system call causes the signal specified by
to be sent with the value specified by
to the process specified by
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
system call queues a signal to a single process specified by the
system call returns immediately.
If the resources were
available to queue the signal, the signal will be queued and sent to
the receiving process.
If the value of
to be generated for the sending process, and if
is not blocked for the calling thread and if no other thread has
unblocked or is waiting in a
system call for
or at least the pending, unblocked signal will be delivered to the
calling thread before
Should any multiple pending signals in the range
be selected for delivery, it is the lowest numbered
The selection order between realtime and non-realtime signals, or
between multiple pending non-realtime signals, is unspecified.