From: Christopher Allan Webber Date: Sun, 1 Jan 2017 14:57:01 +0000 (-0600) Subject: docs: Added "Writing our own actors" section X-Git-Tag: v0.4.0~41 X-Git-Url: https://jxself.org/git/?a=commitdiff_plain;h=7e29f7cd7cda3e2ee56af25917a375d2237355b7;p=8sync.git docs: Added "Writing our own actors" section * doc/8sync-new-manual.org: New "Writing our own actors and sending messages between them" section. --- diff --git a/doc/8sync-new-manual.org b/doc/8sync-new-manual.org index f825e3c..e85b639 100644 --- a/doc/8sync-new-manual.org +++ b/doc/8sync-new-manual.org @@ -552,7 +552,224 @@ IRC> /query examplebot Horray! -** Battle bot! +** Writing our own actors and sending messages between them + +Let's write the most basic, boring actor possible. +How about an actor that start sleeping, and keeps sleeping? + +#+BEGIN_SRC scheme + (use-modules (oop goops) + (8sync)) + + (define-class () + (actions #:allocation #:each-subclass + #:init-value (build-actions + (loop sleeper-loop)))) + + (define (sleeper-loop actor message) + (while (actor-am-i-alive? actor) + (display "Zzzzzzzz....\n") + ;; Sleep for one second + (8sleep 1))) + + (let* ((hive (make-hive)) + (sleeper (hive-create-actor hive ))) + (ez-run-hive hive (list (bootstrap-message hive sleeper 'loop)))) +#+END_SRC + +We see some particular things in this example. +One thing is that our actor has an actions slot. +This is used to look up what the "action handler" for a message is. +We have to set the #:allocation to either #:each-subclass or #:class. +(#:class should be fine, except there is [[https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25211][a bug in Guile]] which keeps +us from using it for now.) + +In our sleeper-loop we also see a call to "8sleep". +"8sleep" is like Guile's "sleep" method, except it is non-blocking +and will always yield to the scheduler. + +Our while loop also checks "actor-am-i-alive?" to see whether or not +it is still registered. +In general, if you keep a loop in your actor that regularly yields +to the scheduler, you should check this. +(An alternate way to handle it would be to not use a while loop at all +but simply send a message to ourselves with "<-" to call the +sleeper-loop handler again. +If the actor was dead, the message simply would not be delivered and +thus the loop would stop.) + +This actor is pretty lazy though. +Time to get back to work! + +#+BEGIN_SRC scheme + (use-modules (8sync) + (oop goops)) + + (define-class () + (direct-report #:init-keyword #:direct-report + #:getter manager-direct-report) + (actions #:allocation #:each-subclass + #:init-value (build-actions + (assign-task manager-assign-task)))) + + (define (manager-assign-task manager message difficulty) + "Delegate a task to our direct report" + (display "manager> Work on this task for me!\n") + (<- manager (manager-direct-report manager) + 'work-on-this difficulty)) +#+END_SRC + +Here we're constructing a very simple manager actor. +This manager keeps track of a direct report and tells them to start +working on a task... simple delegation. +Nothing here is really new, but note that our friend "<-" (which means +"send message") is back. +There's one difference this time... the first time we saw "<-" was in +the handle-line procedure of the irc-bot, and in that case we explicitly +pulled the actor-id after the actor we were sending the message to +(ourselves), which we aren't doing here. +But that was an unusual case, because the actor was ourself. +In this case, and in general, actors don't have direct references to +other actors; instead, all they have is access to identifiers which +reference other actors. + +#+BEGIN_SRC scheme + (define-class () + (task-left #:init-keyword #:task-left + #:accessor worker-task-left) + (actions #:allocation #:each-subclass + #:init-value (build-actions + (work-on-this worker-work-on-this)))) + + (define (worker-work-on-this worker message difficulty) + "" + (set! (worker-task-left worker) difficulty) + (display "worker> Whatever you say, boss!\n") + (while (and (actor-am-i-alive? worker) + (> (worker-task-left worker) 0)) + (display "worker> *huff puff*\n") + (set! (worker-task-left worker) + (- (worker-task-left worker) 1)) + (8sync (/ 1 3))) + (display "worker> Looks like I'm done! Can I go home yet?