-# Permission is granted to copy, distribute and/or modify this document
-# under the terms of the GNU Free Documentation License, Version 1.3
-# or any later version published by the Free Software Foundation;
-# with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
-# A copy of the license is included in the section entitled ``GNU
-# Free Documentation License''.
-#
-# A copy of the license is also available from the Free Software
-# Foundation Web site at http://www.gnu.org/licenses/fdl.html
-#
-# Alternately, this document is also available under the Lesser General
-# Public License, version 3 or later, as published by the Free Software
-# Foundation.
-#
-# A copy of the license is also available from the Free Software
-# Foundation Web site at http://www.gnu.org/licenses/lgpl.html
-
-* Preface
-
-Welcome to 8sync's documentation!
-8sync is an asynchronous programming environment for GNU Guile.
-(Get it? 8sync? Async??? Quiet your groans, it's a great name!)
-
-8sync has some nice properties:
-
- - 8sync uses the actor model as its fundamental concurrency
- synchronization mechanism.
- Since the actor model is a "shared nothing" asynchronous
- environment, you don't need to worry about deadlocks or other
- tricky problems common to other asynchronous models.
- Actors are modular units of code and state which communicate
- by sending messages to each other.
- - If you've done enough asynchronous programming, you're probably
- familiar with the dreaded term "callback hell".
- Getting around callback hell usually involves a tradeoff of other,
- still rather difficult to wrap your brain around programming
- patterns.
- 8sync uses some clever tricks involving "delimited continuations"
- under the hood to make the code you write look familiar and
- straightforward.
- When you need to send a request to another actor and get some
- information back from it without blocking, there's no need
- to write a separate procedure... 8sync's scheduler will suspend
- your procedure and wake it back up when a response is ready.
- - Even nonblocking I/O code is straightforward to write.
- Thanks to the "suspendable ports" code introduced in Guile 2.2,
- writing asynchronous, nonblocking networked code looks mostly
- like writing the same synchronous code.
- 8sync's scheduler handles suspending and resuming networked
- code that would otherwise block.
- - 8sync aims to be "batteries included".
- Useful subsystems for IRC bots, HTTP servers, and so on are
- included out of the box.
- - 8sync prioritizes live hacking.
- If using an editor like Emacs with a nice mode like Geiser,
- an 8sync-using developer can change and fine-tune the behavior
- of code /while it runs/.
- This makes both debugging and development much more natural,
- allowing the right designs to evolve under your fingertips.
- A productive hacker is a happy hacker, after all!
-
-In the future, 8sync will also provide the ability to spawn and
-communicate with actors on different threads, processes, and machines,
-with most code running the same as if actors were running in the same
-execution environment.
-
-But as a caution, 8sync is still very young.
-The API is stabilizing, but not yet stable, and it is not yet well
-"battle-tested".
-Hacker beware!
-But, consider this as much an opportunity as a warning.
-8sync is in a state where there is much room for feedback and
-contributions.
-Your help wanted!
-
-And now, into the wild, beautiful frontier.
-Onward!
-
-* 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.[fn:irc-hacking]
-We ourselves are going to explore chat bots as a basis for getting our
-feet wet in 8sync.
-
-First of all, we're going to need to import some modules. Put this at
-the top of your file:
-
-#+BEGIN_SRC scheme
- (use-modules (8sync) ; 8sync's agenda and actors
- (8sync systems irc) ; the irc bot subsystem
- (oop goops) ; 8sync's actors use GOOPS
- (ice-9 format) ; basic string formatting
- (ice-9 match)) ; pattern matching
-#+END_SRC
-
-Now we need to add our bot. Initially, it won't do much.
-
-#+BEGIN_SRC scheme
- (define-class <my-irc-bot> (<irc-bot>))
-
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- (if emote?
- (format #t "~a emoted ~s in channel ~a\n"
- speaker line channel)
- (format #t "~a said ~s in channel ~a\n"
- speaker line channel)))
-#+END_SRC
-
-We've just defined our own IRC bot!
-This is an 8sync actor.
-(8sync uses GOOPS to define actors.)
-We extended the handle-line generic method, so this is the code that
-will be called whenever the IRC bot "hears" anything.
-This method is itself an action handler, hence the second argument
-for =message=, which we can ignore for now.
-Pleasantly, the message's argument body is passed in as the rest of
-the arguments.
