1 ;;; 8sync --- Asynchronous programming for Guile
2 ;;; Copyright (C) 2016 Christopher Allan Webber <cwebber@dustycloud.org>
4 ;;; This file is part of 8sync.
6 ;;; 8sync is free software: you can redistribute it and/or modify it
7 ;;; under the terms of the GNU Lesser General Public License as
8 ;;; published by the Free Software Foundation, either version 3 of the
9 ;;; License, or (at your option) any later version.
11 ;;; 8sync is distributed in the hope that it will be useful,
12 ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 ;;; GNU Lesser General Public License for more details.
16 ;;; You should have received a copy of the GNU Lesser General Public
17 ;;; License along with 8sync. If not, see <http://www.gnu.org/licenses/>.
19 (define-module (8sync actors)
20 #:use-module (oop goops)
21 #:use-module (srfi srfi-9)
22 #:use-module (srfi srfi-9 gnu)
23 #:use-module (ice-9 control)
24 #:use-module (ice-9 format)
25 #:use-module (ice-9 match)
26 #:use-module (ice-9 pretty-print)
27 #:use-module (8sync agenda)
28 #:use-module (8sync repl)
29 #:export (;; utilities... ought to go in their own module
31 big-random-number-string
32 simple-message-id-generator
40 ;;; Commenting out the <address> type for now;
41 ;;; it may be back when we have better serializers
44 address-actor-id address-hive-id
57 ;; There are more methods for the hive, but there's
58 ;; no reason for the outside world to look at them maybe?
60 hive-create-actor hive-create-actor*
62 create-actor create-actor*
67 message-to message-action message-from
68 message-id message-body message-in-reply-to
73 <- <-wait <-reply <-reply-wait
75 call-with-message msg-receive msg-val
80 serialize-message write-message
81 serialize-message-pretty pprint-message
82 read-message read-message-from-string))
86 (make-parameter (random-state-from-platform)))
88 ;; Same size as a uuid4 I think...
89 (define random-number-size (expt 2 128))
91 (define (big-random-number)
92 (random random-number-size (%random-state)))
94 ;; Would be great to get this base64 encoded instead.
95 (define (big-random-number-string)
96 ;; @@: This is slow. Using format here is wasteful.
97 (format #f "~x" (big-random-number)))
99 ;; @@: This is slow. A mere ~275k / second on my (old) machine.
100 ;; The main cost seems to be in number->string.
101 (define (simple-message-id-generator)
102 ;; Prepending this cookie makes message ids unique per hive
103 (let ((prefix (format #f "~x:" (big-random-number)))
106 (set! counter (1+ counter))
107 (string-append prefix (number->string counter)))))
115 ;; @@: We may want to add a deferred-reply to the below, similar to
116 ;; what we had in XUDD, for actors which do their own response
117 ;; queueing.... ie, that might receive messages but need to shelve
118 ;; them to be acted upon after something else is taken care of.
120 (define-record-type <message>
121 (make-message-intern id to from action
122 body in-reply-to wants-reply
128 (action message-action)
130 (in-reply-to message-in-reply-to)
131 (wants-reply message-wants-reply)
132 (replied message-replied set-message-replied!))
135 (define* (make-message id to from action body
136 #:key in-reply-to wants-reply
138 (make-message-intern id to from action body
139 in-reply-to wants-reply replied))
141 (define (message-auto-reply? message)
142 (eq? (message-action message) '*auto-reply*))
144 (define (message-needs-reply? message)
145 "See if this message needs a reply still"
146 (and (message-wants-reply message)
147 (not (message-replied message))))
150 (define (kwarg-list-to-alist args)
151 (let loop ((remaining args)
154 (((? keyword? key) val rest ...)
156 (cons (cons (keyword->symbol key) val)
159 (_ (throw 'invalid-kwarg-list
160 "Invalid keyword argument list"
164 ;;; See: https://web.archive.org/web/20081223021934/http://mumble.net/~jar/articles/oo-moon-weinreb.html
165 ;;; (also worth seeing: http://mumble.net/~jar/articles/oo.html )
167 (define (<- from-actor to-id action . message-body-args)
168 "Send a message from an actor to another actor"
169 (let* ((hive (actor-hive from-actor))
170 (message (make-message (hive-gen-message-id hive) to-id
171 (actor-id from-actor) action
173 (8sync (hive-process-message hive message))))
175 (define (<-wait from-actor to-id action . message-body-args)
176 "Send a message from an actor to another, but wait until we get a response"
177 (let* ((hive (actor-hive from-actor))
178 (abort-to (hive-prompt (actor-hive from-actor)))
179 (message (make-message (hive-gen-message-id hive) to-id
180 (actor-id from-actor) action
183 (abort-to-prompt abort-to from-actor message)))
185 ;; TODO: Intelligently ~propagate(ish) errors on -wait functions.
186 ;; We might have `send-message-wait-brazen' to allow callers to
187 ;; not have an exception thrown and instead just have a message with
188 ;; the appropriate '*error* message returned.
190 (define (<-reply from-actor original-message . message-body-args)
192 (set-message-replied! original-message #t)
193 (let* ((hive (actor-hive from-actor))
194 (new-message (make-message (hive-gen-message-id hive)
195 (message-from original-message)
196 (actor-id from-actor) '*reply*
198 #:in-reply-to (message-id original-message))))
199 (8sync (hive-process-message hive new-message))))
201 (define (<-auto-reply from-actor original-message)
202 "Auto-reply to a message. Internal use only!"
203 (set-message-replied! original-message #t)
204 (let* ((hive (actor-hive from-actor))
205 (new-message (make-message (hive-gen-message-id hive)
206 (message-from original-message)
207 (actor-id from-actor) '*auto-reply*
209 #:in-reply-to (message-id original-message))))
210 (8sync (hive-process-message hive new-message))))
212 (define (<-reply-wait from-actor original-message . message-body-args)
213 "Reply to a messsage, but wait until we get a response"
214 (set-message-replied! original-message #t)
215 (let* ((hive (actor-hive from-actor))
216 (abort-to (hive-prompt (actor-hive from-actor)))
217 (new-message (make-message (hive-gen-message-id hive)
218 (message-from original-message)
219 (actor-id from-actor) '*reply*
222 #:in-reply-to (message-id original-message))))
223 (abort-to-prompt abort-to from-actor new-message)))
227 ;;; Main actor implementation
228 ;;; =========================
230 (define (actor-inheritable-message-handler actor message)
231 (define action (message-action message))
232 (define (find-message-handler return)
233 (for-each (lambda (this-class)
235 (or (and (class-slot-definition this-class 'actions)
236 (class-slot-ref this-class 'actions))
238 (for-each (match-lambda
239 ((action-name . method)
240 (when (eq? action-name action)
243 (class-precedence-list (class-of actor)))
244 (throw 'action-not-found
245 "No appropriate action handler found for actor"
250 (call/ec find-message-handler))
251 (apply method actor message (message-body message)))
253 (define-class <actor> ()
255 (id #:init-keyword #:id
257 ;; The hive we're connected to.
258 ;; We need this to be able to send messages.
259 (hive #:init-keyword #:hive
260 #:accessor actor-hive)
261 ;; How we receive and process new messages
262 (message-handler #:init-value actor-inheritable-message-handler
263 ;; @@: There's no reason not to use #:class instead of
264 ;; #:each-subclass anywhere in this file, except for
265 ;; Guile bug #25211 (#:class is broken in Guile 2.2)
266 #:allocation #:each-subclass)
268 ;; This is the default, "simple" way to inherit and process messages.
269 (actions #:init-value '()
270 #:allocation #:each-subclass))
272 (define-method (actor-message-handler (actor <actor>))
273 (slot-ref actor 'message-handler))
275 ;;; So these are the nicer representations of addresses.
