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       sigwaitinfo, 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 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.


       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  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.




       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

       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 is delivered to 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.

       On Linux, sigwaitinfo() is a library function  implemented  on  top  of


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


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