-
-For now the code is pretty basic: it just outputs whatever it "hears"
-from a user in a channel to the current output port.
-Pretty boring!
-But it should help us make sure we have things working when we kick
-things off.
-
-Speaking of, even though we've defined our actor, it's not running
-yet. Time to fix that!
-
-#+BEGIN_SRC scheme
-(define* (run-bot #:key (username "examplebot")
- (server "irc.freenode.net")
- (channels '("##botchat")))
- (define hive (make-hive))
- (define irc-bot
- (bootstrap-actor hive <my-irc-bot>
- #:username username
- #:server server
- #:channels channels))
- (run-hive hive '()))
-#+END_SRC
-
-Actors are connected to something called a "hive", which is a
-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
-argument, and the rest are initialization arguments to the
-actor.
-=bootstrap-actor= passes back not the actor itself (we don't
-get access to that usually) but the *id* of the actor.
-(More on this later.)
-Finally we run the hive with run-hive and pass it a list of
-"bootstrapped" messages.
-Normally actors send messages to each other (and sometimes themselves),
-but we need to send a message or messages to start things or else
-nothing is going to happen.
-
-We can run it like:
-
-#+BEGIN_SRC scheme
-(run-bot #:username "some-bot-name") ; be creative!
-#+END_SRC
-
-Assuming all the tubes on the internet are properly connected, you
-should be able to join the "##botchat" channel on irc.freenode.net and
-see your bot join as well.
-Now, as you probably guessed, you can't really /do/ much yet.
-If you talk to the bot, it'll send messages to the terminal informing
-you as such, but it's hardly a chat bot if it's not chatting yet.
-
-So let's do the most boring (and annoying) thing possible.
-Let's get it to echo whatever we say back to us.
-Change handle-line to this:
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- (<- (actor-id irc-bot) 'send-line channel
- (format #f "Bawwwwk! ~a says: ~a" speaker line)))
-#+END_SRC
-
-This will do exactly what it looks like: repeat back whatever anyone
-says like an obnoxious parrot.
-Give it a try, but don't keep it running for too long... this
-bot is so annoying it's likely to get banned from whatever channel
-you put it in.
-
-This method handler does have the advantage of being simple though.
-It introduces a new concept simply... sending a message!
-Whenever you see "<-", you can think of that as saying "send this
-message".
-The arguments to "<-" are as follows: the actor sending the message,
-the id of the actor the message is being sent to, the "action" we
-want to invoke (a symbol), and the rest are arguments to the
-"action handler" which is in this case send-line (with itself takes
-two arguments: the channel our bot should send a message to, and
-the line we want it to spit out to the channel).[fn:send-message-provenance]
-
-Normally in the actor model, we don't have direct references to
-an actor, only an identifier.
-This is for two reasons: to quasi-enforce the "shared nothing"
-environment (actors absolutely control their own resources, and
-"all you can do is send a message" to request that they modify
-them) and because... well, you don't even know where that actor is!
-Actors can be anything, and anywhere.
-It's possible in 8sync to have an actor on a remote hive, which means
-the actor could be on a remote process or even remote machine, and
-in most cases message passing will look exactly the same.
-(There are some exceptions; it's possible for two actors on the same
-hive to "hand off" some special types of data that can't be serialized
-across processes or the network, eg a socket or a closure, perhaps even
-one with mutable state.
-This must be done with care, and the actors should be careful both
-to ensure that they are both local and that the actor handing things
-off no longer accesses that value to preserve the actor model.
-But this is an advanced topic, and we are getting ahead of ourselves.)
-We have to supply the id of the receiving actor, and usually we'd have
-only the identifier.
-But since in this case, since the actor we're sending this to is
-ourselves, we have to pass in our identifier, since the Hive won't
-deliver to anything other than an address.
-
-Astute readers may observe, since this is a case where we are just
-referencing our own object, couldn't we just call "sending a line"
-as a method of our own object without all the message passing?
-Indeed, we do have such a method, so we /could/ rewrite handle-line
-like so:
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- (irc-bot-send-line irc-bot channel
- (format #f "Bawwwwk! ~a says: ~a" speaker line)))
-#+END_SRC
-
-... but we want to get you comfortable and familiar with message
-passing, and we'll be making use of this same message passing shortly
-so that /other/ actors may participate in communicating with IRC
-through our IRC bot.
