;; RUN: wast --assert default --snapshot tests/snapshots % -f stack-switching
;; Actors
;; actor interface
(module $actor
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
;; self : [i32] -> []
;; spawn : [cont ([] -> [])] -> [i32]
;; send : [i32 i32] -> []
;; recv : [] -> [i32]
(tag $self (export "self") (result i32))
(tag $spawn (export "spawn") (param (ref $cont)) (result i32))
(tag $send (export "send") (param i32 i32))
(tag $recv (export "recv") (result i32))
)
(register "actor")
;; a simple example - pass a message through a chain of actors
(module $chain
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $i-func (func (param i32))) ;; [i32] -> []
(type $i-cont (cont $i-func)) ;; cont ([i32] -> [])
;; self : [i32] -> []
;; spawn : [cont ([] -> [])] -> [i32]
;; send : [i32 i32] -> []
;; recv : [] -> [i32]
(tag $self (import "actor" "self") (result i32))
(tag $spawn (import "actor" "spawn") (param (ref $cont)) (result i32))
(tag $send (import "actor" "send") (param i32 i32))
(tag $recv (import "actor" "recv") (result i32))
(elem declare func $next)
(func $log (import "spectest" "print_i32") (param i32))
(func $next (param $p i32)
(local $s i32)
(local.set $s (suspend $recv))
(call $log (i32.const -1))
(suspend $send (local.get $s) (local.get $p))
)
;; send the message 42 through a chain of n actors
(func $chain (export "chain") (param $n i32)
(local $p i32)
(local.set $p (suspend $self))
(loop $l
(if (i32.eqz (local.get $n))
(then (suspend $send (i32.const 42) (local.get $p)))
(else (local.set $p (suspend $spawn (cont.bind $i-cont $cont (local.get $p) (cont.new $i-cont (ref.func $next)))))
(local.set $n (i32.sub (local.get $n) (i32.const 1)))
(br $l))
)
)
(call $log (suspend $recv))
)
)
(register "chain")
;; queues of threads and mailboxes
(module $queue
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(func $log (import "spectest" "print_i32") (param i32))
;; table (threads) and memory (mailboxes) as simple queues
(table $queue 0 (ref null $cont))
(memory 1)
(tag $too-many-mailboxes)
(global $qdelta i32 (i32.const 10))
(global $qback-k (mut i32) (i32.const 0))
(global $qfront-k (mut i32) (i32.const 0))
(func $queue-empty-k (export "queue-empty") (result i32)
(i32.eq (global.get $qfront-k) (global.get $qback-k))
)
(func $dequeue-k (export "dequeue-k") (result (ref null $cont))
(local $i i32)
(if (call $queue-empty-k)
(then (return (ref.null $cont)))
)
(local.set $i (global.get $qfront-k))
(global.set $qfront-k (i32.add (local.get $i) (i32.const 1)))
(table.get $queue (local.get $i))
)
(func $enqueue-k (export "enqueue-k") (param $k (ref $cont))
;; Check if queue is full
(if (i32.eq (global.get $qback-k) (table.size $queue))
(then
;; Check if there is enough space in the front to compact
(if (i32.lt_u (global.get $qfront-k) (global.get $qdelta))
(then
;; Space is below threshold, grow table instead
(drop (table.grow $queue (ref.null $cont) (global.get $qdelta)))
)
(else
;; Enough space, move entries up to head of table
(global.set $qback-k (i32.sub (global.get $qback-k) (global.get $qfront-k)))
(table.copy $queue $queue
(i32.const 0) ;; dest = new front = 0
(global.get $qfront-k) ;; src = old front
(global.get $qback-k) ;; len = new back = old back - old front
)
(table.fill $queue ;; null out old entries to avoid leaks
(global.get $qback-k) ;; start = new back
(ref.null $cont) ;; init value
(global.get $qfront-k) ;; len = old front = old front - new front
)
(global.set $qfront-k (i32.const 0))
)
)
)
)
(table.set $queue (global.get $qback-k) (local.get $k))
(global.set $qback-k (i32.add (global.get $qback-k) (i32.const 1)))
)
(global $qback-mb (mut i32) (i32.const 0))
(global $qfront-mb (mut i32) (i32.const 0))
(func $queue-empty-mb (export "queue-empty-mb") (result i32)
(i32.eq (global.get $qfront-mb) (global.get $qback-mb))
)
(func $dequeue-mb (export "dequeue-mb") (result i32)
(local $i i32)
(local $mb i32)
(if (call $queue-empty-mb)
(then (return (i32.const -1)))
)
(local.set $i (global.get $qfront-mb))
(global.set $qfront-mb (i32.add (local.get $i) (i32.const 1)))
(local.set $mb (i32.load (i32.mul (local.get $i) (i32.const 4))))
(return (local.get $mb))
)
(func $enqueue-mb (export "enqueue-mb") (param $mb i32)
;; Check if queue is full
(if (i32.eq (global.get $qback-mb) (i32.const 16383))
(then
;; Check if there is enough space in the front to compact
(if (i32.lt_u (global.get $qfront-mb) (global.get $qdelta))
(then
;; Space is below threshold, throw exception
