Name
sigwaitinfo, sigtimedwait, rt_sigtimedwait — synchronously wait for queued signals
Synopsis
#include <signal.h>
int
sigwaitinfo( |
const sigset_t *restrict set, |
siginfo_t *restrict info); |
int
sigtimedwait( |
const sigset_t *restrict set, |
| siginfo_t *restrict info, | |
const struct timespec *restrict timeout); |
![[Note]](../stylesheet/note.png) |
Note | ||
|---|---|---|---|
|
DESCRIPTION
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 of
the following type:
struct timespec { long tv_sec;long tv_nsec;};
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.
RETURN VALUE
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.
ERRORS
- EAGAIN
-
No signal in
setbecame pending within thetimeoutperiod specified tosigtimedwait(). - 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
-
timeoutwas invalid.
NOTES
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.
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.
SEE ALSO
kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2), sigprocmask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7), time(7)
COLOPHON
This page is part of release 5.13 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 2002 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |