sigwait(3p) — Linux manual page


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

       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

       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

       The following sections are informative.

EXAMPLES         top




RATIONALE         top

       To provide a convenient way for a thread to wait for a signal,
       this volume of POSIX.1‐2017 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().



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.1‐2017, signal.h(0p),

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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 .

       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 .

IEEE/The Open Group               2017                       SIGWAIT(3P)

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