276 ;;; However, they don't serialize so easily with scheme read/write, so we're
277 ;;; using the simpler cons cell version below for now.
279 ;; (define-record-type <address>
280 ;; (make-address actor-id hive-id) ; @@: Do we want the trailing -id?
282 ;; (actor-id address-actor-id)
283 ;; (hive-id address-hive-id))
285 ;; (set-record-type-printer!
287 ;; (lambda (record port)
288 ;; (format port "<address: ~s@~s>"
289 ;; (address-actor-id record) (address-hive-id record))))
292 (define (make-address actor-id hive-id)
293 (cons actor-id hive-id))
295 (define (address-actor-id address)
298 (define (address-hive-id address)
301 (define (address->string address)
302 (string-append (address-actor-id address) "@"
303 (address-hive-id address)))
305 (define-method (actor-id-actor (actor <actor>))
306 "Get the actor id component of the actor-id"
307 (address-actor-id (actor-id actor)))
309 (define-method (actor-id-hive (actor <actor>))
310 "Get the hive id component of the actor-id"
311 (address-hive-id (actor-id actor)))
313 (define-method (actor-id-string (actor <actor>))
314 "Render the full actor id as a human-readable string"
315 (address->string (actor-id actor)))
317 (define %current-actor
325 (define-syntax-rule (build-actions (symbol method) ...)
326 "Construct an alist of (symbol . method), where the method is wrapped
327 with wrap-apply to facilitate live hacking and allow the method definition
328 to come after class definition."
331 (wrap-apply method)) ...))
333 (define-syntax-rule (define-simple-actor class action ...)
334 (define-class class (<actor>)
335 (actions #:init-value (build-actions action ...)
336 #:allocation #:each-subclass)))
341 ;;; Every actor has a hive. The hive is a kind of "meta-actor"
342 ;;; which routes all the rest of the actors in a system.
344 (define-generic hive-handle-failed-forward)
346 (define-class <hive> (<actor>)
347 (actor-registry #:init-thunk make-hash-table
348 #:getter hive-actor-registry)
349 (msg-id-generator #:init-thunk simple-message-id-generator
350 #:getter hive-msg-id-generator)
351 ;; Ambassadors are used (or will be) for inter-hive communication.
352 ;; These are special actors that know how to route messages to other hives.
353 (ambassadors #:init-thunk make-weak-key-hash-table
354 #:getter hive-ambassadors)
355 ;; Waiting coroutines
356 ;; This is a map from cons cell of message-id
357 ;; to a cons cell of (actor-id . coroutine)
358 ;; @@: Should we have a <waiting-coroutine> record type?
359 ;; @@: Should there be any way to clear out "old" coroutines?
360 (waiting-coroutines #:init-thunk make-hash-table
361 #:getter hive-waiting-coroutines)
363 ;; When actors send messages to each other they abort to this prompt
364 ;; to send the message, then carry on their way
365 (prompt #:init-thunk make-prompt-tag
366 #:getter hive-prompt)
367 (actions #:allocation #:each-subclass
370 ;; This is in the case of an ambassador failing to forward a
371 ;; message... it reports it back to the hive
372 (*failed-forward* hive-handle-failed-forward))))
374 (define-method (hive-handle-failed-forward (hive <hive>) message)
375 "Handle an ambassador failing to forward a message"
378 (define* (make-hive #:key hive-id)
379 (let ((hive (make <hive>
382 (big-random-number-string))))))
383 ;; Set the hive's actor reference to itself
384 (set! (actor-hive hive) hive)
387 (define-method (hive-id (hive <hive>))
388 (actor-id-hive hive))
390 (define-method (hive-gen-actor-id (hive <hive>) cookie)
391 (make-address (if cookie
392 (string-append cookie "-" (big-random-number-string))
393 (big-random-number-string))
396 (define-method (hive-gen-message-id (hive <hive>))
397 "Generate a message id using HIVE's message id generator"
398 ((hive-msg-id-generator hive)))
400 (define-method (hive-resolve-local-actor (hive <hive>) actor-address)
401 (hash-ref (hive-actor-registry hive) actor-address))
403 (define-method (hive-resolve-ambassador (hive <hive>) ambassador-address)
404 (hash-ref (hive-ambassadors hive) ambassador-address))
406 (define-method (make-forward-request (hive <hive>) (ambassador <actor>) message)
407 (make-message (hive-gen-message-id hive) (actor-id ambassador)
408 ;; If we make the hive not an actor, we could either switch this
409 ;; to #f or to the original actor...?