-
-Anyway, our current message handler is simply too annoying.
-What we would really like to do is have our bot respond to individual
-"commands" like this:
-
-#+BEGIN_SRC text
- <foo-user> examplebot: hi!
- <examplebot> Oh hi foo-user!
- <foo-user> examplebot: botsnack
- <examplebot> Yippie! *does a dance!*
- <foo-user> examplebot: echo I'm a very silly bot
- <examplebot> I'm a very silly bot
-#+END_SRC
-
-Whee, that looks like fun!
-To implement it, we're going to pull out Guile's pattern matcher.
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- (define my-name (irc-bot-username irc-bot))
- (define (looks-like-me? str)
- (or (equal? str my-name)
- (equal? str (string-concatenate (list my-name ":")))))
- (match (string-split line #\space)
- (((? looks-like-me? _) action action-args ...)
- (match action
- ;; The classic botsnack!
- ("botsnack"
- (<- (actor-id irc-bot) 'send-line channel
- "Yippie! *does a dance!*"))
- ;; Return greeting
- ((or "hello" "hello!" "hello." "greetings" "greetings." "greetings!"
- "hei" "hei." "hei!" "hi" "hi!")
- (<- (actor-id irc-bot) 'send-line channel
- (format #f "Oh hi ~a!" speaker)))
- ("echo"
- (<- (actor-id irc-bot) 'send-line channel
- (string-join action-args " ")))
-
- ;; ---> Add yours here <---
-
- ;; Default
- (_
- (<- (actor-id irc-bot) 'send-line channel
- "*stupid puppy look*"))))))
-#+END_SRC
-
-Parsing the pattern matcher syntax is left as an exercise for the
-reader.
-
-If you're getting the sense that we could make this a bit less wordy,
-you're right:
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- (define my-name (irc-bot-username irc-bot))
- (define (looks-like-me? str)
- (or (equal? str my-name)
- (equal? str (string-concatenate (list my-name ":")))))
- (define (respond respond-line)
- (<- (actor-id irc-bot) 'send-line channel
- respond-line))
- (match (string-split line #\space)
- (((? looks-like-me? _) action action-args ...)
- (match action
- ;; The classic botsnack!
- ("botsnack"
- (respond "Yippie! *does a dance!*"))
- ;; Return greeting
- ((or "hello" "hello!" "hello." "greetings" "greetings." "greetings!"
- "hei" "hei." "hei!" "hi" "hi." "hi!")
- (respond (format #f "Oh hi ~a!" speaker)))
- ("echo"
- (respond (string-join action-args " ")))
-
- ;; ---> Add yours here <---
-
- ;; Default
- (_
- (respond "*stupid puppy look*"))))))
-#+END_SRC
-
-Okay, that looks pretty good!
-Now we have enough information to build an IRC bot that can do a lot
-of things.
-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 a few decades ago.
-
-[fn:send-message-provenance]
- 8sync's name for sending a message, "<-", comes from older,
- early lisp object oriented systems which were, as it turned out,
- inspired by the actor model!
- Eventually message passing was dropped in favor of something called
- "generic functions" or "generic methods"
- (you may observe we made use of such a thing in extending
- handle-line).
- Many lispers believe that there is no need for message passing
- with generic methods and some advanced functional techniques,
- but in a concurrent environment message passing becomes useful
- again, especially when the communicating objects / actors are not
- in the same address space.
-
-** Writing our own actors
-
-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 <sleeper> (<actor>)
- (actions #:allocation #:each-subclass
- #:init-value (build-actions
- (*init* sleeper-loop))))
-
- (define (sleeper-loop actor message)
- (while (actor-alive? actor)
- (display "Zzzzzzzz....\n")
- ;; Sleep for one second
- (8sleep (sleeper-sleep-secs actor))))
-
- (let* ((hive (make-hive))
- (sleeper (bootstrap-actor hive <sleeper>)))
- (run-hive hive '()))
-#+END_SRC
-
-We see some particular things in this example.
-One thing is that our =<sleeper>= 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=.[fn:class-bug]
-
-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.
-
-Our while loop also checks "actor-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.[fn:actor-alive-deprecated-soon]
-(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.)
