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 delivered. (If one of the signals in set is already
pending for the calling thread, sigwaitinfo() will return immediately
with information about that signal.)
sigwaitinfo() removes the delivered signal from the set of pending
signals and returns the signal number as its function result. If the
info argument is not NULL, then it returns a structure of type
siginfo_t (see sigaction(2)) containing information about the signal.
Signals returned via sigwaitinfo() are delivered in the usual order;
see signal(7) for further details.
sigtimedwait() operates in exactly the same way as sigwaitinfo() except
that it has an additional argument, timeout, which enables an upper
bound to be placed on the time for which the thread is suspended. 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 delivered 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 are delivered 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 to prevent the signal being delivered to 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)).
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 is delivered to 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(2), sigsetops(3), sigwait(3), signal(7),
time(7)
COLOPHON
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