sigpause(3C)

NAME

sigpause — atomically release blocked signals and wait for interrupt

SYNOPSIS

#include <signal.h>

long sigpause(long mask);

DESCRIPTION

sigpause() blocks signals according to the value of mask in the same manner as sigsetmask(2), then atomically waits for an unmasked signal to arrive. On return, sigpause() restores the current signal mask to the value that existed before the sigpause() call. When no signals are to be blocked, a value of 0L is used for mask.

In normal usage, a signal is blocked using sigblock() (see sigblock(2)). To begin a critical section, variables modified on the occurrence of the signal are examined to determine that there is no work to be done, and the process pauses, awaiting work by using sigpause() with the mask returned by sigblock().

RETURN VALUE

sigpause() terminates when it is interrupted by a signal. When sigpause() terminates, it returns -l and sets errno to EINTR.

EXAMPLES

The following call to sigpause() waits until the calling process receives a signal:

sigpause (0L); 

The following example blocks the SIGIO signal until sigpause() is called. When a signal is received at the sigpause() statement, the signal mask is restored to its value before sigpause() was called:

long savemask; 
savemask = sigblock (sigmask (SIGIO)); 
/* critical section */ 
sigpause (savemask); 

WARNINGS

Check all references to signal(5) for appropriateness on systems that support sigvector(2). sigvector() can affect the behavior described on this page.

Do not use sigpause() in conjunction with the facilities described under sigset(3C).

APPLICATION USAGE

Threads Considerations

Since blocked signal masks are maintained at the thread level, sigpause() modifies only the calling thread's blocked signal mask. sigpause() suspends only the calling thread until it receives a signal.

If other threads in the process do not block the signal, the signal may be delivered to another thread in the process and the thread in sigpause() may continue waiting. For this reason, the use of sigwait(2) is recommended instead of sigpause() for multi-threaded applications.

For more information regarding signals and threads, refer to signal(5).

LP64 Programs

sigpause() accepts a long (64 bit) value. However, as for ILP32 programs, sigpause() supports signals numbered 1 through 32. The upper 32 bits of the mask argument are ignored.

AUTHOR

sigpause() was developed by the University of California, Berkeley.