NAME

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

SYNOPSIS

#include <signal.h>

void (∗sigset (sig, func))()
int sig;
void (∗func)();

int sighold (sig)
int sig;

int sigrelse (sig)
int sig;

int sigignore (sig)
int sig;

int sigpause (sig)
int sig;

DESCRIPTION

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

sigset specifies the system signal action to be taken upon receipt of a signal.  sig specifies the signal, which may be any signal except SIGKILL and SIGSTOP.  func specifies the signal’s disposition, which may be SIG_DFL, SIG_IGN, SIG_HOLD, or the address of a signal handler. 

If func is SIG_DFL, the default action for signal sig is reinstated; this default is usually termination [see signal(5)].  If func is SIG_IGN the signal is subsequently ignored and pending instances of the signal are discarded.  If func is SIG_HOLD the signal is held upon receipt (and its previous disposition is otherwise unaffected).  Any pending signal of this type remains held.  Only one signal of each type is held.  Otherwise, when the signal occurs further occurences of the signal are automatically blocked and func is called. 

For information on the signal handler interface, see signal(5). 

When a signal handler function is specified for a signal being delivered, 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.  If a non-local goto (longjmp) is taken, then sigrelse must be called to restore the system signal action and release any held signal of this type. 

In general, upon return from the signal-catching handler, the receiving process will resume execution at the point it was interrupted.  However, when a signal is caught during a read(2), a write(2), an open(2), or an ioctl(2) system call on a slow device, during a pause(2) system call, or during a wait(2) system call that does not return immediately due to the existence of a previously stopped or zombie process, the signal-catching handler will be executed and then the interrupted system call may return a −1 to the calling process with errno set to EINTR. 

Unlike the signal(2) facilities, the handler func remains installed after a signal has been delivered. 

sighold and sigrelse are used to establish critical regions of code.  sighold adds sig to the calling process’s signal mask; it is analogous to raising the priority level and deferring or holding a signal until the priority is lowered by sigrelse.  sigrelse removes sig from the calling process’s signal mask, restoring the system signal action to that specified previously by sigset. 

sigignore sets the action for signal sig to SIG_IGN (see above). 

sigpause suspends the calling process until it receives a signal, the same as pause(2).  However, if the signal sig had been received and held, it is released (removed from the current signal mask) and the system signal action taken.  This system call is useful for testing variables that are changed on the occurrence of a signal.  The correct usage is to use sighold to block the signal first, then test the variables.  If they have not changed, then call sigpause to wait for the signal.  When the sigpause returns, the original signal mask is restored. 

RETURN VALUE

Upon successful completion, sigset returns the previous value of the system signal action for the specified signal sig, or SIG_HOLD if it had been blocked.  Otherwise, a value of SIG_ERR is returned and errno is set to indicate the error.  SIG_ERR is defined in <signal.h>.

For the other functions, upon successful completion, a value of 0 is returned.  Otherwise, a value of −1 is returned and errno is set to indicate the error. 

ERRORS

These functions will fail if one or more of the following are true:

­[EINVAL] sig is an illegal signal number (including SIGKILL and SIGSTOP) or the default handling of sig cannot be changed. 

­[EINTR] A signal was caught during the system call sigpause. 

SEE ALSO

kill(2), pause(2), sigaction(2), signal(2), wait(2), setjmp(3C), signal(5). 

NOTES

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

If the disposition of SIGCHLD is set 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), sigaction(2), signal(5)]. 

The other signal management functions, signal(2) and pause(2), should not be used in conjunction with these routines for a particular signal type. 

CX/UX Programmer’s Reference Manual