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poll results
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SIGWAITINFO
Section: Linux Programmer's Manual (2)
Updated: 2012-07-21
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NAME
sigwaitinfo, sigtimedwait - synchronously wait for queued signals
SYNOPSIS
#include <signal.h>
int sigwaitinfo(const sigset_t *set, siginfo_t *info);
int sigtimedwait(const sigset_t *set, siginfo_t *info,
const struct timespec *timeout);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
sigwaitinfo(),
sigtimedwait():
_POSIX_C_SOURCE >= 199309L
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 a minimum 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; /* seconds */
long tv_nsec; /* nanoseconds */
}
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
set
was 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.
CONFORMING TO
POSIX.1-2001.
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.
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.
On Linux,
sigwaitinfo()
is a library function implemented on top of
sigtimedwait().
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 3.42 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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