# sigsuspend

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           sigsuspend — wait for a signal
    


## SYNOPSIS



           #include <signal.h>
    
           int sigsuspend(const sigset_t *_sigmask_);
    


## DESCRIPTION



           The _sigsuspend_() function shall replace the current signal mask of
           the calling thread with the set of signals pointed to by _sigmask_
           and then suspend the thread until delivery of a signal whose
           action is either to execute a signal-catching function or to
           terminate the process. This shall not cause any other signals that
           may have been pending on the process to become pending on the
           thread.
    
           If the action is to terminate the process then _sigsuspend_() shall
           never return. If the action is to execute a signal-catching
           function, then _sigsuspend_() shall return after the signal-catching
           function returns, with the signal mask restored to the set that
           existed prior to the _sigsuspend_() call.
    
           It is not possible to block signals that cannot be ignored. This
           is enforced by the system without causing an error to be
           indicated.
    


## RETURN VALUE



           Since _sigsuspend_() suspends thread execution indefinitely, there
           is no successful completion return value. If a return occurs, -1
           shall be returned and _errno_ set to indicate the error.
    


## ERRORS



           The _sigsuspend_() function shall fail if:
    
           **EINTR** A signal is caught by the calling process and control is
                  returned from the signal-catching function.
    
           _The following sections are informative._
    


## EXAMPLES



           None.
    


## APPLICATION USAGE



           Normally, at the beginning of a critical code section, a specified
           set of signals is blocked using the _sigprocmask_() function. When
           the thread has completed the critical section and needs to wait
           for the previously blocked signal(s), it pauses by calling
           _sigsuspend_() with the mask that was returned by the _sigprocmask_()
           call.
    


## RATIONALE



           Code which wants to avoid the ambiguity of the signal mask for
           thread cancellation handlers can install an additional
           cancellation handler which resets the signal mask to the expected
           value.
    
               void cleanup(void *arg)
               {
                   sigset_t *ss = (sigset_t *) arg;
                   pthread_sigmask(SIG_SETMASK, ss, NULL);
               }
    
               int call_sigsuspend(const sigset_t *mask)
               {
                   sigset_t oldmask;
                   int result;
                   pthread_sigmask(SIG_SETMASK, NULL, &oldmask);
                   pthread_cleanup_push(cleanup, &oldmask);
                   result = sigsuspend(sigmask);
                   pthread_cleanup_pop(0);
                   return result;
               }
    


## FUTURE DIRECTIONS



           None.
    


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