-
-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 <sleeper> (<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 <sleeper> (<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-actor <manager> (<actor>)
- ((assign-task manager-assign-task))
- (direct-report #:init-keyword #:direct-report
- #:getter manager-direct-report))
-
- (define (manager-assign-task manager message difficulty)
- "Delegate a task to our direct report"
- (display "manager> Work on this task for me!\n")
- (<- (manager-direct-report manager)
- 'work-on-this difficulty))
-#+END_SRC
-
-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-actor <worker> (<actor>)
- ((work-on-this worker-work-on-this))
- (task-left #:init-keyword #:task-left
- #:accessor worker-task-left))
-
- (define (worker-work-on-this worker message difficulty)
- "Work on one task until done."
- (set! (worker-task-left worker) difficulty)
- (display "worker> Whatever you say, boss!\n")
- (while (and (actor-alive? worker)
- (> (worker-task-left worker) 0))
- (display "worker> *huff puff*\n")
- (set! (worker-task-left worker)
- (- (worker-task-left worker) 1))
- (8sleep (/ 1 3))))
-#+END_SRC
-
-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.
-
-#+BEGIN_SRC scheme
- (let* ((hive (make-hive))
- (worker (bootstrap-actor hive <worker>))
- (manager (bootstrap-actor hive <manager>
- #:direct-report worker)))
- (run-hive hive (list (bootstrap-message hive manager 'assign-task 5))))
-#+END_SRC
-
-Unlike the =<sleeper>=, our =<manager>= 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!
-worker> *huff puff*
-worker> *huff puff*
-worker> *huff puff*
-worker> *huff puff*
-worker> *huff puff*
-#+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.
-
-#+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-direct-report manager)
- 'work-on-this difficulty)
-
- ;; Wait a moment, then call the micromanagement loop
- (8sleep (/ 1 2))
- (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 ((worker-is-done
- (mbody-val (<-wait (manager-direct-report manager)
- 'done-yet?))))
- (if worker-is-done
- (begin (display "manager> Oh! I guess you can go home then.\n")
- (<- (manager-direct-report manager) 'go-home))
- (begin (display "manager> Harumph!\n")
- (8sleep (/ 1 2))
- (when (actor-alive? manager)
- (manager-micromanage-loop manager))))))
-#+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 mbody-val.
-(It's possible for a remote actor to return multiple values, in which
-case we'd want to use mbody-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-actor <worker> (<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))
-
- ;;; New procedures:
- (define (worker-done-yet? worker message)
- "Reply with whether or not we're done yet."
- (let ((am-i-done? (= (worker-task-left worker) 0)))
- (if am-i-done?
- (display "worker> Yes, I finished up!\n")
- (display "worker> No... I'm still working on it...\n"))
- (<-reply message am-i-done?)))
-
- (define (worker-go-home worker message)
- "It's off of work for us!"
- (display "worker> Whew! Free at last.\n")
- (self-destruct worker))
-#+END_SRC
-
-(As you've probably guessed, you wouldn't normally call =display=
-everywhere as we are in this program... that's just to make the
-examples more illustrative.)
-
-"<-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!
-
-Running it is the same as before:
-
-#+BEGIN_SRC scheme
- (let* ((hive (make-hive))
- (worker (bootstrap-actor hive <worker>))
- (manager (bootstrap-actor hive <manager>
- #:direct-report worker)))
- (run-hive hive (list (bootstrap-message hive manager 'assign-task 5))))
-#+END_SRC
-
-But the output is a bit different:
-
-#+BEGIN_SRC scheme
-manager> Work on this task for me!
-worker> Whatever you say, boss!
-worker> *huff puff*
-worker> *huff puff*
-manager> Are you done yet???
-worker> No... I'm still working on it...
-manager> Harumph!
-worker> *huff puff*
-manager> Are you done yet???
-worker> *huff puff*
-worker> No... I'm still working on it...
-manager> Harumph!
-worker> *huff puff*
-manager> Are you done yet???
-worker> Yes, I finished up!
-manager> Oh! I guess you can go home then.
-worker> Whew! Free at last.
-#+END_SRC
-
-[fn:class-bug]
- #: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.
-
-[fn:actor-alive-deprecated-soon]
- Or rather, for now you should call =actor-alive?= if your code
- is looping like this.
- In the future, after an actor dies, its coroutines will
- automatically be "canceled".
