1SIGWAIT(3P) POSIX Programmer's Manual SIGWAIT(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 sigwait — wait for queued signals
13
15 #include <signal.h>
16 int sigwait(const sigset_t *restrict set, int *restrict sig);
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20 The sigwait() function shall select a pending signal from set, atomi‐
21 cally clear it from the system's set of pending signals, and return
22 that signal number in the location referenced by sig. If prior to the
23 call to sigwait() there are multiple pending instances of a single sig‐
24 nal number, it is implementation-defined whether upon successful return
25 there are any remaining pending signals for that signal number. If the
26 implementation supports queued signals and there are multiple signals
27 queued for the signal number selected, the first such queued signal
28 shall cause a return from sigwait() and the remainder shall remain
29 queued. If no signal in set is pending at the time of the call, the
30 thread shall be suspended until one or more becomes pending. The sig‐
31 nals defined by set shall have been blocked at the time of the call to
32 sigwait(); otherwise, the behavior is undefined. The effect of sig‐
33 wait() on the signal actions for the signals in set is unspecified.
34 If more than one thread is using sigwait() to wait for the same signal,
36 no more than one of these threads shall return from sigwait() with the
37 signal number. If more than a single thread is blocked in sigwait() for
38 a signal when that signal is generated for the process, it is unspeci‐
39 fied which of the waiting threads returns from sigwait(). If the sig‐
40 nal is generated for a specific thread, as by pthread_kill(), only that
41 thread shall return.
42 Should any of the multiple pending signals in the range SIGRTMIN to
44 SIGRTMAX be selected, it shall be the lowest numbered one. The selec‐
45 tion order between realtime and non-realtime signals, or between multi‐
46 ple pending non-realtime signals, is unspecified.
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49 Upon successful completion, sigwait() shall store the signal number of
50 the received signal at the location referenced by sig and return zero.
51 Otherwise, an error number shall be returned to indicate the error.
52
54 The sigwait() function may fail if:
55 EINVAL The set argument contains an invalid or unsupported signal num‐
57 ber.
58 The following sections are informative.
60
62 None.
63
65 None.
66
68 To provide a convenient way for a thread to wait for a signal, this
69 volume of POSIX.1‐2017 provides the sigwait() function. For most cases
70 where a thread has to wait for a signal, the sigwait() function should
71 be quite convenient, efficient, and adequate.
72 However, requests were made for a lower-level primitive than sigwait()
74 and for semaphores that could be used by threads. After some considera‐
75 tion, threads were allowed to use semaphores and sem_post() was defined
76 to be async-signal-safe.
77 In summary, when it is necessary for code run in response to an asyn‐
79 chronous signal to notify a thread, sigwait() should be used to handle
80 the signal. Alternatively, if the implementation provides semaphores,
81 they also can be used, either following sigwait() or from within a sig‐
82 nal handling routine previously registered with sigaction().
83
85 None.
86
88 Section 2.4, Signal Concepts, Section 2.8.1, Realtime Signals, pause(),
89 pthread_sigmask(), sigaction(), sigpending(), sigsuspend(), sigtimed‐
90 wait()
91 The Base Definitions volume of POSIX.1‐2017, <signal.h>, <time.h>
93
95 Portions of this text are reprinted and reproduced in electronic form
96 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
97 table Operating System Interface (POSIX), The Open Group Base Specifi‐
98 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
99 Electrical and Electronics Engineers, Inc and The Open Group. In the
100 event of any discrepancy between this version and the original IEEE and
101 The Open Group Standard, the original IEEE and The Open Group Standard
102 is the referee document. The original Standard can be obtained online
103 at http://www.opengroup.org/unix/online.html .
104 Any typographical or formatting errors that appear in this page are
106 most likely to have been introduced during the conversion of the source
107 files to man page format. To report such errors, see https://www.ker‐
108 nel.org/doc/man-pages/reporting_bugs.html .
109IEEE/The Open Group 2017 SIGWAIT(3P)