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 ports internal)
27 #:select (port-read-wait-fd port-write-wait-fd))
28 #:use-module (ice-9 pretty-print)
29 #:use-module (ice-9 receive)
30 #:use-module (ice-9 suspendable-ports)
32 #:use-module (fibers channels)
33 #:use-module (fibers conditions)
34 #:use-module (fibers operations)
35 #:use-module (8sync inbox)
36 #:use-module (8sync rmeta-slot)
38 #:export (;; utilities... ought to go in their own module
40 big-random-number-string
48 ;;; Commenting out the <address> type for now;
49 ;;; it may be back when we have better serializers
52 address-actor-id address-hive-id
59 actor-init! actor-cleanup!
68 with-actor-nonblocking-ports
72 ;; ;; There are more methods for the hive, but there's
73 ;; ;; no reason for the outside world to look at them maybe?
75 create-actor create-actor*
80 message-to message-action message-from
81 message-id message-body message-in-reply-to
88 ;; Maybe the wrong place for this, or for it to be exported.
89 ;; But it's used in websockets' server implementation at least...
93 (set! *random-state* (random-state-from-platform))
95 ;; Same size as a uuid4 I think...
96 (define random-number-size (expt 2 128))
98 (define (big-random-number)
99 (random random-number-size))
101 ;; Would be great to get this base64 encoded instead.
102 (define (big-random-number-string)
103 ;; @@: This is slow. Using format here is wasteful.
104 (format #f "~x" (big-random-number)))
106 ;; @@: This is slow-ish. A mere ~275k / second on my (old) machine.
107 ;; The main cost seems to be in number->string.
108 (define (simple-message-id-generator)
109 ;; Prepending this cookie makes message ids unique per hive
110 (let ((prefix (format #f "~x:" (big-random-number)))
113 (set! counter (1+ counter))
114 (string-append prefix (number->string counter)))))
121 (define-record-type <message>
122 (make-message-intern id to from action
123 body in-reply-to wants-reply)
125 ;; @@: message-ids are removed. They could be re-enabled
126 ;; if we had thread-safe promises...
127 (id message-id) ; id of this message
128 (to message-to) ; actor id this is going to
129 (from message-from) ; actor id of sender
130 (action message-action) ; action (a symbol) to be handled
131 (body message-body) ; argument list "body" of message
132 (in-reply-to message-in-reply-to) ; message id this is in reply to, if any
133 (wants-reply message-wants-reply)) ; whether caller is waiting for reply
136 (define* (make-message id to from action body
137 #:key in-reply-to wants-reply)
138 (make-message-intern id to from action body
139 in-reply-to wants-reply))
141 (define (kwarg-list-to-alist args)
142 (let loop ((remaining args)
145 (((? keyword? key) val rest ...)
147 (cons (cons (keyword->symbol key) val)
150 (_ (throw 'invalid-kwarg-list
151 "Invalid keyword argument list"
155 ;;; See: https://web.archive.org/web/20081223021934/http://mumble.net/~jar/articles/oo-moon-weinreb.html
156 ;;; (also worth seeing: http://mumble.net/~jar/articles/oo.html )
158 ;; This is the internal, generalized message sending method.
159 ;; Users shouldn't use it! Use the <-foo forms instead.
161 (define-inlinable (%<- wants-reply from-actor to action args message-id in-reply-to)
162 ;; Okay, we need to deal with message ids.
163 ;; Could we get rid of them? :\
164 ;; It seems if we can use eq? and have messages be immutable then
165 ;; it should be possible to identify follow-up replies.
166 ;; If we need to track replies across hive boundaries we could
167 ;; register unique ids across the ambassador barrier.
169 (#(_ _ (? channel? channel) dead?)
170 (let ((message (make-message message-id to
171 (and from-actor (actor-id from-actor))
173 #:wants-reply wants-reply
174 #:in-reply-to in-reply-to)))
177 (put-operation channel message)
178 (wait-operation dead?)))))
179 ;; TODO: put remote addresses here.
180 (#(actor-id hive-id #f #f)
181 ;; Here we'd make a call to our hive...
183 ;; A message sent to nobody goes nowhere.
184 ;; TODO: Should we display a warning here, probably?
187 (define (<- to action . args)
188 (define from-actor (*current-actor*))
189 (%<- #f from-actor to action args
191 ((actor-msg-id-generator from-actor)))
192 (big-random-number-string))
195 ;; TODO: this should abort to the prompt, then check for errors
198 (define (<-wait to action . args)
199 (define prompt (*actor-prompt*))
201 (error "Tried to <-wait without being in an actor's context..."))
