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
46 ;;; Commenting out the <address> type for now;
47 ;;; it may be back when we have better serializers
50 address-actor-id address-hive-id
57 actor-init! actor-cleanup!
66 with-actor-nonblocking-ports
70 ;; ;; There are more methods for the hive, but there's
71 ;; ;; no reason for the outside world to look at them maybe?
73 create-actor create-actor*
78 message-to message-action message-from
79 message-id message-body message-in-reply-to
87 (set! *random-state* (random-state-from-platform))
89 ;; Same size as a uuid4 I think...
90 (define random-number-size (expt 2 128))
92 (define (big-random-number)
93 (random random-number-size))
95 ;; Would be great to get this base64 encoded instead.
96 (define (big-random-number-string)
97 ;; @@: This is slow. Using format here is wasteful.
98 (format #f "~x" (big-random-number)))
100 ;; @@: This is slow-ish. A mere ~275k / second on my (old) machine.
101 ;; The main cost seems to be in number->string.
102 (define (simple-message-id-generator)
103 ;; Prepending this cookie makes message ids unique per hive
104 (let ((prefix (format #f "~x:" (big-random-number)))
107 (set! counter (1+ counter))
108 (string-append prefix (number->string counter)))))
115 (define-record-type <message>
116 (make-message-intern id to from action
117 body in-reply-to wants-reply)
119 ;; @@: message-ids are removed. They could be re-enabled
120 ;; if we had thread-safe promises...
121 (id message-id) ; id of this message
122 (to message-to) ; actor id this is going to
123 (from message-from) ; actor id of sender
124 (action message-action) ; action (a symbol) to be handled
125 (body message-body) ; argument list "body" of message
126 (in-reply-to message-in-reply-to) ; message id this is in reply to, if any
127 (wants-reply message-wants-reply)) ; whether caller is waiting for reply
130 (define* (make-message id to from action body
131 #:key in-reply-to wants-reply)
132 (make-message-intern id to from action body
133 in-reply-to wants-reply))
135 (define (kwarg-list-to-alist args)
136 (let loop ((remaining args)
139 (((? keyword? key) val rest ...)
141 (cons (cons (keyword->symbol key) val)
144 (_ (throw 'invalid-kwarg-list
145 "Invalid keyword argument list"
149 ;;; See: https://web.archive.org/web/20081223021934/http://mumble.net/~jar/articles/oo-moon-weinreb.html
150 ;;; (also worth seeing: http://mumble.net/~jar/articles/oo.html )
152 ;; This is the internal, generalized message sending method.
153 ;; Users shouldn't use it! Use the <-foo forms instead.
155 (define-inlinable (%<- wants-reply from-actor to action args message-id in-reply-to)
156 ;; Okay, we need to deal with message ids.
157 ;; Could we get rid of them? :\
158 ;; It seems if we can use eq? and have messages be immutable then
159 ;; it should be possible to identify follow-up replies.
160 ;; If we need to track replies across hive boundaries we could
161 ;; register unique ids across the ambassador barrier.
163 (#(_ _ (? channel? channel) dead?)
164 (let ((message (make-message message-id to
165 (and from-actor (actor-id from-actor))
167 #:wants-reply wants-reply
168 #:in-reply-to in-reply-to)))
171 (put-operation channel message)
172 (wait-operation dead?)))))
173 ;; TODO: put remote addresses here.
174 (#(actor-id hive-id #f #f)
175 ;; Here we'd make a call to our hive...
177 ;; A message sent to nobody goes nowhere.
178 ;; TODO: Should we display a warning here, probably?
181 (define (<- to action . args)
182 (define from-actor (*current-actor*))
183 (%<- #f from-actor to action args
185 ((actor-msg-id-generator from-actor)))
186 (big-random-number-string))
189 ;; TODO: this should abort to the prompt, then check for errors
192 (define (<-wait to action . args)
193 (define prompt (*actor-prompt*))
195 (error "Tried to <-wait without being in an actor's context..."))
197 (let ((reply (abort-to-prompt prompt '<-wait to action args)))
198 (cond ((eq? action '*error*)
199 (throw 'hive-unresumable-coroutine
200 "Won't resume coroutine; got an *error* as a reply"
202 (else (apply values (message-body reply))))))
205 ;;; Main actor implementation
206 ;;; =========================
208 (define (actor-inheritable-message-handler actor message)
209 (define action (message-action message))
211 (class-rmeta-ref (class-of actor) 'actions action
212 #:equals? eq? #:cache-set! hashq-set!
