SIGNAL(3C) Standard C Library Functions SIGNAL(3C)

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.h(3HEAD) for an explanation of general signal
concepts.


The signal() and sigset() functions 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 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.


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.


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

RETURN VALUES

Upon successful completion, signal() returns the signal's previous
disposition. Otherwise, it returns SIG_ERR and sets errno to indicate
the error.


Upon successful completion, sigset() returns SIG_HOLD if the signal had
been blocked or the signal's previous disposition if it had not been
blocked. Otherwise, it returns SIG_ERR and sets errno to indicate the
error.


Upon successful completion, sighold(), sigrelse(), sigignore(), and
sigpause(), return 0. Otherwise, they return -1 and set errno to
indicate the error.

ERRORS

These functions fail if:

EINTR
A signal was caught during the execution sigpause().


EINVAL
The value of the sig argument is not a valid signal or is equal
to SIGKILL or SIGSTOP.

USAGE

The sighold() function used 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 -1 with errno set to ECHILD (see wait(3C) and
waitid(2)).


The system guarantees that if more than one instance of the same signal
is generated to a process, at least one signal will be received. It does
not guarantee the reception of every generated signal.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

exit(2), kill(2), pause(2), sigaction(2), sigsend(2), waitid(2),
wait(3C), signal.h(3HEAD), attributes(7), standards(7)

September 6, 2007 SIGNAL(3C)