sigqueue(2)                                                     sigqueue(2)




 NAME    [Toc]    [Back]
      sigqueue() - queue a signal to a process

 SYNOPSIS    [Toc]    [Back]
      #include <signal.h>

      int sigqueue(pid_t pid, int signo, const union sigval value);

 DESCRIPTION    [Toc]    [Back]
      The sigqueue() system call causes the signal specified by signo to be
      sent with the value specified by value to the process specified by
      pid.  If signo is zero (the null signal), error checking is performed
      but no signal is actually sent. The null signal can be used to check
      the validity of pid.

      The conditions required for a process to have permission to queue a
      signal to another process are the same as for the kill() system call.

      The sigqueue() system call returns immediately.  If SA_SIGINFO is set
      for signo at the receiving process (see sigqueue(2)) and if resources
      are available to queue the signal, the signal will be queued and sent
      to the receiving process.  When the signal is delivered or accepted,
      the field si_value of the siginfo parameter (see signal(5)) will be
      set to value.  If SA_SIGINFO is not set for signo, then signo, but not
      necessarily value, will be sent at least once to the receiving
      process.

      If the value of pid causes signo to be generated for the sending
      process, and if signo is not blocked, either signo or at least one
      pending unblocked signal will be delivered to the sending process
      before the sigqueue() system call returns.  Should any of multiple
      pending signals in the range SIGRTMIN to SIGRTMAX be selected for
      delivery or acceptance, it will be the lowest numbered one.  The
      selection order between realtime and non-realtime signals, or between
      multiple pending non-realtime signals, is unspecified.

    Application Usage    [Toc]    [Back]
      Threads Considerations

      sigqueue() can be used to post signals to another process but can not
      be used to post signals to a specific thread in another process.

      If the value of pid causes signo to be generated for the sending
      process, and if signo is not blocked for the calling thread and if no
      other thread has signo unblocked or is waiting in a sigwait() function
      for signo, either signo or at least one pending unblocked signal will
      be delivered to the calling thread before the sigqueue() function
      returns.

      LWP Considerations    [Toc]    [Back]




 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 sigqueue(2)                                                     sigqueue(2)




      Signals can not be posted to specific Lightweight Processes (LWPs) in
      another process.

 RETURN VALUE    [Toc]    [Back]
      Upon successful completion, the specified signal will be queued, and
      the sigqueue() function returns a value of 0 (zero).  Otherwise, a
      value of -1 is returned, and errno is set to indicate the error.

 ERRORS    [Toc]    [Back]
      sigqueue() fails and no signal is sent if any of the following
      conditions occur:

           [EAGAIN]       No resources are available to queue the signal.
                          The process has already queued {SIGQUEUE_MAX}
                          signals that are still pending at the receiver(s),
                          or a systemwide resource limit has been exceeded.

           [EINVAL]       The value of the signo argument is an invalid or
                          unsupported signal number.

           [EPERM]        The process does not have the appropriate
                          privilege to send the signal to the receiving
                          process.

           [ESRCH]        The process pid does not exist.

 SEE ALSO    [Toc]    [Back]
      kill(2), sysconf(2), signal(5).


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003