203 (let ((reply (abort-to-prompt prompt '<-wait to action args)))
204 (cond ((eq? action '*error*)
205 (throw 'hive-unresumable-coroutine
206 "Won't resume coroutine; got an *error* as a reply"
208 (else (apply values (message-body reply))))))
211 ;;; Main actor implementation
212 ;;; =========================
214 (define (actor-inheritable-message-handler actor message)
215 (define action (message-action message))
217 (class-rmeta-ref (class-of actor) 'actions action
218 #:equals? eq? #:cache-set! hashq-set!
219 #:cache-ref hashq-ref))
221 (throw 'action-not-found
222 "No appropriate action handler found for actor"
226 (apply method actor message (message-body message)))
228 (define-syntax-rule (live-wrap body)
229 "Wrap possibly multi-value function in a procedure, applies all arguments"
233 (define-syntax-rule (build-actions (symbol method) ...)
234 "Construct an alist of (symbol . method), where the method is wrapped
235 with `live-wrap' to facilitate live hacking and allow the method definition
236 to come after class definition."
238 (list (cons (quote symbol)
239 (live-wrap method)) ...)))
241 (define-class <actor> ()
242 ;; An address object... a vector of #(actor-id hive-id inbox-channel dead?)
243 ;; - inbox-channel is the receiving channel (as opposed to actor-inbox-deq)
244 ;; - dead? is a fibers condition variable which is set once this actor
246 (id #:init-keyword #:address
249 ;; Our queue to send/receive messages on
250 (inbox-deq #:init-thunk make-channel
251 #:accessor actor-inbox-deq)
253 (msg-id-generator #:init-thunk simple-message-id-generator
254 #:getter actor-msg-id-generator)
256 ;; How we receive and process new messages
257 (message-handler #:init-value actor-inheritable-message-handler
258 ;; @@: There's no reason not to use #:class instead of
259 ;; #:each-subclass anywhere in this file, except for
260 ;; Guile bug #25211 (#:class is broken in Guile 2.2)
261 #:allocation #:each-subclass
262 #:getter actor-message-handler)
265 ;; - #t as in, send the init message, but don't wait (default)
266 ;; - 'wait, as in wait on the init message
267 ;; - #f as in don't bother to init
268 (should-init #:init-value #t
269 #:getter actor-should-init
270 #:allocation #:each-subclass)
272 ;; This is the default, "simple" way to inherit and process messages.
273 (actions #:init-thunk (build-actions)
274 #:allocation #:each-subclass))
276 ;;; Actors may specify an "init" action that occurs before the actor
277 ;;; actually begins to run.
278 ;;; During actor-init!, an actor may send a message to itself or others
279 ;;; via <- but *may not* use <-wait.
280 (define-method (actor-init! (actor <actor>))
283 (define-method (actor-cleanup! (actor <actor>))
286 ;;; Addresses are vectors where the first part is the actor-id and
287 ;;; the second part is the hive-id. This works well enough... they
288 ;;; look decent being pretty-printed.
290 (define (make-address actor-id hive-id channel dead?)
291 (vector actor-id hive-id channel dead?))
293 (define (address-actor-id address)
294 (vector-ref address 0))
296 (define (address-hive-id address)
297 (vector-ref address 1))
299 (define (address-channel address)
300 (vector-ref address 2))
302 (define (address-dead? address)
303 (vector-ref address 3))
305 (define (address->string address)
306 (string-append (address-actor-id address) "@"
307 (address-hive-id address)))
309 (define (address-equal? address1 address2)
310 "Check whether or not the two addresses are equal.
312 This compares the actor-id and hive-id but ignores the channel and
315 (#(actor-id-1 hive-id-1 _ _)
317 (#(actor-id-2 hive-id-2)
318 (and (equal? actor-id-1 actor-id-2)
319 (and (equal? hive-id-1 hive-id-2))))
323 (define (actor-id-actor actor)
324 "Get the actor id component of the actor-id"
325 (address-actor-id (actor-id actor)))
327 (define (actor-id-hive actor)
328 "Get the hive id component of the actor-id"
329 (address-hive-id (actor-id actor)))
331 (define (actor-id-string actor)
332 "Render the full actor id as a human-readable string"
333 (address->string (actor-id actor)))
335 (define (actor-inbox-enq actor)
336 (address-channel (actor-id actor)))
338 (define *current-actor*
341 (define *actor-prompt*
344 (define *resume-io-channel*
347 (define (actor-main-loop actor)
348 "Main loop of the actor. Loops around, pulling messages off its queue
350 ;; @@: Maybe establish some sort of garbage collection routine for these...