410 ;; Maybe some more thinking should be done on what should
411 ;; happen in case of failure to forward? Handling ambassador failures
412 ;; seems like the primary motivation for the hive remaining an actor.
415 `((original . ,message))))
417 (define-method (hive-reply-with-error (hive <hive>) original-message
418 error-key error-args)
419 ;; We only supply the error-args if the original sender is on the same hive
420 (define (orig-actor-on-same-hive?)
421 (equal? (hive-id hive)
422 (address-hive-id (message-from original-message))))
423 (set-message-replied! original-message #t)
424 (let* ((new-message-body
425 (if (orig-actor-on-same-hive?)
426 `(#:original-message ,original-message
427 #:error-key ,error-key
428 #:error-args ,error-args)
429 `(#:original-message ,original-message
430 #:error-key ,error-key)))
431 (new-message (make-message (hive-gen-message-id hive)
432 (message-from original-message)
433 (actor-id hive) '*error*
435 #:in-reply-to (message-id original-message))))
436 ;; We only return a thunk, rather than run 8sync here, because if
437 ;; we ran 8sync in the middle of a catch we'd end up with an
438 ;; unresumable continuation.
439 (lambda () (hive-process-message hive new-message))))
441 (define-method (hive-process-message (hive <hive>) message)
442 "Handle one message, or forward it via an ambassador"
443 (define (maybe-autoreply actor)
444 ;; Possibly autoreply
445 (if (message-needs-reply? message)
446 (<-auto-reply actor message)))
448 (define (resolve-actor-to)
449 "Get the actor the message was aimed at"
450 (let ((actor (hive-resolve-local-actor hive (message-to message))))
452 (throw 'actor-not-found
453 (format #f "Message ~a from ~a directed to nonexistant actor ~a"
455 (address->string (message-from message))
456 (address->string (message-to message)))
460 (define (call-catching-coroutine thunk)
461 (define queued-error-handling-thunk #f)
462 (define (call-catching-errors)
463 ;; TODO: maybe parameterize (or attach to hive) and use
464 ;; maybe-catch-all from agenda.scm
465 ;; @@: Why not just use with-throw-handler and let the catch
466 ;; happen at the agenda? That's what we used to do, but
467 ;; it ended up with a SIGABRT. See:
468 ;; http://lists.gnu.org/archive/html/bug-guile/2016-05/msg00003.html
471 ;; In the actor model, we don't totally crash on errors.
473 ;; If an error happens, we raise it
475 (if (message-needs-reply? message)
476 ;; If the message is waiting on a reply, let them know
477 ;; something went wrong.
478 ;; However, we have to do it outside of this catch
479 ;; routine, or we'll end up in an unrewindable continuation
481 (set! queued-error-handling-thunk
482 (hive-reply-with-error hive message key args)))
483 ;; print error message
484 (apply print-error-and-continue key args)))
485 ;; @@: This is a kludge. See above for why.
486 (if queued-error-handling-thunk
487 (8sync (queued-error-handling-thunk))))
488 (call-with-prompt (hive-prompt hive)
490 (lambda (kont actor message)
491 ;; Register the coroutine
492 (hash-set! (hive-waiting-coroutines hive)
494 (cons (actor-id actor) kont))
495 ;; Send off the message
496 (8sync (hive-process-message hive message)))))
498 (define (process-local-message)
499 (let ((actor (resolve-actor-to)))
500 (call-catching-coroutine
502 (define message-handler (actor-message-handler actor))
503 ;; @@: Should a more general error handling happen here?
