1 ;;; 8sync --- Asynchronous programming for Guile
2 ;;; Copyright © 2016, 2017 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 (ice-9 control)
23 #:use-module (ice-9 format)
24 #:use-module (ice-9 match)
25 #:use-module (ice-9 atomic)
26 #:use-module (ice-9 pretty-print)
27 #:use-module (ice-9 receive)
29 #:use-module (fibers channels)
30 #:use-module (fibers conditions)
31 #:use-module (fibers operations)
32 #:use-module (8sync agenda)
33 #:use-module (8sync inbox)
34 #:use-module (8sync rmeta-slot)
35 #:export (;; utilities... ought to go in their own module
37 big-random-number-string
43 ;;; Commenting out the <address> type for now;
44 ;;; it may be back when we have better serializers
47 address-actor-id address-hive-id
49 actor-init! actor-cleanup!
64 ;; ;; There are more methods for the hive, but there's
65 ;; ;; no reason for the outside world to look at them maybe?
67 bootstrap-actor bootstrap-actor*
69 create-actor create-actor*
74 message-to message-action message-from
75 message-id message-body message-in-reply-to
85 (set! *random-state* (random-state-from-platform))
87 ;; Same size as a uuid4 I think...
88 (define random-number-size (expt 2 128))
90 (define (big-random-number)
91 (random random-number-size))
93 ;; Would be great to get this base64 encoded instead.
94 (define (big-random-number-string)
95 ;; @@: This is slow. Using format here is wasteful.
96 (format #f "~x" (big-random-number)))
98 ;; @@: This is slow-ish. A mere ~275k / second on my (old) machine.
99 ;; The main cost seems to be in number->string.
100 (define (simple-message-id-generator)
101 ;; Prepending this cookie makes message ids unique per hive
102 (let ((prefix (format #f "~x:" (big-random-number)))
105 (set! counter (1+ counter))
106 (string-append prefix (number->string counter)))))
113 (define-record-type <message>
114 (make-message-intern id to from action
115 body in-reply-to wants-reply)
117 ;; @@: message-ids are removed. They could be re-enabled
118 ;; if we had thread-safe promises...
119 (id message-id) ; id of this message
120 (to message-to) ; actor id this is going to
121 (from message-from) ; actor id of sender
122 (action message-action) ; action (a symbol) to be handled
123 (body message-body) ; argument list "body" of message
124 (in-reply-to message-in-reply-to) ; message id this is in reply to, if any
125 (wants-reply message-wants-reply)) ; whether caller is waiting for reply
128 (define* (make-message id to from action body
129 #:key in-reply-to wants-reply)
130 (make-message-intern id to from action body
131 in-reply-to wants-reply))
133 (define (kwarg-list-to-alist args)
134 (let loop ((remaining args)
137 (((? keyword? key) val rest ...)
139 (cons (cons (keyword->symbol key) val)
142 (_ (throw 'invalid-kwarg-list
143 "Invalid keyword argument list"
147 ;;; See: https://web.archive.org/web/20081223021934/http://mumble.net/~jar/articles/oo-moon-weinreb.html
148 ;;; (also worth seeing: http://mumble.net/~jar/articles/oo.html )
150 ;; This is the internal, generalized message sending method.
151 ;; Users shouldn't use it! Use the <-foo forms instead.
153 (define-inlinable (%<- wants-reply from-actor to action args message-id in-reply-to)
154 ;; Okay, we need to deal with message ids.
155 ;; Could we get rid of them? :\
156 ;; It seems if we can use eq? and have messages be immutable then
157 ;; it should be possible to identify follow-up replies.
158 ;; If we need to track replies across hive boundaries we could
159 ;; register unique ids across the ambassador barrier.
161 (#(_ _ (? channel? channel) dead?)
162 (let ((message (make-message message-id to
163 (and from-actor (actor-id from-actor))
165 #:wants-reply wants-reply
166 #:in-reply-to in-reply-to)))
169 (put-operation channel message)
170 (wait-operation dead?)))))
171 ;; TODO: put remote addresses here.
172 (#(actor-id hive-id #f #f)
173 ;; Here we'd make a call to our hive...
175 ;; A message sent to nobody goes nowhere.
176 ;; TODO: Should we display a warning here, probably?