-
-** 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 <telcmd> (<actor>)
- ((*init* telcmd-init)
- (*cleanup* telcmd-cleanup)
- (new-client telcmd-new-client)
- (handle-line telcmd-handle-line))
- (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 =<telcmd>= 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
- (<- (actor-id telcmd) 'handle-line
- client (string-trim-right line #\return))
- (when (actor-alive? telcmd)
- (loop)))))))
-
- (define (telcmd-handle-line telcmd message 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![fn:why-send-a-message-to-handle-line]
-
-Now let's run it:
-
-#+BEGIN_SRC scheme
- (let* ((hive (make-hive))
- (telcmd (bootstrap-actor hive <telcmd>)))
- (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!
-
-[fn:why-send-a-message-to-handle-line]
- Well, there may be one surprise to a careful observer.
- Why are we sending a message to ourselves?
- Couldn't we have just dropped the argument of "message" to
- telcmd-handle-line and just called it like any other procedure?
- Indeed, we /could/ do that, but sending a message to ourself has
- an added advantage: if we accidentally "break" the
- telcmd-handle-line procedure in some way (say we add a fun new
- command we're playing with it), raising an exception won't break
- and disconnect the client's main loop, it'll just break the
- message handler for that one line, and our telcmd will happily
- chug along accepting another command from the user while we try
- to figure out what happened to the last one.
-
-** An intermission on live hacking
-
-This section is optional, but highly recommended.
-It requires that you're a user of GNU Emacs.
-If you aren't, don't worry... you can forge ahead and come back in case
-you ever do become an Emacs user.
-(If you're more familiar with Vi/Vim style editing, I hear good things
-about Spacemacs...)
-
-Remember all the way back when we were working on the IRC bot?
-So you may have noticed while updating that section that the
-start/stop cycle of hacking isn't really ideal.
-You might either edit a file in your editor, then run it, or
-type the whole program into the REPL, but then you'll have to spend
-extra time copying it to a file.
-Wouldn't it be nice if it were possible to both write code in a
-file and try it as you go?
-And wouldn't it be even better if you could live edit a program
-while it's running?
-
-Luckily, there's a great Emacs mode called Geiser which makes
-editing and hacking and experimenting all happen in harmony.
-And even better, 8sync is optimized for this experience.
-8sync provides easy drop-in "cooperative REPL" support, and
-most code can be simply redefined on the fly in 8sync through Geiser
-and actors will immediately update their behavior, so you can test
-and tweak things as you go.
-
-Okay, enough talking. Let's add it!
-Redefine run-bot like so:
-
-#+BEGIN_SRC scheme
- (define* (run-bot #:key (username "examplebot")
- (server "irc.freenode.net")
- (channels '("##botchat"))
- (repl-path "/tmp/8sync-repl"))
- (define hive (make-hive))
- (define irc-bot
- (bootstrap-actor hive <my-irc-bot>
- #:username username
- #:server server
- #:channels channels))
- (define repl-manager
- (bootstrap-actor hive <repl-manager>
- #:path repl-path))
-
- (run-hive hive '()))
-#+END_SRC
-
-If we put a call to run-bot at the bottom of our file we can call it,
-and the repl-manager will start something we can connect to automatically.
-Horray!
-Now when we run this it'll start up a REPL with a unix domain socket at
-the repl-path.
-We can connect to it in emacs like so:
-
-: M-x geiser-connect-local <RET> guile <RET> /tmp/8sync-repl <RET>
-
-Okay, so what does this get us?
-Well, we can now live edit our program.
-Let's change how our bot behaves a bit.
-Let's change handle-line and tweak how the bot responds to a botsnack.
-Change this part:
-
-#+BEGIN_SRC scheme
- ;; From this:
- ("botsnack"
- (respond "Yippie! *does a dance!*"))
-
- ;; To this:
- ("botsnack"
- (respond "Yippie! *catches botsnack in midair!*"))
-#+END_SRC
-
-Okay, now let's evaluate the change of the definition.
-You can hit "C-M-x" anywhere in the definition to re-evaluate.
-(You can also position your cursor at the end of the definition and press
-"C-x C-e", but I've come to like "C-M-x" better because I can evaluate as soon
-as I'm done writing.)
-Now, on IRC, ask your bot for a botsnack.
-The bot should give the new message... with no need to stop and start the
-program!
-
-Let's fix a bug live.
-Our current program works great if you talk to your bot in the same
-IRC channel, but what if you try to talk to them over private message?
