1sigwaitinfo(2) System Calls Manual sigwaitinfo(2)
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6 sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait for
7 queued signals
8
10 Standard C library (libc, -lc)
11
13 #include <signal.h>
14 int sigwaitinfo(const sigset_t *restrict set,
16 siginfo_t *_Nullable restrict info);
17 int sigtimedwait(const sigset_t *restrict set,
18 siginfo_t *_Nullable restrict info,
19 const struct timespec *restrict timeout);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 sigwaitinfo(), sigtimedwait():
24 _POSIX_C_SOURCE >= 199309L
25
27 sigwaitinfo() suspends execution of the calling thread until one of the
28 signals in set is pending (If one of the signals in set is already
29 pending for the calling thread, sigwaitinfo() will return immediately.)
30 sigwaitinfo() removes the signal from the set of pending signals and
32 returns the signal number as its function result. If the info argument
33 is not NULL, then the buffer that it points to is used to return a
34 structure of type siginfo_t (see sigaction(2)) containing information
35 about the signal.
36 If multiple signals in set are pending for the caller, the signal that
38 is retrieved by sigwaitinfo() is determined according to the usual or‐
39 dering rules; see signal(7) for further details.
40 sigtimedwait() operates in exactly the same way as sigwaitinfo() except
42 that it has an additional argument, timeout, which specifies the inter‐
43 val for which the thread is suspended waiting for a signal. (This in‐
44 terval will be rounded up to the system clock granularity, and kernel
45 scheduling delays mean that the interval may overrun by a small
46 amount.) This argument is a timespec(3) structure.
47 If both fields of this structure are specified as 0, a poll is per‐
49 formed: sigtimedwait() returns immediately, either with information
50 about a signal that was pending for the caller, or with an error if
51 none of the signals in set was pending.
52
54 On success, both sigwaitinfo() and sigtimedwait() return a signal num‐
55 ber (i.e., a value greater than zero). On failure both calls return
56 -1, with errno set to indicate the error.
57
59 EAGAIN No signal in set became pending within the timeout period speci‐
60 fied to sigtimedwait().
61 EINTR The wait was interrupted by a signal handler; see signal(7).
63 (This handler was for a signal other than one of those in set.)
64 EINVAL timeout was invalid.
66
68 C library/kernel differences
69 On Linux, sigwaitinfo() is a library function implemented on top of
70 sigtimedwait().
71 The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
73 silently ignore attempts to wait for the two real-time signals that are
74 used internally by the NPTL threading implementation. See nptl(7) for
75 details.
76 The original Linux system call was named sigtimedwait(). However, with
78 the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
79 sigset_t type supported by that system call was no longer fit for pur‐
80 pose. Consequently, a new system call, rt_sigtimedwait(), was added to
81 support an enlarged sigset_t type. The new system call takes a fourth
82 argument, size_t sigsetsize, which specifies the size in bytes of the
83 signal set in set. This argument is currently required to have the
84 value sizeof(sigset_t) (or the error EINVAL results). The glibc sig‐
85 timedwait() wrapper function hides these details from us, transparently
86 calling rt_sigtimedwait() when the kernel provides it.
87
89 POSIX.1-2008.
90
92 POSIX.1-2001.
93
95 In normal usage, the calling program blocks the signals in set via a
96 prior call to sigprocmask(2) (so that the default disposition for these
97 signals does not occur if they become pending between successive calls
98 to sigwaitinfo() or sigtimedwait()) and does not establish handlers for
99 these signals. In a multithreaded program, the signal should be
100 blocked in all threads, in order to prevent the signal being treated
101 according to its default disposition in a thread other than the one
102 calling sigwaitinfo() or sigtimedwait()).
103 The set of signals that is pending for a given thread is the union of
105 the set of signals that is pending specifically for that thread and the
106 set of signals that is pending for the process as a whole (see sig‐
107 nal(7)).
108 Attempts to wait for SIGKILL and SIGSTOP are silently ignored.
110 If multiple threads of a process are blocked waiting for the same sig‐
112 nal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of the
113 threads will actually receive the signal if it becomes pending for the
114 process as a whole; which of the threads receives the signal is inde‐
115 terminate.
116 sigwaitinfo() or sigtimedwait(), can't be used to receive signals that
118 are synchronously generated, such as the SIGSEGV signal that results
119 from accessing an invalid memory address or the SIGFPE signal that re‐
120 sults from an arithmetic error. Such signals can be caught only via
121 signal handler.
122 POSIX leaves the meaning of a NULL value for the timeout argument of
124 sigtimedwait() unspecified, permitting the possibility that this has
125 the same meaning as a call to sigwaitinfo(), and indeed this is what is
126 done on Linux.
127
129 kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2), sigproc‐
130 mask(2), sigqueue(3), sigsetops(3), sigwait(3), timespec(3), signal(7),
131 time(7)
132Linux man-pages 6.05 2023-03-30 sigwaitinfo(2)