PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

SIGWAIT(3P)               POSIX Programmer's Manual              SIGWAIT(3P)

PROLOG         top

       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         top

       sigwait — wait for queued signals

SYNOPSIS         top

       #include <signal.h>

       int sigwait(const sigset_t *restrict set, int *restrict sig);

DESCRIPTION         top

       The sigwait() function shall select a pending signal from set,
       atomically clear it from the system's set of pending signals, and
       return that signal number in the location referenced by sig.  If
       prior to the call to sigwait() there are multiple pending instances
       of a single signal number, it is implementation-defined whether upon
       successful return there are any remaining pending signals for that
       signal number.  If the implementation supports queued signals and
       there are multiple signals queued for the signal number selected, the
       first such queued signal shall cause a return from sigwait() and the
       remainder shall remain queued. If no signal in set is pending at the
       time of the call, the thread shall be suspended until one or more
       becomes pending. The signals defined by set shall have been blocked
       at the time of the call to sigwait(); otherwise, the behavior is
       undefined. The effect of sigwait() on the signal actions for the
       signals in set is unspecified.

       If more than one thread is using sigwait() to wait for the same
       signal, no more than one of these threads shall return from sigwait()
       with the signal number. If more than a single thread is blocked in
       sigwait() for a signal when that signal is generated for the process,
       it is unspecified which of the waiting threads returns from
       sigwait().  If the signal is generated for a specific thread, as by
       pthread_kill(), only that thread shall return.

       Should any of the multiple pending signals in the range SIGRTMIN to
       SIGRTMAX be selected, it shall be the lowest numbered one. The
       selection order between realtime and non-realtime signals, or between
       multiple pending non-realtime signals, is unspecified.

RETURN VALUE         top

       Upon successful completion, sigwait() shall store the signal number
       of the received signal at the location referenced by sig and return
       zero. Otherwise, an error number shall be returned to indicate the
       error.

ERRORS         top

       The sigwait() function may fail if:

       EINVAL The set argument contains an invalid or unsupported signal
              number.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       To provide a convenient way for a thread to wait for a signal, this
       volume of POSIX.1‐2008 provides the sigwait() function. For most
       cases where a thread has to wait for a signal, the sigwait() function
       should be quite convenient, efficient, and adequate.

       However, requests were made for a lower-level primitive than
       sigwait() and for semaphores that could be used by threads. After
       some consideration, threads were allowed to use semaphores and
       sem_post() was defined to be async-signal-safe.

       In summary, when it is necessary for code run in response to an
       asynchronous signal to notify a thread, sigwait() should be used to
       handle the signal. Alternatively, if the implementation provides
       semaphores, they also can be used, either following sigwait() or from
       within a signal handling routine previously registered with
       sigaction().

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.4, Signal Concepts, Section 2.8.1, Realtime Signals,
       pause(3p), pthread_sigmask(3p), sigaction(3p), sigpending(3p),
       sigsuspend(3p), sigtimedwait(3p)

       The Base Definitions volume of POSIX.1‐2008, signal.h(0p), time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                         SIGWAIT(3P)

Pages that refer to this page: signal.h(0p)sigtimedwait(3p)