179 (define (<- to action . args)
180 (define from-actor (*current-actor*))
181 (%<- #f from-actor to action args
183 ((actor-msg-id-generator from-actor)))
184 (big-random-number-string))
187 ;; TODO: this should abort to the prompt, then check for errors
190 (define (<-wait to action . args)
191 (define prompt (*actor-prompt*))
193 (error "Tried to <-wait without being in an actor's context..."))
195 (let ((reply (abort-to-prompt prompt to action args)))
196 (cond ((eq? action '*error*)
197 (throw 'hive-unresumable-coroutine
198 "Won't resume coroutine; got an *error* as a reply"
200 (else (apply values (message-body reply))))))
203 ;;; Main actor implementation
204 ;;; =========================
206 (define (actor-inheritable-message-handler actor message)
207 (define action (message-action message))
209 (class-rmeta-ref (class-of actor) 'actions action
210 #:equals? eq? #:cache-set! hashq-set!
211 #:cache-ref hashq-ref))
213 (throw 'action-not-found
214 "No appropriate action handler found for actor"
218 (apply method actor message (message-body message)))
220 (define-syntax-rule (build-actions (symbol method) ...)
221 "Construct an alist of (symbol . method), where the method is wrapped
222 with wrap-apply to facilitate live hacking and allow the method definition
223 to come after class definition."
225 (list (cons (quote symbol)
226 (wrap-apply method)) ...)))
228 (define-class <actor> ()
229 ;; An address object... a vector of #(actor-id hive-id inbox-channel dead?)
230 ;; - inbox-channel is the receiving channel (as opposed to actor-inbox-deq)
231 ;; - dead? is a fibers condition variable which is set once this actor
233 (id #:init-keyword #:address
235 ;; The connection to the hive we're connected to.
236 (hive-channel #:init-keyword #:hive-channel
237 #:accessor actor-hive-channel)
239 ;; Our queue to send/receive messages on
240 (inbox-deq #:init-thunk make-channel
241 #:accessor actor-inbox-deq)
243 (msg-id-generator #:init-thunk simple-message-id-generator
244 #:getter actor-msg-id-generator)
246 ;; How we receive and process new messages
247 (message-handler #:init-value actor-inheritable-message-handler
248 ;; @@: There's no reason not to use #:class instead of
249 ;; #:each-subclass anywhere in this file, except for
250 ;; Guile bug #25211 (#:class is broken in Guile 2.2)
251 #:allocation #:each-subclass
252 #:getter actor-message-handler)
255 ;; - #t as in, send the init message, but don't wait (default)
256 ;; - 'wait, as in wait on the init message
257 ;; - #f as in don't bother to init
258 (should-init #:init-value #t
259 #:getter actor-should-init
260 #:allocation #:each-subclass)
262 ;; This is the default, "simple" way to inherit and process messages.
263 (actions #:init-thunk (build-actions)
264 #:allocation #:each-subclass))
266 ;;; Actors may specify an "init" action that occurs before the actor
267 ;;; actually begins to run.
268 ;;; During actor-init!, an actor may send a message to itself or others
269 ;;; via <- but *may not* use <-wait.
270 (define-method (actor-init! (actor <actor>))
273 (define-method (actor-cleanup! (actor <actor>))
276 ;;; Addresses are vectors where the first part is the actor-id and
277 ;;; the second part is the hive-id. This works well enough... they
278 ;;; look decent being pretty-printed.
280 (define (make-address actor-id hive-id channel dead?)
281 (vector actor-id hive-id channel dead?))
283 (define (address-actor-id address)
284 (vector-ref address 0))
286 (define (address-hive-id address)
287 (vector-ref address 1))
289 (define (address-channel address)
290 (vector-ref address 2))
292 (define (address-dead? address)
293 (vector-ref address 3))
295 (define (address->string address)
296 (string-append (address-actor-id address) "@"
297 (address-hive-id address)))
299 (define (address-equal? address1 address2)
300 "Check whether or not the two addresses are equal.
302 This compares the actor-id and hive-id but ignores the channel and
305 (#(actor-id-1 hive-id-1 _ _)
307 (#(actor-id-2 hive-id-2)
308 (and (equal? actor-id-1 actor-id-2)
309 (and (equal? hive-id-1 hive-id-2))))
313 (define (actor-id-actor actor)
314 "Get the actor id component of the actor-id"
315 (address-actor-id (actor-id actor)))
317 (define (actor-id-hive actor)
318 "Get the hive id component of the actor-id"
319 (address-hive-id (actor-id actor)))
321 (define (actor-id-string actor)
322 "Render the full actor id as a human-readable string"
323 (address->string (actor-id actor)))
325 (define (actor-inbox-enq actor)
326 (address-channel (actor-id actor)))
328 (define *current-actor*
331 (define *actor-prompt*
334 (define (actor-main-loop actor)
335 "Main loop of the actor. Loops around, pulling messages off its queue
337 ;; @@: Maybe establish some sort of garbage collection routine for these...