-
-#+BEGIN_SRC text
-IRC> /query examplebot
-<foo-user> examplebot: hi!
-#+END_SRC
-
-Hm, we aren't seeing any response on IRC!
-Huh? What's going on?
-It's time to do some debugging.
-There are plenty of debugging tools in Guile, but sometimes the simplest
-is the nicest, and the simplest debugging route around is good old
-fashioned print debugging.
-
-It turns out Guile has an under-advertised feature which makes print
-debugging really easy called "pk", pronounced "peek".
-What pk accepts a list of arguments, prints out the whole thing,
-but returns the last argument.
-This makes wrapping bits of our code pretty easy to see what's
-going on.
-So let's peek into our program with pk.
-Edit the respond section to see what channel it's really sending
-things to:
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- ;; [... snip ...]
- (define (respond respond-line)
- (<- (actor-id irc-bot) 'send-line (pk 'channel channel)
- respond-line))
- ;; [... snip ...]
- )
-#+END_SRC
-
-Re-evaluate.
-Now let's ping our bot in both the channel and over PM.
-
-#+BEGIN_SRC text
-;;; (channel "##botchat")
-
-;;; (channel "sinkbot")
-#+END_SRC
-
-Oh okay, this makes sense.
-When we're talking in a normal multi-user channel, the channel we see
-the message coming from is the same one we send to.
-But over PM, the channel is a username, and in this case the username
-we're sending our line of text to is ourselves.
-That isn't what we want.
-Let's edit our code so that if we see that the channel we're sending
-to looks like our own username that we respond back to the sender.
-(We can remove the pk now that we know what's going on.)
-
-#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) message
- speaker channel line emote?)
- ;; [... snip ...]
- (define (respond respond-line)
- (<- (actor-id irc-bot) 'send-line
- (if (looks-like-me? channel)
- speaker ; PM session
- channel) ; normal IRC channel
- respond-line))
- ;; [... snip ...]
- )
-#+END_SRC
-
-Re-evaluate and test.
-
-#+BEGIN_SRC text
-IRC> /query examplebot
-<foo-user> examplebot: hi!
-<examplebot> Oh hi foo-user!
-#+END_SRC
-
-Horray!
-
-
-* API reference
-
-* Systems reference
-** IRC
-** Web / HTTP
-** COMMENT Websockets
-
-* Addendum
-** Recommended .emacs additions
-
-In order for =mbody-receive= to indent properly, put this in your
-.emacs:
-
-#+BEGIN_SRC emacs-lisp
-(put 'mbody-receive 'scheme-indent-function 2)
-#+END_SRC
-
-** 8sync and Fibers
-
-One other major library for asynchronous communication in Guile-land
-is [[https://github.com/wingo/fibers/][Fibers]].
-There's a lot of overlap:
-
- - Both use Guile's suspendable-ports facility
- - Both communicate between asynchronous processes using message passing;
- you don't have to squint hard to see the relationship between Fibers'
- channels and 8sync's actor inboxes.
-
-However, there are clearly differences too.
-There's a one to one relationship between 8sync actors and an actor inbox,
-whereas each Fibers fiber may read from multiple channels, for example.
-
-Luckily, it turns out there's a clear relationship, based on real,
-actual theory!
-8sync is based on the [[https://en.wikipedia.org/wiki/Actor_model][actor model]] whereas fibers follows
-[[http://usingcsp.com/][Communicating Sequential Processes (CSP)]], which is a form of
-[[https://en.wikipedia.org/wiki/Process_calculus][process calculi]].
-And it turns out, the
-[[https://en.wikipedia.org/wiki/Actor_model_and_process_calculi][relationship between the actor model and process calculi]] is well documented,
-and even more precisely, the
-[[https://en.wikipedia.org/wiki/Communicating_sequential_processes#Comparison_with_the_Actor_Model][relationship between CSP and the actor model]] is well understood too.
-
-So, 8sync and Fibers do take somewhat different approaches, but both
-have a solid theoretical backing... and their theories are well
-understood in terms of each other.
-Good news for theory nerds!
-
-(Since the actors and CSP are [[https://en.wikipedia.org/wiki/Dual_%28mathematics%29][dual]], maybe eventually 8sync will be
-implemented on top of Fibers... that remains to be seen!)
-
projects / 8sync.git / commitdiff