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       sigwaitinfo,  sigtimedwait,  rt_sigtimedwait  -  synchronously wait for
       queued signals


       #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


       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.


       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.


       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.


       POSIX.1-2001, POSIX.1-2008.


       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

       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

       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

       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

       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.


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


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