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 *set, siginfo_t *info);
13 int sigtimedwait(const sigset_t *set, siginfo_t *info,
15 const struct timespec *timeout);
16 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
18 sigwaitinfo(), sigtimedwait(): _POSIX_C_SOURCE >= 199309L
20
22 sigwaitinfo() suspends execution of the calling thread until one of the
23 signals in set is pending (If one of the signals in set is already
24 pending for the calling thread, sigwaitinfo() will return immediately.)
25 sigwaitinfo() removes the signal from the set of pending signals and
27 returns the signal number as its function result. If the info argument
28 is not NULL, then the buffer that it points to is used to return a
29 structure of type siginfo_t (see sigaction(2)) containing information
30 about the signal.
31 If multiple signals in set are pending for the caller, the signal that
33 is retrieved by sigwaitinfo() is determined according to the usual
34 ordering rules; see signal(7) for further details.
35 sigtimedwait() operates in exactly the same way as sigwaitinfo() except
37 that it has an additional argument, timeout, which specifies the inter‐
38 val for which the thread is suspended waiting for a signal. (This
39 interval will be rounded up to the system clock granularity, and kernel
40 scheduling delays mean that the interval may overrun by a small
41 amount.) This argument is of the following type:
42 struct timespec {
44 long tv_sec; /* seconds */
45 long tv_nsec; /* nanoseconds */
46 }
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 was became pending within the timeout period
60 specified 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 POSIX.1-2001, POSIX.1-2008.
69
71 In normal usage, the calling program blocks the signals in set via a
72 prior call to sigprocmask(2) (so that the default disposition for these
73 signals does not occur if they become pending between successive calls
74 to sigwaitinfo() or sigtimedwait()) and does not establish handlers for
75 these signals. In a multithreaded program, the signal should be
76 blocked in all threads, in order to prevent the signal being treated
77 according to its default disposition in a thread other than the one
78 calling sigwaitinfo() or sigtimedwait()).
79 The set of signals that is pending for a given thread is the union of
81 the set of signals that is pending specifically for that thread and the
82 set of signals that is pending for the process as a whole (see sig‐
83 nal(7)).
84 Attempts to wait for SIGKILL and SIGSTOP are silently ignored.
86 If multiple threads of a process are blocked waiting for the same sig‐
88 nal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of the
89 threads will actually receive the signal if it becomes pending for the
90 process as a whole; which of the threads receives the signal is inde‐
91 terminate.
92 sigwaitinfo() or sigtimedwait(), can't be used to receive signals that
94 are synchronously generated, such as the SIGSEGV signal that results
95 from accessing an invalid memory address or the SIGFPE signal that
96 results from an arithmetic error. Such signals can be caught only via
97 signal handler.
98 POSIX leaves the meaning of a NULL value for the timeout argument of
100 sigtimedwait() unspecified, permitting the possibility that this has
101 the same meaning as a call to sigwaitinfo(), and indeed this is what is
102 done on Linux.
103 C library/kernel differences
105 On Linux, sigwaitinfo() is a library function implemented on top of
106 sigtimedwait().
107 The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
109 silently ignore attempts to wait for the two real-time signals that are
110 used internally by the NPTL threading implementation. See nptl(7) for
111 details.
112 The original Linux system call was named sigtimedwait(). However, with
114 the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit
115 sigset_t type supported by that system call was no longer fit for pur‐
116 pose. Consequently, a new system call, rt_sigtimedwait(), was added to
117 support an enlarged sigset_t type. The new system call takes a fourth
118 argument, size_t sigsetsize, which specifies the size in bytes of the
119 signal set in set. This argument is currently required to have the
120 value sizeof(sigset_t) (or the error EINVAL results). The glibc sig‐
121 timedwait() wrapper function hides these details from us, transparently
122 calling rt_sigtimedwait() when the kernel provides it.
123
125 kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2), sigproc‐
126 mask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7), time(7)
127
129 This page is part of release 4.16 of the Linux man-pages project. A
130 description of the project, information about reporting bugs, and the
131 latest version of this page, can be found at
132 https://www.kernel.org/doc/man-pages/.
133Linux 2017-09-15 SIGWAITINFO(2)