\n")) +#+END_SRC + +The worker also contains familiar code, but we now see that we can +call 8sync with non-integer real numbers. + +Looks like there's nothing left to do but run it: + +#+BEGIN_SRC scheme + (let* ((hive (make-hive)) + (worker (hive-create-actor hive )) + (manager (hive-create-actor hive + #:direct-report worker))) + (ez-run-hive hive (list (bootstrap-message hive manager 'assign-task 5)))) +#+END_SRC + +#+BEGIN_SRC text +manager> Work on this task for me! +worker> Whatever you say, boss! +worker> *huff puff* +worker> *huff puff* +worker> *huff puff* +worker> *huff puff* +worker> *huff puff* +worker> Looks like I'm done! Can I go home yet? +#+END_SRC + +"<-" pays no attention to what happens with the messages it has sent +off. +This is useful in many cases... we can blast off many messages and +continue along without holding anything back. + +But sometimes we want to make sure that something completes before +we do something else, or we want to send a message and get some sort +of information back. +Luckily 8sync comes with an answer to that with "<-wait", which will +suspend the caller until the callee gives some sort of response, but +which does not block the rest of the program from running. +Let's try applying that to our own code by turning our manager +into a micromanager. + +#+END_SRC +#+BEGIN_SRC scheme + ;;; Update this method + (define (manager-assign-task manager message difficulty) + "Delegate a task to our direct report" + (display "manager> Work on this task for me!\n") + (<- manager (manager-direct-report manager) + 'work-on-this difficulty) + + ;; call the micromanagement loop + (manager-micromanage-loop manager)) + + ;;; And add the following + ;;; (... Note: do not model actual employee management off this) + (define (manager-micromanage-loop manager) + "Pester direct report until they're done with their task." + (display "manager> Are you done yet???\n") + (let ((still-working + (msg-val (<-wait manager (manager-direct-report manager) + 'done-yet?)))) + (if still-working + (begin (display "manager> Harumph!\n") + (8sleep 1) + (when (actor-am-i-alive? manager) + (manager-micromanage-loop manager))) + (begin (display "manager> Oh! I guess you can go home then.\n") + (<- manager (manager-direct-report manager) 'go-home))))) +#+END_SRC + +We've appended a micromanagement loop here... but what's going on? +"<-wait", as it sounds, waits for a reply, and returns a reply +message. +In this case there's a value in the body of the message we want, +so we pull it out with msg-val. +(It's possible for a remote actor to return multiple values, in which +case we'd want to use msg-receive, but that's a bit more complicated.) + +Of course, we need to update our worker accordingly as well. + +#+BEGIN_SRC scheme + ;;; Update the worker to add the following new actions: + (define-class () + (task-left #:init-keyword #:task-left + #:accessor worker-task-left) + (actions #:allocation #:each-subclass + #:init-value (build-actions + (work-on-this worker-work-on-this) + ;; Add these: + (done-yet? worker-done-yet?) + (go-home worker-go-home)))) + + ;;; New procedures: + (define (worker-done-yet? worker message) + "Reply with whether or not we're done yet." + (<-reply worker message + (= (worker-task-left worker) 0))) + + (define (worker-go-home worker message) + "It's off of work for us!" + (display "worker> Whew! Free at last.") + (self-destruct worker)) +#+END_SRC + +"<-reply" is what actually returns the information to the actor +waiting on the reply. +It takes as an argument the actor sending the message, the message +it is in reply to, and the rest of the arguments are the "body" of +the message. +(If an actor handles a message that is being "waited on" but does not +explicitly reply to it, an auto-reply with an empty body will be +triggered so that the waiting actor is not left waiting around.) + +The last thing to note is the call to "self-destruct". +This does what you might expect: it removes the actor from the hive. +No new messages will be sent to it. +Ka-poof! + +** Extended example: an IRC bot battle ** Adding a "rankings" web page