SIGQUEUE(3)                                                        SIGQUEUE(3)


NAME
     sigqueue - queue a signal to a process  (POSIX)

C SYNOPSIS
     #include <signal.h>

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

DESCRIPTION
     The function sigqueue() 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(2) function.

     If the signal specified in signo is currently blocked for the receiving
     process, sigqueue() shall return immediately and, if SA_SIGINFO is set
     for signo and if the resources were available to queue the signal, the
     signal shall be left queued and pending. Furthermore, when the signal
     handler for signo is delivered, the field si_code of the passed in
     siginfo structure will be set to SI_QUEUE (see sigaction(2), signal(5)).
     If SA_SIGINFO is not set for signo, then signo, but not necessarily
     value, shall 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 for the calling thread and if no other thread
     has signo unblocked or is waiting in a sigwait function for signo, at
     least one pending unblocked signal shall be delivered to the calling
     thread before the sigqueue() function returns.

SEE ALSO
     kill(2), sigaction(2), sigwait(3), signal(5).

DIAGNOSTICS
     Upon successful completion, the sigqueue() function returns a value of 0
     indicating that the specified signal has been queued. Otherwise a value
     of -1 is returned and errno is set to indicate the error.  If any of the
     conditions below occur, the sigqueue() function shall return -1 and set
     errno to the corresponding value:

     [EAGAIN]       No resources available to queue the signal.  The process
                    has already queued SIGQUEUE_MAX signals that are still
                    pending at the receivers, or a system wide resource limit
                    has been exceeded.

     [EINVAL]       The value of the sig 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.

WARNING
     The POSIX and System V signal facilities have different semantics.  Using
     both facilities in the same program is strongly discouraged and will
     result in unpredictable behavior.


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