




Reads the next object in a mailbox.
The function mailbox-read returns the next object from the mailbox mailbox, or nil.
If mailbox is empty and timeout is nil, then mailbox-read blocks until an object is placed in mailbox. If mailbox is empty and timeout is a non-negative real, then mailbox-read blocks until an object is placed in mailbox or timeout seconds have passed. If the timeout occurs, then mailbox-read returns nil as the first value and also flag is nil. If an object is actually read from the mailbox, then flag is t.
The wait-reason argument defaults to "Waiting for message in #<Mailbox...>" and will be the value returned by process-whostate while mailbox-read is blocking.
mailbox-empty-p
mailbox-peek
mailbox-send
mailbox-wait-for-event
make-mailbox
Communication between processes and synchronization
LispWorks User Guide and Reference Manual - 20 Sep 2017