SIGWAITINFO(2)            (2017-09-15)             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

     Page 1                        Linux             (printed 5/24/22)

     SIGWAITINFO(2)            (2017-09-15)             SIGWAITINFO(2)

          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

     Page 2                        Linux             (printed 5/24/22)

     SIGWAITINFO(2)            (2017-09-15)             SIGWAITINFO(2)

          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 pos-
          sibility 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 5.10 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/.

     Page 3                        Linux             (printed 5/24/22)