340 (define message-handler
341 (actor-message-handler actor))
343 (address-dead? (actor-id actor)))
344 (define prompt (make-prompt-tag (actor-id-actor actor)))
346 (define (handle-message message)
351 (message-handler actor message))
353 ;; Return reply if necessary
354 (when (message-wants-reply message)
355 (when (message-wants-reply message)
356 (%<- #f actor (message-from message) '*reply*
357 vals ((actor-msg-id-generator actor))
358 (message-id message)))))))
360 (let ((err (current-error-port)))
363 (let ((stack (make-stack #t 4)))
364 (format err "Uncaught exception when handling message ~a:\n"
366 (display-backtrace stack err)
367 (print-exception err (stack-ref stack 0)
370 ;; If the other actor is waiting on a reply, let's let them
371 ;; know there was an error...
372 (when (message-wants-reply message)
373 (%<- #f actor (message-from message) '*error*
374 (list key) ((actor-msg-id-generator actor))
375 (message-id message)))))))))
377 (define (resume-handler message)
378 (define in-reply-to (message-in-reply-to message))
380 ((hash-ref waiting in-reply-to) =>
382 (hash-remove! waiting in-reply-to)
385 (format (current-error-port)
386 "Tried to resume nonexistant message: ~a\n"
387 (message-id message)))))
389 (define halt-or-handle-message
390 ;; It would be nice if we could give priorities to certain operations.
391 ;; halt should always win over getting a message...
393 (wrap-operation (wait-operation dead?)
394 (const #f)) ; halt and return
395 (wrap-operation (get-operation (actor-inbox-deq actor))
397 (call-with-prompt prompt
399 (if (message-in-reply-to message)
400 ;; resume a continuation which was waiting on a reply
401 (resume-handler message)
402 ;; start handling a new message
403 (handle-message message)))
404 ;; Here's where we abort to if we're doing <-wait
405 ;; @@: maybe use match-lambda if we're going to end up
406 ;; handling multiple ~commands
407 (lambda (kont to action message-args)
409 ((actor-msg-id-generator actor)))
410 (hash-set! waiting message-id kont)
411 (%<- #t actor to action message-args message-id #f)))
414 ;; Mutate the parameter; this should be fine since each fiber
415 ;; runs in its own dynamic state with with-dynamic-state.
416 ;; See with-dynamic-state discussion in
417 ;; https://wingolog.org/archives/2017/06/27/growing-fibers
418 (*current-actor* actor)
419 ;; We temporarily set the *actor-prompt* to #f to make sure that
420 ;; actor-init! doesn't try to do a <-wait message (and not accidentally use
421 ;; the parent fiber's *actor-prompt* either.)
424 (*actor-prompt* prompt)
427 (and (perform-operation halt-or-handle-message)
434 (define-syntax-rule (define-actor class inherits
437 (define-class class inherits
438 (actions #:init-thunk (build-actions action ...)
439 #:allocation #:each-subclass)
445 ;;; Every actor has a hive, which keeps track of other actors, manages
446 ;;; cleanup, and performs inter-hive communication.
448 (define-class <hive> ()
449 (id #:init-keyword #:id
451 (actor-registry #:init-thunk make-hash-table
452 #:getter hive-actor-registry)
453 ;; TODO: Rename "ambassadors" to "relays"
454 ;; Ambassadors are used (or will be) for inter-hive communication.
455 ;; These are special actors that know how to route messages to other
457 (ambassadors #:init-thunk make-weak-key-hash-table
458 #:getter hive-ambassadors)
459 (channel #:init-thunk make-channel
460 #:getter hive-channel)
461 (halt? #:init-thunk make-condition
462 #:getter hive-halt?))
464 (define* (make-hive #:key hive-id)
465 (make <hive> #:id (or hive-id
466 (big-random-number-string))))
468 (define (gen-actor-id cookie)
470 (string-append cookie ":" (big-random-number-string))
471 (big-random-number-string)))
473 (define (hive-main-loop hive)
474 "The main loop of the hive. This listens for messages on the hive-channel
475 for certain actions to perform.