(throw $too-many-mailboxes)
)
(else
;; Enough space, move entries up to head of table
(global.set $qback-mb (i32.sub (global.get $qback-mb) (global.get $qfront-mb)))
(memory.copy
(i32.const 0) ;; dest = new front = 0
(i32.mul (global.get $qfront-mb) (i32.const 4)) ;; src = old front
(i32.mul (global.get $qback-mb) (i32.const 4)) ;; len = new back = old back - old front
)
(memory.fill ;; null out old entries to avoid leaks
(i32.mul (global.get $qback-mb) (i32.const 4)) ;; start = new back
(i32.const -1) ;; init value
(i32.mul (global.get $qfront-mb) (i32.const 4)) ;; len = old front = old front - new front
)
(global.set $qfront-mb (i32.const 0))
)
)
)
)
(i32.store (i32.mul (global.get $qback-mb) (i32.const 4)) (local.get $mb))
(global.set $qback-mb (i32.add (global.get $qback-mb) (i32.const 1)))
)
)
(register "queue")
(module $mailboxes
;; Stupid implementation of mailboxes that raises an exception if
;; there are too many mailboxes or if more than one message is sent
;; to any given mailbox.
;;
;; Sufficient for the simple chain example.
;; -1 means empty
(func $log (import "spectest" "print_i32") (param i32))
(tag $too-many-mailboxes)
(tag $too-many-messages)
(memory 1)
(global $msize (mut i32) (i32.const 0)) ;; current number of mailboxes
(global $mmax i32 (i32.const 1024)) ;; maximum number of mailboxes
(func $init (export "init")
(global.set $msize (i32.const 0))
(memory.fill (i32.const 0) (i32.const -1) (i32.mul (global.get $mmax) (i32.const 4)))
)
(func $empty-mb (export "empty-mb") (param $mb i32) (result i32)
(local $offset i32)
(local.set $offset (i32.mul (local.get $mb) (i32.const 4)))
(i32.eq (i32.load (local.get $offset)) (i32.const -1))
)
(func $new-mb (export "new-mb") (result i32)
(local $mb i32)
(if (i32.ge_u (global.get $msize) (global.get $mmax))
(then (throw $too-many-mailboxes))
)
(local.set $mb (global.get $msize))
(global.set $msize (i32.add (global.get $msize) (i32.const 1)))
(return (local.get $mb))
)
(func $send-to-mb (export "send-to-mb") (param $v i32) (param $mb i32)
(local $offset i32)
(local.set $offset (i32.mul (local.get $mb) (i32.const 4)))
(if (call $empty-mb (local.get $mb))
(then (i32.store (local.get $offset) (local.get $v)))
(else (throw $too-many-messages))
)
)
(func $recv-from-mb (export "recv-from-mb") (param $mb i32) (result i32)
(local $v i32)
(local $offset i32)
(local.set $offset (i32.mul (local.get $mb) (i32.const 4)))
(local.set $v (i32.load (local.get $offset)))
(i32.store (local.get $offset) (i32.const -1))
(local.get $v)
)
)
(register "mailboxes")
;; actors implemented directly
(module $scheduler
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(func $log (import "spectest" "print_i32") (param i32))
(type $i-func (func (param i32))) ;; [i32] -> []
(type $i-cont (cont $i-func)) ;; cont ([i32] -> [])
(type $i-cont-func (func (param (ref $i-cont)))) ;; [(cont ([i32] -> []))] -> []
(type $i-cont-cont (cont $i-cont-func)) ;; cont ([(cont ([i32] -> []))] -> [])
;; mailbox interface
(func $init (import "mailboxes" "init"))
(func $empty-mb (import "mailboxes" "empty-mb") (param $mb i32) (result i32))
(func $new-mb (import "mailboxes" "new-mb") (result i32))
(func $send-to-mb (import "mailboxes" "send-to-mb") (param $v i32) (param $mb i32))
(func $recv-from-mb (import "mailboxes" "recv-from-mb") (param $mb i32) (result i32))
;; queue interface
(func $dequeue-mb (import "queue" "dequeue-mb") (result i32))
(func $enqueue-mb (import "queue" "enqueue-mb") (param i32))
(func $dequeue-k (import "queue" "dequeue-k") (result (ref null $cont)))
(func $enqueue-k (import "queue" "enqueue-k") (param (ref $cont)))
;; actor interface
;; self : [i32] -> []
;; spawn : [cont ([] -> [])] -> [i32]
;; send : [i32 i32] -> []
;; recv : [] -> [i32]
(tag $self (import "actor" "self") (result i32))
(tag $spawn (import "actor" "spawn") (param (ref $cont)) (result i32))
(tag $send (import "actor" "send") (param i32 i32))
(tag $recv (import "actor" "recv") (result i32))
(elem declare func $recv-againf)
;; We implement blocking by reinvoking recv with the original
;; handler. This is a common pattern nicely supported by shallow but
;; not deep handlers. However, it does require composing the new
;; reinvoked recv with the continuation. We simulate this behaviour
;; (inefficiently, perhaps) by resuming the continuation with an
;; identity handler and then building a new continuation. Might an
;; instruction for composing or extending continuations be palatable
;; / desirable?
