SIGWAITINFO(2)



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

NAME
       sigwaitinfo, 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 inter-
       val  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  per-
       formed:  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 num-
       ber (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.

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  sig-
       nal(7)).

       Attempts to wait for SIGKILL and SIGSTOP are silently ignored.

       If  multiple threads of a process are blocked waiting for the same sig-
       nal(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  inde-
       terminate.

       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 ABI differences
       On Linux, sigwaitinfo() is a library function  implemented  on  top  of
       sigtimedwait().

       The raw sigtimedwait() system call has a fifth argument, size_t sigset-
       size, which specifies the size in bytes of the set argument.  The glibc
       sigtimedwait()  wrapper  function  specifies  this  argument as a fixed
       value (equal to sizeof(sigset_t)).

SEE ALSO
       kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2),  sigproc-
       mask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7), time(7)

COLOPHON
       This  page  is  part of release 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux                             2014-08-19                    SIGWAITINFO(2)

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