353 (define message-handler
354 (actor-message-handler actor))
356 (address-dead? (actor-id actor)))
357 (define prompt (make-prompt-tag (actor-id-actor actor)))
358 ;; Not always used, only if with-actor-nonblocking-ports is used
359 (define resume-io-channel
362 (define (handle-message message)
367 (message-handler actor message))
369 ;; Return reply if necessary
370 (when (message-wants-reply message)
371 (when (message-wants-reply message)
372 (%<- #f actor (message-from message) '*reply*
373 vals ((actor-msg-id-generator actor))
374 (message-id message)))))))
376 (let ((err (current-error-port)))
379 (let ((stack (make-stack #t 4)))
380 (format err "Uncaught exception when handling message ~a:\n"
382 (display-backtrace stack err)
383 (print-exception err (stack-ref stack 0)
386 ;; If the other actor is waiting on a reply, let's let them
387 ;; know there was an error...
388 (when (message-wants-reply message)
389 (%<- #f actor (message-from message) '*error*
390 (list key) ((actor-msg-id-generator actor))
391 (message-id message)))))))))
393 (define (resume-handler message)
394 (define in-reply-to (message-in-reply-to message))
396 ((hash-ref waiting in-reply-to) =>
398 (hash-remove! waiting in-reply-to)
401 (format (current-error-port)
402 "Tried to resume nonexistant message: ~a\n"
403 (message-id message)))))
405 (define (call-with-actor-prompt thunk)
406 (call-with-prompt prompt
408 ;; Here's where we abort to if we're doing <-wait
409 ;; @@: maybe use match-lambda if we're going to end up
410 ;; handling multiple ~commands
412 ((kont '<-wait to action message-args)
414 ((actor-msg-id-generator actor)))
415 (hash-set! waiting message-id kont)
416 (%<- #t actor to action message-args message-id #f))
420 (define halt-or-handle-message
421 ;; It would be nice if we could give priorities to certain operations.
422 ;; halt should always win over getting a message...
424 (wrap-operation (wait-operation dead?)
425 (const #f)) ; halt and return
426 (wrap-operation (get-operation (actor-inbox-deq actor))
428 (call-with-actor-prompt
430 (if (message-in-reply-to message)
431 ;; resume a continuation which was waiting on a reply
432 (resume-handler message)
433 ;; start handling a new message
434 (handle-message message))))
436 (wrap-operation (get-operation resume-io-channel)
438 (call-with-actor-prompt
443 ;; Mutate the parameter; this should be fine since each fiber
444 ;; runs in its own dynamic state with with-dynamic-state.
445 ;; See with-dynamic-state discussion in
446 ;; https://wingolog.org/archives/2017/06/27/growing-fibers
447 (*current-actor* actor)
448 (*resume-io-channel* resume-io-channel)
450 ;; We temporarily set the *actor-prompt* to #f to make sure that
451 ;; actor-init! doesn't try to do a <-wait message (and not accidentally use
452 ;; the parent fiber's *actor-prompt* either.)
455 (*actor-prompt* prompt)
458 (and (perform-operation halt-or-handle-message)
462 ;; @@: So in order for this to work, we're going to have to add
463 ;; another channel to actors, which is resumable i/o. We'll have to
464 ;; spawn a fiber that wakes up a thunk on the actor when its port is
465 ;; available. Funky...
467 (define (%suspend-io-to-actor wait-for-read/write)
469 (define prompt (*actor-prompt*))
470 (define resume-channel (*resume-io-channel*))
471 (define (run-at-prompt k)
474 (wait-for-read/write port)
475 ;; okay, we're awake again, tell the actor to resume this
477 (put-message resume-channel k))
480 (error "Attempt to abort to actor prompt outside of actor"))
481 (abort-to-prompt (*actor-prompt*)
482 'run-me run-at-prompt)))
484 (define suspend-read-to-actor
485 (%suspend-io-to-actor (@@ (fibers) wait-for-readable)))
487 (define suspend-write-to-actor
488 (%suspend-io-to-actor (@@ (fibers) wait-for-writable)))
490 (define (with-actor-nonblocking-ports thunk)
491 "Runs THUNK in dynamic context in which attempting to read/write
492 from a port that would otherwise block an actor's correspondence with
493 other actors (note that reading from a nonblocking port should never
494 block other fibers) will instead permit reading other messages while
495 I/O is waiting to complete.
497 Note that currently "
498 (parameterize ((current-read-waiter suspend-read-to-actor)
499 (current-write-waiter suspend-write-to-actor))
502 (define (actor-spawn-fiber thunk . args)
503 "Spawn a fiber from an actor but unset actor-machinery-specific
508 (*resume-io-channel* #f)
518 (define-syntax-rule (define-actor class inherits
521 (define-class class inherits
522 (actions #:init-thunk (build-actions action ...)
523 #:allocation #:each-subclass)
529 ;;; Every actor has a hive, which keeps track of other actors, manages
530 ;;; cleanup, and performs inter-hive communication.
532 ;; TODO: Make this a srfi-9 record type
533 (define-class <hive> ()
534 (id #:init-keyword #:id
536 (actor-registry #:init-thunk make-hash-table
537 #:getter hive-actor-registry)
538 ;; TODO: Rename "ambassadors" to "relays"
539 ;; Ambassadors are used (or will be) for inter-hive communication.