;;
;; The resume_throw operation can be implemented (inefficiently)
;; with continuation composition.
;; compose recv with an existing continuation
(func $recv-againf (param $ik (ref $i-cont))
(local $res i32)
(suspend $recv)
(local.set $res)
(resume $i-cont (local.get $res) (local.get $ik))
)
(func $recv-again (param $ik (ref $i-cont)) (result (ref $cont))
(cont.bind $i-cont-cont $cont (local.get $ik) (cont.new $i-cont-cont (ref.func $recv-againf)))
)
;; There are multiple ways of avoiding the need for
;; $recv-again. Here are a couple.
;;
;; 1) Build handlers on top of lightweight threads (with fork and
;; yield). Then we can just keep on yielding until the mailbox is
;; non-empty, and delegate the actual scheduling to a separate
;; handler.
;;
;; 2) Distinguish between unblocked and blocked threads in the
;; thread queue. Typing makes this a bit of a pain to hack up
;; directly in Wasm, but in practice this is not difficult, and
;; similar to what existing actor implementations do.
(func $run (export "run") (param $nextk (ref null $cont))
(local $mine i32) ;; current mailbox
(local $ik (ref $i-cont))
(local $k (ref $cont))
(local $you (ref $cont))
(local $yours i32)
(call $init)
(local.set $mine (call $new-mb))
(loop $l
(if (ref.is_null (local.get $nextk)) (then (return)))
(block $on_self (result (ref $i-cont))
(block $on_spawn (result (ref $cont) (ref $i-cont))
(block $on_send (result i32 i32 (ref $cont))
(block $on_recv (result (ref $i-cont))
(resume $cont (on $self $on_self)
(on $spawn $on_spawn)
(on $send $on_send)
(on $recv $on_recv)
(local.get $nextk)
)
(local.set $mine (call $dequeue-mb))
(local.set $nextk (call $dequeue-k))
(br $l)
) ;; $on_recv (result (ref $i-cont))
(local.set $ik)
;; block this thread until the mailbox is non-empty
(if (call $empty-mb (local.get $mine))
(then (call $enqueue-mb (local.get $mine))
(call $enqueue-k (call $recv-again (local.get $ik)))
(local.set $mine (call $dequeue-mb))
(local.set $nextk (call $dequeue-k))
(br $l))
)
(local.set $nextk (cont.bind $i-cont $cont (call $recv-from-mb (local.get $mine)) (local.get $ik)))
(br $l)
) ;; $on_send (result i32 i32 (ref $cont))
(local.set $k)
(call $send-to-mb)
(local.set $nextk (local.get $k))
(br $l)
) ;; $on_spawn (result (ref $cont) (ref $i-cont))
(local.set $ik)
(local.set $you)
(call $new-mb)
(local.set $yours)
(call $enqueue-mb (local.get $yours))
(call $enqueue-k (local.get $you))
(local.set $nextk (cont.bind $i-cont $cont (local.get $yours) (local.get $ik)))
(br $l)
) ;; $on_self (result (ref $i-cont))
(local.set $ik)
(local.set $nextk (cont.bind $i-cont $cont (local.get $mine) (local.get $ik)))
(br $l)
)
)
)
(register "scheduler")
(module
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $i-func (func (param i32))) ;; [i32] -> []
(type $i-cont (cont $i-func)) ;; cont ([i32] -> [])
(func $log (import "spectest" "print_i32") (param i32))
(elem declare func $chain)
(func $act (import "scheduler" "run") (param $k (ref null $cont)))
(func $chain (import "chain" "chain") (param $n i32))
(func $run-chain (export "run-chain") (param $n i32)
(call $act (cont.bind $i-cont $cont (local.get $n) (cont.new $i-cont (ref.func $chain))))
)
)
(assert_return (invoke "run-chain" (i32.const 64)))