sigwaitinfo(2) — Linux manual page


sigwaitinfo(2)             System Calls Manual            sigwaitinfo(2)

NAME         top

       sigwaitinfo, sigtimedwait, rt_sigtimedwait - synchronously wait
       for queued signals

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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

       sigwaitinfo(), sigtimedwait():
           _POSIX_C_SOURCE >= 199309L

DESCRIPTION         top

       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

       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.

RETURN VALUE         top

       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         top

       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.

VERSIONS         top

   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

STANDARDS         top


HISTORY         top


NOTES         top

       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.

SEE ALSO         top

       kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2),
       sigprocmask(2), sigqueue(3), sigsetops(3), sigwait(3),
       timespec(3), signal(7), time(7)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                 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)