1SIGWAITINFO(2) Linux Programmer's Manual SIGWAITINFO(2)
2
6 sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait for
7 queued signals
8
10 #include <signal.h>
11 int sigwaitinfo(const sigset_t *restrict set,
13 siginfo_t *restrict info);
14 int sigtimedwait(const sigset_t *restrict set,
15 siginfo_t *restrict info,
16 const struct timespec *restrict timeout);
17 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
19 sigwaitinfo(), sigtimedwait():
21 _POSIX_C_SOURCE >= 199309L
22
24 sigwaitinfo() suspends execution of the calling thread until one of the
25 signals in set is pending (If one of the signals in set is already
26 pending for the calling thread, sigwaitinfo() will return immediately.)
27 sigwaitinfo() removes the signal from the set of pending signals and
29 returns the signal number as its function result. If the info argument
30 is not NULL, then the buffer that it points to is used to return a
31 structure of type siginfo_t (see sigaction(2)) containing information
32 about the signal.
33 If multiple signals in set are pending for the caller, the signal that
35 is retrieved by sigwaitinfo() is determined according to the usual or‐
36 dering rules; see signal(7) for further details.
37 sigtimedwait() operates in exactly the same way as sigwaitinfo() except
39 that it has an additional argument, timeout, which specifies the inter‐
40 val for which the thread is suspended waiting for a signal. (This in‐
41 terval will be rounded up to the system clock granularity, and kernel
42 scheduling delays mean that the interval may overrun by a small
43 amount.) This argument is of the following type:
44 struct timespec {
46 long tv_sec; /* seconds */
47 long tv_nsec; /* nanoseconds */
48 }
49 If both fields of this structure are specified as 0, a poll is per‐
51 formed: sigtimedwait() returns immediately, either with information
52 about a signal that was pending for the caller, or with an error if
53 none of the signals in set was pending.
54
56 On success, both sigwaitinfo() and sigtimedwait() return a signal num‐
57 ber (i.e., a value greater than zero). On failure both calls return
58 -1, with errno set to indicate the error.
59
61 EAGAIN No signal in set became pending within the timeout period speci‐
62 fied to sigtimedwait().
63 EINTR The wait was interrupted by a signal handler; see signal(7).
65 (This handler was for a signal other than one of those in set.)
66 EINVAL timeout was invalid.
68
70 POSIX.1-2001, POSIX.1-2008.
71
73 In normal usage, the calling program blocks the signals in set via a
74 prior call to sigprocmask(2) (so that the default disposition for these
75 signals does not occur if they become pending between successive calls
76 to sigwaitinfo() or sigtimedwait()) and does not establish handlers for
77 these signals. In a multithreaded program, the signal should be
78 blocked in all threads, in order to prevent the signal being treated
79 according to its default disposition in a thread other than the one
80 calling sigwaitinfo() or sigtimedwait()).
81 The set of signals that is pending for a given thread is the union of
83 the set of signals that is pending specifically for that thread and the
84 set of signals that is pending for the process as a whole (see sig‐
85 nal(7)).
86 Attempts to wait for SIGKILL and SIGSTOP are silently ignored.
88 If multiple threads of a process are blocked waiting for the same sig‐
90 nal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of the
91 threads will actually receive the signal if it becomes pending for the
92 process as a whole; which of the threads receives the signal is inde‐
93 terminate.
94 sigwaitinfo() or sigtimedwait(), can't be used to receive signals that
96 are synchronously generated, such as the SIGSEGV signal that results
97 from accessing an invalid memory address or the SIGFPE signal that re‐
98 sults from an arithmetic error. Such signals can be caught only via
99 signal handler.
100 POSIX leaves the meaning of a NULL value for the timeout argument of
102 sigtimedwait() unspecified, permitting the possibility that this has
103 the same meaning as a call to sigwaitinfo(), and indeed this is what is
104 done on Linux.
105 C library/kernel differences
107 On Linux, sigwaitinfo() is a library function implemented on top of
108 sigtimedwait().
109 The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
111 silently ignore attempts to wait for the two real-time signals that are
112 used internally by the NPTL threading implementation. See nptl(7) for
113 details.
114 The original Linux system call was named sigtimedwait(). However, with
116 the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
117 sigset_t type supported by that system call was no longer fit for pur‐
118 pose. Consequently, a new system call, rt_sigtimedwait(), was added to
119 support an enlarged sigset_t type. The new system call takes a fourth
120 argument, size_t sigsetsize, which specifies the size in bytes of the
121 signal set in set. This argument is currently required to have the
122 value sizeof(sigset_t) (or the error EINVAL results). The glibc sig‐
123 timedwait() wrapper function hides these details from us, transparently
124 calling rt_sigtimedwait() when the kernel provides it.
125
127 kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2), sigproc‐
128 mask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7), time(7)
129
131 This page is part of release 5.12 of the Linux man-pages project. A
132 description of the project, information about reporting bugs, and the
133 latest version of this page, can be found at
134 https://www.kernel.org/doc/man-pages/.
135Linux 2021-03-22 SIGWAITINFO(2)