213 #:cache-ref hashq-ref))
215 (throw 'action-not-found
216 "No appropriate action handler found for actor"
220 (apply method actor message (message-body message)))
222 (define-syntax-rule (wrap-apply body)
223 "Wrap possibly multi-value function in a procedure, applies all arguments"
227 (define-syntax-rule (build-actions (symbol method) ...)
228 "Construct an alist of (symbol . method), where the method is wrapped
229 with wrap-apply to facilitate live hacking and allow the method definition
230 to come after class definition."
232 (list (cons (quote symbol)
233 (wrap-apply method)) ...)))
235 (define-class <actor> ()
236 ;; An address object... a vector of #(actor-id hive-id inbox-channel dead?)
237 ;; - inbox-channel is the receiving channel (as opposed to actor-inbox-deq)
238 ;; - dead? is a fibers condition variable which is set once this actor
240 (id #:init-keyword #:address
243 ;; Our queue to send/receive messages on
244 (inbox-deq #:init-thunk make-channel
245 #:accessor actor-inbox-deq)
247 (msg-id-generator #:init-thunk simple-message-id-generator
248 #:getter actor-msg-id-generator)
250 ;; How we receive and process new messages
251 (message-handler #:init-value actor-inheritable-message-handler
252 ;; @@: There's no reason not to use #:class instead of
253 ;; #:each-subclass anywhere in this file, except for
254 ;; Guile bug #25211 (#:class is broken in Guile 2.2)
255 #:allocation #:each-subclass
256 #:getter actor-message-handler)
259 ;; - #t as in, send the init message, but don't wait (default)
260 ;; - 'wait, as in wait on the init message
261 ;; - #f as in don't bother to init
262 (should-init #:init-value #t
263 #:getter actor-should-init
264 #:allocation #:each-subclass)
266 ;; This is the default, "simple" way to inherit and process messages.
267 (actions #:init-thunk (build-actions)
268 #:allocation #:each-subclass))
270 ;;; Actors may specify an "init" action that occurs before the actor
271 ;;; actually begins to run.
272 ;;; During actor-init!, an actor may send a message to itself or others
273 ;;; via <- but *may not* use <-wait.
274 (define-method (actor-init! (actor <actor>))
277 (define-method (actor-cleanup! (actor <actor>))
280 ;;; Addresses are vectors where the first part is the actor-id and
281 ;;; the second part is the hive-id. This works well enough... they
282 ;;; look decent being pretty-printed.
284 (define (make-address actor-id hive-id channel dead?)
285 (vector actor-id hive-id channel dead?))
287 (define (address-actor-id address)
288 (vector-ref address 0))
290 (define (address-hive-id address)
291 (vector-ref address 1))
293 (define (address-channel address)
294 (vector-ref address 2))
296 (define (address-dead? address)
297 (vector-ref address 3))
299 (define (address->string address)
300 (string-append (address-actor-id address) "@"
301 (address-hive-id address)))
303 (define (address-equal? address1 address2)
304 "Check whether or not the two addresses are equal.
306 This compares the actor-id and hive-id but ignores the channel and
309 (#(actor-id-1 hive-id-1 _ _)
311 (#(actor-id-2 hive-id-2)
312 (and (equal? actor-id-1 actor-id-2)
313 (and (equal? hive-id-1 hive-id-2))))
317 (define (actor-id-actor actor)
318 "Get the actor id component of the actor-id"
319 (address-actor-id (actor-id actor)))
321 (define (actor-id-hive actor)
322 "Get the hive id component of the actor-id"
323 (address-hive-id (actor-id actor)))
325 (define (actor-id-string actor)
326 "Render the full actor id as a human-readable string"
327 (address->string (actor-id actor)))
329 (define (actor-inbox-enq actor)
330 (address-channel (actor-id actor)))
332 (define *current-actor*
335 (define *actor-prompt*
338 (define *resume-io-channel*
341 (define (actor-main-loop actor)
342 "Main loop of the actor. Loops around, pulling messages off its queue
344 ;; @@: Maybe establish some sort of garbage collection routine for these...
347 (define message-handler
348 (actor-message-handler actor))
350 (address-dead? (actor-id actor)))
351 (define prompt (make-prompt-tag (actor-id-actor actor)))
352 ;; Not always used, only if with-actor-nonblocking-ports is used
353 (define resume-io-channel
356 (define (handle-message message)
361 (message-handler actor message))
363 ;; Return reply if necessary
364 (when (message-wants-reply message)
365 (when (message-wants-reply message)
366 (%<- #f actor (message-from message) '*reply*
367 vals ((actor-msg-id-generator actor))
368 (message-id message)))))))
370 (let ((err (current-error-port)))
373 (let ((stack (make-stack #t 4)))
374 (format err "Uncaught exception when handling message ~a:\n"
376 (display-backtrace stack err)
377 (print-exception err (stack-ref stack 0)
380 ;; If the other actor is waiting on a reply, let's let them
381 ;; know there was an error...