504 (parameterize ((%current-actor actor))
506 (message-handler actor message)))
507 (maybe-autoreply actor)
508 ;; Returning result allows actors to possibly make a run-request
509 ;; at the end of handling a message.
510 ;; ... We do want that, right?
513 (define (resume-waiting-coroutine)
515 ((or (eq? (message-action message) '*reply*)
516 (eq? (message-action message) '*auto-reply*))
517 (call-catching-coroutine
519 (match (hash-remove! (hive-waiting-coroutines hive)
520 (message-in-reply-to message))
521 ((_ . (resume-actor-id . kont))
522 (if (not (equal? (message-to message)
524 (throw 'resuming-to-wrong-actor
525 "Attempted to resume a coroutine to the wrong actor!"
526 #:expected-actor-id (message-to message)
527 #:got-actor-id resume-actor-id
529 (let (;; @@: How should we resolve resuming coroutines to actors who are
531 (actor (resolve-actor-to))
532 (result (kont message)))
533 (maybe-autoreply actor)
535 (#f (throw 'no-waiting-coroutine
536 "message in-reply-to tries to resume nonexistent coroutine"
538 ;; Yikes, we must have gotten an error or something back
540 ;; @@: Not what we want in the long run?
541 ;; What we'd *prefer* to do is to resume this message
542 ;; and throw an error inside the message handler
543 ;; (say, from send-mesage-wait), but that causes a SIGABRT (??!!)
544 (hash-remove! (hive-waiting-coroutines hive)
545 (message-in-reply-to message))
547 (if (eq? (message-action message) '*reply*)
548 "Won't resume coroutine; got an *error* as a reply"
549 "Won't resume coroutine because action is not *reply*")))
550 (throw 'hive-unresumable-coroutine
552 #:message message)))))
554 (define (process-remote-message)
555 ;; Find the ambassador
556 (let* ((remote-hive-id (hive-id (message-to message)))
557 (ambassador (hive-resolve-ambassador remote-hive-id))
558 (message-handler (actor-message-handler ambassador))
559 (forward-request (make-forward-request hive ambassador message)))
560 (message-handler ambassador forward-request)))
562 (let ((to (message-to message)))
563 ;; This seems to be an easy mistake to make, so check that addressing
566 (throw 'missing-addressee
567 "`to' field is missing on message"
569 (if (hive-actor-local? hive to)
570 (if (message-in-reply-to message)
571 (resume-waiting-coroutine)
572 (process-local-message))
573 (process-remote-message))))
575 (define-method (hive-actor-local? (hive <hive>) address)
576 (equal? (hive-id hive) (address-hive-id address)))
578 (define-method (hive-register-actor! (hive <hive>) (actor <actor>))
579 (hash-set! (hive-actor-registry hive) (actor-id actor) actor))
581 (define-method (%hive-create-actor (hive <hive>) actor-class
583 "Actual method called by hive-create-actor.
585 Since this is a define-method it can't accept fancy define* arguments,
586 so this gets called from the nicer hive-create-actor interface. See
587 that method for documentation."
588 (let* ((actor-id (hive-gen-actor-id hive id-cookie))
589 (actor (apply make actor-class
593 (hive-register-actor! hive actor)
594 ;; return the actor id
597 (define* (hive-create-actor hive actor-class #:rest init)
598 (%hive-create-actor hive actor-class
601 (define* (hive-create-actor* hive actor-class id-cookie #:rest init)
602 (%hive-create-actor hive actor-class
605 (define (call-with-message message proc)
606 "Applies message body arguments into procedure, with message as first
607 argument. Similar to call-with-values in concept."
