, sigrelse, sigignore, sigpause - simplified signal management for application processes

Synopsis

#include <signal.h>

void (*signal (int sig, void (*disp)(int)))(int);

void (*sigset (int sig, void (*disp)(int)))(int);

int sighold(int sig);

int sigrelse(int sig);

int sigignore(int sig);

int sigpause(int sig);

Description

These functions provide simplified signal management for application processes. See signal(5) for an explanation of general signal concepts.

signal() and sigset() are used to modify signal dispositions. sig specifies the signal, which may be any signal except SIGKILL and SIGSTOP. disp specifies the signal’s disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal handler. If signal() is used, disp is the address of a signal handler, and sig is not SIGILL, SIGTRAP, or SIGPWR, the system first sets the signal’s disposition to SIG_DFL before executing the signal handler. If sigset() is used and disp is the address of a signal handler, the system adds sig to the calling process’s signal mask before executing the signal handler; when the signal handler returns, the system restores the calling process’s 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 is added to the calling process’s signal mask and the signal’s disposition remains unchanged.

sighold() adds sig to the calling process’s signal mask.

sigrelse() removes sig from the calling process’s signal mask.

sigignore() sets the disposition of sig to SIG_IGN.

sigpause() removes sig from the calling process’s signal mask and suspends the calling process until a signal is received.

Return Values

On success, signal() returns the signal’s previous disposition. On failure, it returns SIG_ERR and sets errno to indicate the error.

On success, sigset() returns SIG_HOLD if the signal had been blocked or the signal’s previous disposition if it had not been blocked. On failure, it returns SIG_ERR and sets errno to indicate the error.

All other functions return zero on success. On failure, they return -1 and set errno to indicate the error.

Errors

These functions fail if any of the following are true:

EINTR
A signal was caught during the function sigpause().
EINVAL
The value of the sig argument is not a valid signal or is equal to SIGKILL or SIGSTOP.

See Also

kill(2) , pause(2) , sigaction(2) , sigsend(2) , wait(2) , waitid(2) , signal(5)

Notes

sighold() 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.

If signal() or sigset() is used to set SIGCHLD’s disposition to a signal handler, SIGCHLD will not be sent when the calling process’s children are stopped or continued.

If any of the above functions are used to set SIGCHLD’s disposition to SIG_IGN, the calling process’s child processes will not create zombie processes when they terminate (see exit(2) ). If the calling process subsequently waits for its children, it blocks until all of its children terminate; it then returns a value of -1 with errno set to ECHILD (see wait(2) , waitid(2) ).

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