adds the message pointed to by
to the message queue referred to by the descriptor
argument specifies the length of the message pointed to by
this length must be less than or equal to the queue's
Zero-length messages are allowed.
argument is a nonnegative integer that specifies the priority
of this message.
Messages are placed on the queue in decreasing order of priority,
with newer messages of the same priority being placed after
older messages with the same priority.
If the message queue is already full
(i.e., the number of messages on the queue equals the queue's
attribute), then, by default,
blocks until sufficient space becomes available to allow the message
to be queued, or until the call is interrupted by a signal handler.
flag is enabled for the message queue description,
then the call instead fails immediately with the error
behaves just like
except that if the queue is full and the
flag is not enabled for the message queue description, then
points to a structure which specifies a ceiling on the time for which
the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds
since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), and it is
specified in the following structure: