From: Christopher Allan Webber Date: Thu, 5 Jan 2017 03:36:31 +0000 (-0600) Subject: doc: Tutorial additions. X-Git-Tag: v0.4.0~18 X-Git-Url: https://jxself.org/git/?p=8sync.git;a=commitdiff_plain;h=c5626295d8327306833f53d63f41f21bbac7aed6 doc: Tutorial additions. * doc/8sync-new-manual.org: Add "Writing our own network-enabled actor" section. Clean up other sections, including moving the intro to the tutorial blathering about IRC systems to a footnote. --- diff --git a/doc/8sync-new-manual.org b/doc/8sync-new-manual.org index c4cf67e..ec65102 100644 --- a/doc/8sync-new-manual.org +++ b/doc/8sync-new-manual.org @@ -78,43 +78,14 @@ Onward! * Tutorial -** Intro to the tutorial +** A silly little IRC bot IRC! Internet Relay Chat! The classic chat protocol of the Internet. And it turns out, one of the best places to learn about networked -programming. - -In the 1990s I remember stumbling into some funky IRC chat rooms and -being astounded that people there had what they called "bots" hanging -around. -From then until now, I've always enjoyed encountering bots whose range -of functionality has spanned from saying absurd things, to taking -messages when their "owners" were offline, to reporting the weather, -to logging meetings for participants. -And it turns out, IRC bots are a great way to cut your teeth on -networked programming; since IRC is a fairly simple line-delineated -protocol, it's a great way to learn to interact with sockets. -(My first IRC bot helped my team pick a place to go to lunch, previously -a source of significant dispute!) -At the time of writing, venture capital awash startups are trying to -turn chatbots into "big business"... a strange (and perhaps absurd) -thing given chat bots being a fairly mundane novelty amongst hackers -and teenagers everywhere in the 1990s. - +programming.[fn:irc-hacking] We ourselves are going to explore chat bots as a basis for getting our feet wet in 8sync. -We'll start from a minimalist example using an irc bot with most of -the work done for us, then move on to constructing our own actors as -"game pieces" which interface with our bot, then experiment with just -how easy it is to add new networked layers by tacking on a high score -to our game, and as a finale we'll dive into writing our own little -irc bot framework "from scratch" on top of the 8sync actor model. - -Alright, let's get started. -This should be a lot of fun! - -** A silly little IRC bot First of all, we're going to need to import some modules. Put this at the top of your file: @@ -169,7 +140,7 @@ yet. Time to fix that! #+END_SRC Actors are connected to something called a "hive", which is a -special kind of actor that runs all the other actors. +special kind of actor that runs and manages all the other actors. Actors can spawn other actors, but before we start the hive we use this special "bootstrap-actor*" method. It takes the hive as its first argument, the actor class as the second @@ -389,6 +360,24 @@ Take some time to experiment with extending the bot a bit before moving on to the next section! What cool commands can you add? +[fn:irc-hacking] + In the 1990s I remember stumbling into some funky IRC chat rooms and + being astounded that people there had what they called "bots" hanging + around. + From then until now, I've always enjoyed encountering bots whose range + of functionality has spanned from saying absurd things, to taking + messages when their "owners" were offline, to reporting the weather, + to logging meetings for participants. + And it turns out, IRC bots are a great way to cut your teeth on + networked programming; since IRC is a fairly simple line-delineated + protocol, it's a great way to learn to interact with sockets. + (My first IRC bot helped my team pick a place to go to lunch, previously + a source of significant dispute!) + At the time of writing, venture capital awash startups are trying to + turn chatbots into "big business"... a strange (and perhaps absurd) + thing given chat bots being a fairly mundane novelty amongst hackers + and teenagers everywhere in the 1990s. + ** An intermission: about live hacking This section is optional, but highly recommended. @@ -563,17 +552,17 @@ How about an actor that start sleeping, and keeps sleeping? (define-class () (actions #:allocation #:each-subclass #:init-value (build-actions - (loop sleeper-loop)))) + (*init* sleeper-loop)))) (define (sleeper-loop actor message) (while (actor-alive? actor) (display "Zzzzzzzz....\n") - ;; Sleep for one second - (8sleep 1))) + ;; Sleep for one second + (8sleep (sleeper-sleep-secs actor)))) (let* ((hive (make-hive)) (sleeper (bootstrap-actor hive ))) - (run-hive hive (list (bootstrap-message hive sleeper 'loop)))) + (run-hive hive '())) #+END_SRC We see some particular things in this example. @@ -583,6 +572,11 @@ 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.) +The only action handler we've added is for =*init*=, which is called +implicitly when the actor first starts up. +(This will be true whether we bootstrap the actor before the hive +starts or create it during the hive's execution.) + 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. @@ -597,19 +591,42 @@ sleeper-loop handler again. If the actor was dead, the message simply would not be delivered and thus the loop would stop.) +It turns out we could have written the class for the actor much more +simply: + +#+BEGIN_SRC scheme + ;; You could do this instead of the define-class above. + (define-actor () + ((*init* sleeper-loop))) +#+END_SRC + +This is sugar, and expands into exactly the same thing as the +define-class above. +The third argument is an argument list, the same as what's passed +into build-actions. +Everything after that is a slot. +So for example, if we had added an optional slot to specify +how many seconds to sleep, we could have done it like so: + +#+BEGIN_SRC scheme + (define-actor () + ((*init* sleeper-loop)) + (sleep-secs #:init-value 1 + #:getter sleeper-sleep-secs)) +#+END_SRC + This actor is pretty lazy though. Time to get back to work! +Let's build a worker / manager type system. #+BEGIN_SRC scheme (use-modules (8sync) (oop goops)) - (define-class () + (define-actor () + ((assign-task manager-assign-task)) (direct-report #:init-keyword #:direct-report - #:getter manager-direct-report) - (actions #:allocation #:each-subclass - #:init-value (build-actions - (assign-task manager-assign-task)))) + #:getter manager-direct-report)) (define (manager-assign-task manager message difficulty) "Delegate a task to our direct report" @@ -618,7 +635,6 @@ Time to get back to work! '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 @@ -633,12 +649,10 @@ other actors; instead, all they have is access to identifiers which reference other actors. #+BEGIN_SRC scheme - (define-class () + (define-actor () + ((work-on-this worker-work-on-this)) (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)))) + #:accessor worker-task-left)) (define (worker-work-on-this worker message difficulty) "Work on one task until done." @@ -655,7 +669,7 @@ reference other actors. The worker also contains familiar code, but we now see that we can call 8sleep with non-integer real numbers. -Looks like there's nothing left to do but run it: +Looks like there's nothing left to do but run it. #+BEGIN_SRC scheme (let* ((hive (make-hive)) @@ -665,6 +679,9 @@ Looks like there's nothing left to do but run it: (run-hive hive (list (bootstrap-message hive manager 'assign-task 5)))) #+END_SRC +Unlike the ==, our == doesn't have an implicit +=*init*= method, so we've bootstrapped the calling =assign-task= action. + #+BEGIN_SRC text manager> Work on this task for me! worker> Whatever you say, boss! @@ -732,15 +749,13 @@ 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 () + (define-actor () + ((work-on-this worker-work-on-this) + ;; Add these: + (done-yet? worker-done-yet?) + (go-home worker-go-home)) (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)))) + #:accessor worker-task-left)) ;;; New procedures: (define (worker-done-yet? worker message) @@ -807,7 +822,184 @@ This does what you might expect: it removes the actor from the hive. No new messages will be sent to it. Ka-poof! -** Writing our own from scratch +** Writing our own network-enabled actor + +So, you want to write a networked actor! +Well, luckily that's pretty easy, especially with all you know so far. + +#+BEGIN_SRC scheme + (use-modules (oop goops) + (8sync) + (ice-9 rdelim) ; line delineated i/o + (ice-9 match)) ; pattern matching + + (define-actor () + ((*init* telcmd-init) + (*cleanup* telcmd-cleanup) + (new-client telcmd-new-client)) + (socket #:accessor telcmd-socket + #:init-value #f)) +#+END_SRC + +Nothing surprising about the actor definition, though we do see that +it has a slot for a socket. +Unsurprisingly, that will be set up in the =*init*= handler. + +#+BEGIN_SRC scheme + (define (set-port-nonblocking! port) + (let ((flags (fcntl port F_GETFL))) + (fcntl port F_SETFL (logior O_NONBLOCK flags)))) + + (define (setup-socket) + ;; our socket + (define s + (socket PF_INET SOCK_STREAM 0)) + ;; reuse port even if busy + (setsockopt s SOL_SOCKET SO_REUSEADDR 1) + ;; connect to port 8889 on localhost + (bind s AF_INET INADDR_LOOPBACK 8889) + ;; make it nonblocking and start listening + (set-port-nonblocking! s) + (listen s 5) + s) + + (define (telcmd-init telcmd message) + (set! (telcmd-socket telcmd) (setup-socket)) + (display "Connect like: telnet localhost 8889\n") + (while (actor-alive? telcmd) + (let ((client-connection (accept (telcmd-socket telcmd)))) + (<- (actor-id telcmd) 'new-client client-connection)))) + + (define (telcmd-cleanup telcmd message) + (display "Closing socket!