|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
|
|
|
sigwaitinfo(2) System Calls Manual sigwaitinfo(2)
sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait
for queued signals
Standard C library (libc, -lc)
#include <signal.h>
int sigwaitinfo(const sigset_t *restrict set,
siginfo_t *_Nullable restrict info);
int sigtimedwait(const sigset_t *restrict set,
siginfo_t *_Nullable restrict info,
const struct timespec *restrict timeout);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
sigwaitinfo(), sigtimedwait():
_POSIX_C_SOURCE >= 199309L
sigwaitinfo() suspends execution of the calling thread until one
of the signals in set is pending (If one of the signals in set is
already pending for the calling thread, sigwaitinfo() will return
immediately.)
sigwaitinfo() removes the signal from the set of pending signals
and returns the signal number as its function result. If the info
argument is not NULL, then the buffer that it points to is used to
return a structure of type siginfo_t (see sigaction(2)) containing
information about the signal.
If multiple signals in set are pending for the caller, the signal
that is retrieved by sigwaitinfo() is determined according to the
usual ordering rules; see signal(7) for further details.
sigtimedwait() operates in exactly the same way as sigwaitinfo()
except that it has an additional argument, timeout, which
specifies the interval for which the thread is suspended waiting
for a signal. (This interval will be rounded up to the system
clock granularity, and kernel scheduling delays mean that the
interval may overrun by a small amount.) This argument is a
timespec(3) structure.
If both fields of this structure are specified as 0, a poll is
performed: sigtimedwait() returns immediately, either with
information about a signal that was pending for the caller, or
with an error if none of the signals in set was pending.
On success, both sigwaitinfo() and sigtimedwait() return a signal
number (i.e., a value greater than zero). On failure both calls
return -1, with errno set to indicate the error.
EAGAIN No signal in set became pending within the timeout period
specified to sigtimedwait().
EINTR The wait was interrupted by a signal handler; see
signal(7). (This handler was for a signal other than one
of those in set.)
EINVAL timeout was invalid.
C library/kernel differences
On Linux, sigwaitinfo() is a library function implemented on top
of sigtimedwait().
The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
silently ignore attempts to wait for the two real-time signals
that are used internally by the NPTL threading implementation.
See nptl(7) for details.
The original Linux system call was named sigtimedwait(). However,
with the addition of real-time signals in Linux 2.2, the fixed-
size, 32-bit sigset_t type supported by that system call was no
longer fit for purpose. Consequently, a new system call,
rt_sigtimedwait(), was added to support an enlarged sigset_t type.
The new system call takes a fourth argument, size_t sigsetsize,
which specifies the size in bytes of the signal set in set. This
argument is currently required to have the value sizeof(sigset_t)
(or the error EINVAL results). The glibc sigtimedwait() wrapper
function hides these details from us, transparently calling
rt_sigtimedwait() when the kernel provides it.
POSIX.1-2008.
POSIX.1-2001.
In normal usage, the calling program blocks the signals in set via
a prior call to sigprocmask(2) (so that the default disposition
for these signals does not occur if they become pending between
successive calls to sigwaitinfo() or sigtimedwait()) and does not
establish handlers for these signals. In a multithreaded program,
the signal should be blocked in all threads, in order to prevent
the signal being treated according to its default disposition in a
thread other than the one calling sigwaitinfo() or
sigtimedwait()).
The set of signals that is pending for a given thread is the union
of the set of signals that is pending specifically for that thread
and the set of signals that is pending for the process as a whole
(see signal(7)).
Attempts to wait for SIGKILL and SIGSTOP are silently ignored.
If multiple threads of a process are blocked waiting for the same
signal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of
the threads will actually receive the signal if it becomes pending
for the process as a whole; which of the threads receives the
signal is indeterminate.
sigwaitinfo() or sigtimedwait(), can't be used to receive signals
that are synchronously generated, such as the SIGSEGV signal that
results from accessing an invalid memory address or the SIGFPE
signal that results from an arithmetic error. Such signals can be
caught only via signal handler.
POSIX leaves the meaning of a NULL value for the timeout argument
of sigtimedwait() unspecified, permitting the possibility that
this has the same meaning as a call to sigwaitinfo(), and indeed
this is what is done on Linux.
kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2),
sigprocmask(2), sigqueue(3), sigsetops(3), sigwait(3),
timespec(3), signal(7), time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 sigwaitinfo(2)
Pages that refer to this page: clone(2), signalfd(2), sigsuspend(2), syscalls(2), timer_getoverrun(2), sigevent(3type), sigqueue(3), sigwait(3), nptl(7), signal(7), system_data_types(7), time(7)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|