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 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.

   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
   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 4.09 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/.





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