540 ;; These are special actors that know how to route messages to other
542 (ambassadors #:init-thunk make-weak-key-hash-table
543 #:getter hive-ambassadors)
544 (channel #:init-thunk make-channel
545 #:getter hive-channel)
546 (halt? #:init-thunk make-condition
547 #:getter hive-halt?))
549 (define* (make-hive #:key hive-id)
550 (make <hive> #:id (or hive-id
551 (big-random-number-string))))
553 (define (gen-actor-id cookie)
555 (string-append cookie ":" (big-random-number-string))
556 (big-random-number-string)))
558 (define (hive-main-loop hive)
559 "The main loop of the hive. This listens for messages on the hive-channel
560 for certain actions to perform.
562 `messages' here is not the same as a <message> object; these are a list of
563 values, the first value being a symbol"
564 (define channel (hive-channel hive))
565 (define halt? (hive-halt? hive))
566 (define registry (hive-actor-registry hive))
568 ;; not the same as a <message> ;P
569 (define handle-message
571 (('register-actor actor-id address actor)
572 (hash-set! registry actor-id (vector address actor)))
573 ;; Remove the actor from hive
574 (('remove-actor actor-id)
575 (hash-remove! (hive-actor-registry hive) actor-id))
576 (('register-ambassador hive-id ambassador-actor-id)
578 (('unregister-ambassador hive-id ambassador-actor-id)
580 (('forward-message from-actor-id message)
583 (define halt-or-handle
585 (wrap-operation (get-operation channel)
589 (wrap-operation (wait-operation halt?)
593 (and (perform-operation halt-or-handle)
596 (define *hive-id* (make-parameter #f))
597 (define *hive-channel* (make-parameter #f))
599 ;; @@: Should we halt the hive either at the end of spawn-hive or run-hive?
600 (define* (spawn-hive proc #:key (hive (make-hive)))
601 "Spawn a hive and run PROC, passing it the fresh hive and establishing
602 a dynamic context surrounding the hive."
603 (spawn-fiber (lambda () (hive-main-loop hive)))
604 (parameterize ((*hive-id* (hive-id hive))
605 (*hive-channel* (hive-channel hive)))
608 (define (run-hive proc . args)
609 "Spawn a hive and run it in run-fibers. Takes a PROC as would be passed
610 to spawn-hive... all remaining arguments passed to run-fibers."
616 (define (%create-actor actor-class init-args id-cookie send-init?)
617 (let* ((hive-channel (*hive-channel*))
618 (hive-id (*hive-id*))
619 (actor-id (gen-actor-id id-cookie))
620 (dead? (make-condition))
621 (inbox-enq (make-channel))
622 (address (make-address actor-id hive-id
624 (actor (apply make actor-class
627 (should-init (actor-should-init actor)))
629 ;; start the main loop
630 (spawn-fiber (lambda ()
631 ;; start the inbox loop
634 (delivery-agent inbox-enq (actor-inbox-deq actor)
636 ;; this one is decidedly non-parallel, because we want
637 ;; the delivery agent to be in the same thread as its actor
640 (actor-main-loop actor))
643 (put-message hive-channel (list 'register-actor actor-id address actor))
645 ;; return the address
648 (define* (create-actor actor-class #:rest init-args)
649 "Create an instance of actor-class. Return the new actor's id.
651 This is the method actors should call directly (unless they want
652 to supply an id-cookie, in which case they should use
654 (%create-actor actor-class init-args #f #t))
657 (define* (create-actor* actor-class id-cookie #:rest init-args)
658 "Create an instance of actor-class. Return the new actor's id.
660 Like create-actor, but permits supplying an id-cookie."
661 (%create-actor actor-class init-args id-cookie #t))
663 (define* (self-destruct actor #:key (cleanup #t))
664 "Remove an actor from the hive.
666 Unless #:cleanup is set to #f, this will first have the actor handle
667 its '*cleanup* action handler."
668 (signal-condition! (address-dead? (actor-id actor)))
669 (put-message (*hive-channel*) (list 'remove-actor (actor-id-actor actor)))
670 ;; Set *actor-prompt* to nothing to prevent actor-cleanup! from sending
671 ;; a message with <-wait
673 (actor-cleanup! actor))
675 ;; From a patch I sent to Fibers...
676 (define (condition-signalled? cvar)
677 "Return @code{#t} if @var{cvar} has already been signalled.
679 In general you will want to use @code{wait} or @code{wait-operation} to
680 wait on a condition. However, sometimes it is useful to see whether or
681 not a condition has already been signalled without blocking."
682 (atomic-box-ref ((@@ (fibers conditions) condition-signalled?) cvar)))
684 (define (actor-alive? actor)
685 (condition-signalled? (address-dead? (actor-id actor))))