382 (when (message-wants-reply message)
383 (%<- #f actor (message-from message) '*error*
384 (list key) ((actor-msg-id-generator actor))
385 (message-id message)))))))))
387 (define (resume-handler message)
388 (define in-reply-to (message-in-reply-to message))
390 ((hash-ref waiting in-reply-to) =>
392 (hash-remove! waiting in-reply-to)
395 (format (current-error-port)
396 "Tried to resume nonexistant message: ~a\n"
397 (message-id message)))))
399 (define (call-with-actor-prompt thunk)
400 (call-with-prompt prompt
402 ;; Here's where we abort to if we're doing <-wait
403 ;; @@: maybe use match-lambda if we're going to end up
404 ;; handling multiple ~commands
406 ((kont '<-wait to action message-args)
408 ((actor-msg-id-generator actor)))
409 (hash-set! waiting message-id kont)
410 (%<- #t actor to action message-args message-id #f))
414 (define halt-or-handle-message
415 ;; It would be nice if we could give priorities to certain operations.
416 ;; halt should always win over getting a message...
418 (wrap-operation (wait-operation dead?)
419 (const #f)) ; halt and return
420 (wrap-operation (get-operation (actor-inbox-deq actor))
422 (call-with-actor-prompt
424 (if (message-in-reply-to message)
425 ;; resume a continuation which was waiting on a reply
426 (resume-handler message)
427 ;; start handling a new message
428 (handle-message message))))
430 (wrap-operation (get-operation resume-io-channel)
432 (call-with-actor-prompt
437 ;; Mutate the parameter; this should be fine since each fiber
438 ;; runs in its own dynamic state with with-dynamic-state.
439 ;; See with-dynamic-state discussion in
440 ;; https://wingolog.org/archives/2017/06/27/growing-fibers
441 (*current-actor* actor)
442 (*resume-io-channel* resume-io-channel)
444 ;; We temporarily set the *actor-prompt* to #f to make sure that
445 ;; actor-init! doesn't try to do a <-wait message (and not accidentally use
446 ;; the parent fiber's *actor-prompt* either.)
449 (*actor-prompt* prompt)
452 (and (perform-operation halt-or-handle-message)
456 ;; @@: So in order for this to work, we're going to have to add
457 ;; another channel to actors, which is resumable i/o. We'll have to
458 ;; spawn a fiber that wakes up a thunk on the actor when its port is
459 ;; available. Funky...
461 (define (%suspend-io-to-actor wait-for-read/write)
463 (define prompt (*actor-prompt*))
464 (define resume-channel (*resume-io-channel*))
465 (define (run-at-prompt k)
468 (wait-for-read/write port)
469 ;; okay, we're awake again, tell the actor to resume this
471 (put-message resume-channel k))
474 (error "Attempt to abort to actor prompt outside of actor"))
475 (abort-to-prompt (*actor-prompt*)
476 'run-me run-at-prompt)))
478 (define suspend-read-to-actor
479 (%suspend-io-to-actor (@@ (fibers) wait-for-readable)))
481 (define suspend-write-to-actor
482 (%suspend-io-to-actor (@@ (fibers) wait-for-writable)))
484 (define (with-actor-nonblocking-ports thunk)
485 "Runs THUNK in dynamic context in which attempting to read/write
486 from a port that would otherwise block an actor's correspondence with
487 other actors (note that reading from a nonblocking port should never
488 block other fibers) will instead permit reading other messages while
489 I/O is waiting to complete.
491 Note that currently "
492 (parameterize ((current-read-waiter suspend-read-to-actor)
493 (current-write-waiter suspend-write-to-actor))
496 (define (actor-spawn-fiber thunk . args)
497 "Spawn a fiber from an actor but unset actor-machinery-specific
502 (*resume-io-channel* #f)
512 (define-syntax-rule (define-actor class inherits
515 (define-class class inherits
516 (actions #:init-thunk (build-actions action ...)
517 #:allocation #:each-subclass)
523 ;;; Every actor has a hive, which keeps track of other actors, manages
524 ;;; cleanup, and performs inter-hive communication.
526 ;; TODO: Make this a srfi-9 record type
527 (define-class <hive> ()
528 (id #:init-keyword #:id
530 (actor-registry #:init-thunk make-hash-table
531 #:getter hive-actor-registry)
532 ;; TODO: Rename "ambassadors" to "relays"
533 ;; Ambassadors are used (or will be) for inter-hive communication.
