This is a very, very trivial implementation of channels (and a queue). I find myself using it in a few places where very trivial message passing is needed and a more complex, robust solution would be overkill.
(let ((channel (make-channel))) (sendmsg channel 'anything) (recvmsg channel)) ;; => ANYTHING
(make-channel): Make a channel
(sendmsg CHANNEL OBJECT): Send
(recvmsg CHANNEL &optional TIMEOUT): Receive on
CHANNEL, optionally timing out after
(getmsg CHANNEL): Get a message if available, or
(hasmsg CHANNEL): Whether the channel has a message. No guarantee it will still have one after the call, if there are multiple receivers sharing a channel.
recvmsg supports a timeout. These functions properly lock and it's safe to share a channel between threads (that being the entire purpose).
While trivial-channels should be simple enough you can adapt it to many usage patterns, for simple bi-directional message passing I have found it easiest to simply pass a message with a return-channel included:
;;; Sender: (defvar *global-listener* (make-channel)) (defvar *done* nil) (let* ((return-channel (make-channel)) (msg (cons 'value return-channel))) (sendmsg *global-listener* msg) (recvmsg return-channel)) ;;; Meanwhile, in another thread: (loop until *done* do (let ((msg (recvmsg *global-listener*))) (let ((value (car msg)) (channel (cdr msg))) ;; insert useful things here (sendmsg channel ...))))
Of course, you needn't create a new return channel every time, either, if you are worried about consing, but this is an easy way to pass functions to a specific thread, implement actors, etc.
The queue used to implement this is also available via the package
:trivial-channels.queue, since it's sometimes handy to have a trivial queue, too.
Queues do not lock.
Queues are implemented with conses.
(make-queue): Make a queue
(queue-head Q): Head of the queue
(queue-tail Q): Tail of the queue
(queue-add-cons Q CONS):
CONSbecomes the tail of the queue; its CDR may be destructively modified
(queue-add Q ITEM): Add
ITEMto the tail of the queue
(queue-push Q ITEM): Push
ITEMonto the front of the queue
(queue-pop Q): Pop and return and item from the queue, or NIL
(queue-pop-cons Q): Pop and return the cons from the queue, or NIL
(queue-has-item-p Q): If there are items in the queue, or NIL
(queue-peek Q): The front item in the queue, or NIL
(queue-pop-to Q1 Q2): Pop an item from
Q1and add it to
(queue-prepend-to Q1 Q2): Remove all items from
Q1and prepend them to
Q2without consing; no value returned
All add or remove type operations return the item (or cons) being handled, unless otherwise noted.
- Ryan Pavlik