477 `messages' here is not the same as a <message> object; these are a list of
478 values, the first value being a symbol"
479 (define channel (hive-channel hive))
480 (define halt? (hive-halt? hive))
481 (define registry (hive-actor-registry hive))
483 ;; not the same as a <message> ;P
484 (define handle-message
486 (('register-actor actor-id address actor)
487 (hash-set! registry actor-id (vector address actor)))
488 ;; Remove the actor from hive
489 (('remove-actor actor-id)
490 (hash-remove! (hive-actor-registry hive) actor-id))
491 (('register-ambassador hive-id ambassador-actor-id)
493 (('unregister-ambassador hive-id ambassador-actor-id)
495 (('forward-message from-actor-id message)
498 (define halt-or-handle
500 (wrap-operation (get-operation channel)
504 (wrap-operation (wait-operation halt?)
508 (and (perform-operation halt-or-handle)
511 (define *current-hive* (make-parameter #f))
513 (define* (spawn-hive proc #:key (hive (make-hive)))
514 "Spawn a hive in a fiber running PROC, passing it the fresh hive"
515 (spawn-fiber (lambda () (hive-main-loop hive)))
518 (define (run-hive proc . args)
519 "Spawn a hive and run it in run-fibers. Takes a PROC as would be passed
520 to spawn-hive... all remaining arguments passed to run-fibers."
526 (define (%create-actor hive-channel hive-id
527 actor-class init-args id-cookie send-init?)
528 (let* ((actor-id (gen-actor-id id-cookie))
529 (dead? (make-condition))
530 (inbox-enq (make-channel))
531 (address (make-address actor-id hive-id
533 (actor (apply make actor-class
534 #:hive-channel hive-channel
537 (should-init (actor-should-init actor)))
539 ;; start the main loop
540 (spawn-fiber (lambda ()
541 ;; start the inbox loop
544 (delivery-agent inbox-enq (actor-inbox-deq actor)
546 ;; this one is decidedly non-parallel, because we want
547 ;; the delivery agent to be in the same thread as its actor
550 (actor-main-loop actor))
553 (put-message hive-channel (list 'register-actor actor-id address actor))
555 ;; return the address
558 (define* (bootstrap-actor hive actor-class #:rest init-args)
559 "Create an actor on HIVE using ACTOR-CLASS passing in INIT-ARGS args"
560 (%create-actor (hive-channel hive) (hive-id hive) actor-class
561 init-args (symbol->string (class-name actor-class))
564 (define* (bootstrap-actor* hive actor-class id-cookie #:rest init-args)
565 "Create an actor, but also allow customizing a 'cookie' added to the id
567 (%create-actor (hive-channel hive) (hive-id hive) actor-class
571 (define* (create-actor from-actor actor-class #:rest init-args)
572 "Create an instance of actor-class. Return the new actor's id.
574 This is the method actors should call directly (unless they want
575 to supply an id-cookie, in which case they should use
577 (%create-actor (actor-hive-channel from-actor) (actor-id-hive from-actor)
578 actor-class init-args #f #t))
581 (define* (create-actor* from-actor actor-class id-cookie #:rest init-args)
582 "Create an instance of actor-class. Return the new actor's id.
584 Like create-actor, but permits supplying an id-cookie."
585 (%create-actor (actor-hive-channel from-actor) (actor-id-hive from-actor)
586 actor-class init-args id-cookie #t))
588 (define* (self-destruct actor #:key (cleanup #t))
589 "Remove an actor from the hive.
591 Unless #:cleanup is set to #f, this will first have the actor handle
592 its '*cleanup* action handler."
593 (signal-condition! (address-dead? (actor-id actor)))
594 (put-message (actor-hive-channel actor) (list 'remove-actor (actor-id-actor actor)))
595 ;; Set *actor-prompt* to nothing to prevent actor-cleanup! from sending
596 ;; a message with <-wait
598 (actor-cleanup! actor))
600 ;; From a patch I sent to Fibers...
601 (define (condition-signalled? cvar)
602 "Return @code{#t} if @var{cvar} has already been signalled.
604 In general you will want to use @code{wait} or @code{wait-operation} to
605 wait on a condition. However, sometimes it is useful to see whether or
606 not a condition has already been signalled without blocking."
607 (atomic-box-ref ((@@ (fibers conditions) condition-signalled?) cvar)))
609 (define (actor-alive? actor)
610 (condition-signalled? (address-dead? (actor-id actor))))