\n") + (when (telcmd-socket telcmd) + (close (telcmd-socket telcmd)))) +#+END_SRC + +That =setup-socket= code looks pretty hard to read! +But that's pretty standard code for setting up a socket. +One special thing is done though... the call to +=set-port-nonblocking!= sets flags on the socket port so that, +you guessed it, will be a nonblocking port. + +This is put to immediate use in the telcmd-init method. +This code looks suspiciously like it /should/ block... after +all, it just keeps looping forever. +But since 8sync is using Guile's suspendable ports code feature, +so every time this loop hits the =accept= call, if that call +/would have/ blocked, instead this whole procedure suspends +to the scheduler... automatically!... allowing other code to run. + +So, as soon as we do accept a connection, we send a message to +ourselves with the =new-client= action. +But wait! +Aren't actors only supposed to handle one message at a time? +If the telcmd-init loop just keeps on looping and looping, +when will the =new-client= message ever be handled? +8sync actors only receive one message at a time, but by default if an +actor's message handler suspends to the agenda for some reason (such +as to send a message or on handling I/O), that actor may continue to +accept other messages, but always in the same thread.[fn:queued-handler] + +We also see that we've established a =*cleanup*= handler. +This is run any time either the actor dies, either through self +destructing, because the hive completes its work, or because +a signal was sent to interrupt or terminate our program. +In our case, we politely close the socket when == dies. + +#+BEGIN_SRC scheme + (define (telcmd-new-client telcmd message client-connection) + (define client (car client-connection)) + (set-port-nonblocking! client) + (let loop () + (let ((line (read-line client))) + (cond ((eof-object? line) + (close client)) + (else + (telcmd-handle-line telcmd client + (string-trim-right line #\return)) + (when (actor-alive? telcmd) + (loop))))))) + + (define (telcmd-handle-line telcmd client line) + (match (string-split line #\space) + (("") #f) ; ignore empty lines + (("time" _ ...) + (display + (strftime "The time is: %c\n" (localtime (current-time))) + client)) + (("echo" rest ...) + (format client "~a\n" (string-join rest " "))) + ;; default + (_ (display "Sorry, I don't know that command.\n" client)))) +#+END_SRC + +Okay, we have a client, so we handle it! +And once again... we see this goes off on a loop of its own! +(Also once again, we have to do the =set-port-nonblocking!= song and +dance.) +This loop also automatically suspends when it would otherwise block... +as long as read-line has information to process, it'll keep going, but +if it would have blocked waiting for input, then it would suspend the +agenda.[fn:setvbuf] + +The actual method called whenever we have a "line" of input is pretty +straightforward... in fact it looks an awful lot like the IRC bot +handle-line procedure we used earlier. +No surprises there! + +Now let's run it: + +#+BEGIN_SRC scheme + (let* ((hive (make-hive)) + (telcmd (bootstrap-actor hive ))) + (run-hive hive '())) +#+END_SRC + +Open up another terminal... you can connect via telnet: + +#+BEGIN_SRC text +$ telnet localhost 8889 +Trying 127.0.0.1... +Connected to localhost. +Escape character is '^]'. +time +The time is: Thu Jan 5 03:20:17 2017 +echo this is an echo +this is an echo +shmmmmmmorp +Sorry, I don't know that command. +#+END_SRC + +Horray, it works! +Type =Ctrl+] Ctrl+d= to exit telnet. + +Not so bad! +There's more that could be optimized, but we'll consider that to be +advanced topics of discussion. + +So that's a pretty solid intro to how 8sync works! +Now that you've gone through this introduction, we hope you'll have fun +writing and hooking together your own actors. +Since actors are so modular, it's easy to have a program that has +multiple subystems working together. +You could build a worker queue system that displayed a web interface +and spat out notifications about when tasks finish to IRC, and making +all those actors talk to each other should be a piece of cake. +The sky's the limit! + +Happy hacking! + +[fn:setvbuf] + If there's a lot of data coming in and you don't want your I/O loop + to become too "greedy", take a look at =setvbuf=. + +[fn:queued-handler] + This is customizable: an actor can be set up to queue messages so + that absolutely no messages are handled until the actor completely + finishes handling one message. + Our loop couldn't look quite like this though! + * API reference