sigtimedwait

SIGWAITINFO(2)             Linux Programmer's Manual            SIGWAITINFO(2)



NAME
       sigwaitinfo, sigtimedwait, rt_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 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;         /* 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, POSIX.1-2008.

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 5.04 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/.




Linux                             2017-09-15                    SIGWAITINFO(2)