534 ;; These are special actors that know how to route messages to other
536 (ambassadors #:init-thunk make-weak-key-hash-table
537 #:getter hive-ambassadors)
538 (channel #:init-thunk make-channel
539 #:getter hive-channel)
540 (halt? #:init-thunk make-condition
541 #:getter hive-halt?))
543 (define* (make-hive #:key hive-id)
544 (make <hive> #:id (or hive-id
545 (big-random-number-string))))
547 (define (gen-actor-id cookie)
549 (string-append cookie ":" (big-random-number-string))
550 (big-random-number-string)))
552 (define (hive-main-loop hive)
553 "The main loop of the hive. This listens for messages on the hive-channel
554 for certain actions to perform.
556 `messages' here is not the same as a <message> object; these are a list of
557 values, the first value being a symbol"
558 (define channel (hive-channel hive))
559 (define halt? (hive-halt? hive))
560 (define registry (hive-actor-registry hive))
562 ;; not the same as a <message> ;P
563 (define handle-message
565 (('register-actor actor-id address actor)
566 (hash-set! registry actor-id (vector address actor)))
567 ;; Remove the actor from hive
568 (('remove-actor actor-id)
569 (hash-remove! (hive-actor-registry hive) actor-id))
570 (('register-ambassador hive-id ambassador-actor-id)
572 (('unregister-ambassador hive-id ambassador-actor-id)
574 (('forward-message from-actor-id message)
577 (define halt-or-handle
579 (wrap-operation (get-operation channel)
583 (wrap-operation (wait-operation halt?)
587 (and (perform-operation halt-or-handle)
590 (define *hive-id* (make-parameter #f))
591 (define *hive-channel* (make-parameter #f))
593 ;; @@: Should we halt the hive either at the end of spawn-hive or run-hive?
594 (define* (spawn-hive proc #:key (hive (make-hive)))
595 "Spawn a hive and run PROC, passing it the fresh hive and establishing
596 a dynamic context surrounding the hive."
597 (spawn-fiber (lambda () (hive-main-loop hive)))
598 (parameterize ((*hive-id* (hive-id hive))
599 (*hive-channel* (hive-channel hive)))
602 (define (run-hive proc . args)
603 "Spawn a hive and run it in run-fibers. Takes a PROC as would be passed
604 to spawn-hive... all remaining arguments passed to run-fibers."
610 (define (%create-actor actor-class init-args id-cookie send-init?)
611 (let* ((hive-channel (*hive-channel*))
612 (hive-id (*hive-id*))
613 (actor-id (gen-actor-id id-cookie))
614 (dead? (make-condition))
615 (inbox-enq (make-channel))
616 (address (make-address actor-id hive-id
618 (actor (apply make actor-class
621 (should-init (actor-should-init actor)))
623 ;; start the main loop
624 (spawn-fiber (lambda ()
625 ;; start the inbox loop
628 (delivery-agent inbox-enq (actor-inbox-deq actor)
630 ;; this one is decidedly non-parallel, because we want
631 ;; the delivery agent to be in the same thread as its actor
634 (actor-main-loop actor))
637 (put-message hive-channel (list 'register-actor actor-id address actor))
639 ;; return the address
642 (define* (create-actor actor-class #:rest init-args)
643 "Create an instance of actor-class. Return the new actor's id.
645 This is the method actors should call directly (unless they want
646 to supply an id-cookie, in which case they should use
648 (%create-actor actor-class init-args #f #t))
651 (define* (create-actor* actor-class id-cookie #:rest init-args)
652 "Create an instance of actor-class. Return the new actor's id.
654 Like create-actor, but permits supplying an id-cookie."
655 (%create-actor actor-class init-args id-cookie #t))
657 (define* (self-destruct actor #:key (cleanup #t))
658 "Remove an actor from the hive.
660 Unless #:cleanup is set to #f, this will first have the actor handle
661 its '*cleanup* action handler."
662 (signal-condition! (address-dead? (actor-id actor)))
663 (put-message (*hive-channel*) (list 'remove-actor (actor-id-actor actor)))
664 ;; Set *actor-prompt* to nothing to prevent actor-cleanup! from sending
665 ;; a message with <-wait
667 (actor-cleanup! actor))
669 ;; From a patch I sent to Fibers...
670 (define (condition-signalled? cvar)
671 "Return @code{#t} if @var{cvar} has already been signalled.
673 In general you will want to use @code{wait} or @code{wait-operation} to
674 wait on a condition. However, sometimes it is useful to see whether or
675 not a condition has already been signalled without blocking."
676 (atomic-box-ref ((@@ (fibers conditions) condition-signalled?) cvar)))
678 (define (actor-alive? actor)
679 (condition-signalled? (address-dead? (actor-id actor))))