608 (apply proc message (message-body message)))
610 ;; (msg-receive (<- bar baz)
614 ;; Emacs: (put 'msg-receive 'scheme-indent-function 2)
616 ;; @@: Or receive-msg or receieve-message or??
617 (define-syntax-rule (msg-receive arglist message body ...)
618 "Call body with arglist (which can accept arguments like lambda*)
619 applied from the message-body of message."
620 (call-with-message message
624 (define (msg-val message)
625 "Retrieve the first value from the message-body of message.
626 Like single value return from a procedure call. Probably the most
627 common case when waiting on a reply from some action invocation."
628 (call-with-message message
629 (lambda (_ val) val)))
632 ;;; Various API methods for actors to interact with the system
633 ;;; ==========================================================
635 ;; TODO: move send-message and friends here...?
637 (define* (create-actor from-actor actor-class #:rest init)
638 "Create an instance of actor-class. Return the new actor's id.
640 This is the method actors should call directly (unless they want
641 to supply an id-cookie, in which case they should use
643 (%hive-create-actor (actor-hive from-actor) actor-class
647 (define* (create-actor* from-actor actor-class id-cookie #:rest init)
648 "Create an instance of actor-class. Return the new actor's id.
650 Like create-actor, but permits supplying an id-cookie."
651 (%hive-create-actor (actor-hive from-actor) actor-class
655 (define (self-destruct actor)
656 "Remove an actor from the hive."
657 (hash-remove! (hive-actor-registry (actor-hive actor))
662 ;;; 8sync bootstrap utilities
663 ;;; =========================
665 (define* (ez-run-hive hive initial-tasks #:key repl-server)
666 "Start up an agenda and run HIVE in it with INITIAL-TASKS.
668 Should we start up a cooperative REPL for live hacking? REPL-SERVER
669 wants to know! You can pass it #t or #f, or if you want to specify a port,
671 (let* ((queue (list->q initial-tasks))
672 (agenda (make-agenda #:pre-unwind-handler print-error-and-continue
675 ;; If repl-server is an integer, we'll use that as the port
676 ((integer? repl-server)
677 (spawn-and-queue-repl-server! agenda repl-server))
679 (spawn-and-queue-repl-server! agenda)))
680 (start-agenda agenda)))
682 (define (bootstrap-message hive to-id action . message-body-args)
684 (apply <- hive to-id action message-body-args)))
688 ;;; Basic readers / writers
689 ;;; =======================
691 (define (serialize-message message)
692 "Serialize a message for read/write"
696 (message-from message)
697 (message-action message)
698 (message-body message)
699 (message-in-reply-to message)
700 (message-wants-reply message)
701 (message-replied message)))
703 (define* (write-message message #:optional (port (current-output-port)))
704 "Write out a message to a port for easy reading later.
706 Note that if a sub-value can't be easily written to something
707 Guile's `read' procedure knows how to read, this doesn't do anything
708 to improve that. You'll need a better serializer for that.."
709 (write (serialize-message message) port))
711 (define (serialize-message-pretty message)
712 "Serialize a message in a way that's easy for humans to read."
714 (id ,(message-id message))
715 (to ,(message-to message))
716 (from ,(message-from message))
717 (action ,(message-action message))
718 (body ,(message-body message))
719 (in-reply-to ,(message-in-reply-to message))
720 (wants-reply ,(message-wants-reply message))
721 (replied ,(message-replied message))))
723 (define (pprint-message message)
724 "Pretty print a message."
725 (pretty-print (serialize-message-pretty message)))
727 (define* (read-message #:optional (port (current-input-port)))
728 "Read a message serialized via serialize-message from PORT"
730 ((id to from action body in-reply-to wants-reply replied)
732 id to from action body
733 in-reply-to wants-reply replied))
735 (throw 'message-read-bad-structure
736 "Could not read message from structure"
739 (define (read-message-from-string message-str)
740 "Read message from MESSAGE-STR"
741 (with-input-from-string message-str
743 (read-message (current-input-port)))))