;; RUN: wast --assert default --snapshot tests/snapshots % -f stack-switching
;; dynamic lightweight threads via control/prompt
;; interface to control/prompt
(module $control
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $cont-func (func (param (ref $cont)))) ;; [cont ([] -> [])] -> []
(type $cont-cont (cont $cont-func)) ;; cont ([cont ([] -> [])] -> [])
;; Implementation of a generic delimited control operator using
;; effect handlers.
;;
;; For lightweight threads we have no payload. More general types
;; for control and prompt are:
;;
;; control : ([cont ([ta*] -> [tr*])] -> [tr*]) -> [ta*]
;; prompt : cont ([] -> [tr*]) -> [tr*]
;;
;; (We can also give more refined types if we want to support
;; answer-type modification and various flavours of answer-type
;; polymorphism - but these are well outside the scope of a Wasm
;; proposal!)
;;
;; (Technically this is control0/prompt0 rather than
;; control/prompt.)
(tag $control (export "control") (param (ref $cont-cont))) ;; control : ([cont ([] -> [])] -> []) -> []
(func $prompt (export "prompt") (param $nextk (ref null $cont)) ;; prompt : cont ([] -> []) -> []
(local $h (ref $cont-cont))
(local $k (ref $cont))
(block $on_control (result (ref $cont-cont) (ref $cont))
(resume $cont (on $control $on_control)
(local.get $nextk))
(return)
) ;; $on_control (param (ref $cont-func) (ref $cont))
(local.set $k)
(local.set $h)
(resume $cont-cont (local.get $k) (local.get $h))
)
)
(register "control")
;; With control/prompt we use functions for abstracting over yield and
;; fork operations rather than tags.
(module $example
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $cont-func (func (param (ref $cont)))) ;; [cont ([] -> [])] -> []
(type $cont-cont (cont $cont-func)) ;; cont ([cont ([] -> [])] -> [])
(type $func-cont-func-func (func (param (ref $func)) (param (ref $cont-func)))) ;; ([] -> []) -> ([cont ([] -> [])] -> []) -> []
(type $func-cont-func-cont (cont $func-cont-func-func)) ;; cont (([] -> []) -> ([cont ([] -> [])] -> []) -> [])
(func $log (import "spectest" "print_i32") (param i32))
(elem declare func $main $thread1 $thread2 $thread3)
(func $main (export "main") (param $yield (ref $func)) (param $fork (ref $cont-func))
(call $log (i32.const 0))
(call_ref $cont-func
(cont.bind $func-cont-func-cont $cont (local.get $yield) (local.get $fork)
(cont.new $func-cont-func-cont (ref.func $thread1)))
(local.get $fork))
(call $log (i32.const 1))
(call_ref $cont-func
(cont.bind $func-cont-func-cont $cont (local.get $yield) (local.get $fork)
(cont.new $func-cont-func-cont (ref.func $thread2)))
(local.get $fork))
(call $log (i32.const 2))
(call_ref $cont-func
(cont.bind $func-cont-func-cont $cont (local.get $yield) (local.get $fork)
(cont.new $func-cont-func-cont (ref.func $thread3)))
(local.get $fork))
(call $log (i32.const 3))
)
(func $thread1 (param $yield (ref $func)) (param $fork (ref $cont-func))
(call $log (i32.const 10))
(call_ref $func (local.get $yield))
(call $log (i32.const 11))
(call_ref $func (local.get $yield))
(call $log (i32.const 12))
)
(func $thread2 (param $yield (ref $func)) (param $fork (ref $cont-func))
(call $log (i32.const 20))
(call_ref $func (local.get $yield))
(call $log (i32.const 21))
(call_ref $func (local.get $yield))
(call $log (i32.const 22))
)
(func $thread3 (param $yield (ref $func)) (param $fork (ref $cont-func))
(call $log (i32.const 30))
(call_ref $func (local.get $yield))
(call $log (i32.const 31))
(call_ref $func (local.get $yield))
(call $log (i32.const 32))
)
)
(register "example")
(module $queue
(type $func (func))
(type $cont (cont $func))
(func $log (import "spectest" "print_i32") (param i32))
;; Table as simple queue (keeping it simple, no ring buffer)
(table $queue 0 (ref null $cont))
(global $qdelta i32 (i32.const 10))
(global $qback (mut i32) (i32.const 0))
(global $qfront (mut i32) (i32.const 0))
(func $queue-empty (export "queue-empty") (result i32)
(i32.eq (global.get $qfront) (global.get $qback))
)
(func $dequeue (export "dequeue") (result (ref null $cont))
(local $i i32)
(if (call $queue-empty)
(then (return (ref.null $cont)))
)
(local.set $i (global.get $qfront))
(global.set $qfront (i32.add (local.get $i) (i32.const 1)))
(table.get $queue (local.get $i))
)
(func $enqueue (export "enqueue") (param $k (ref $cont))
;; Check if queue is full
(if (i32.eq (global.get $qback) (table.size $queue))
(then
;; Check if there is enough space in the front to compact
(if (i32.lt_u (global.get $qfront) (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 (i32.sub (global.get $qback) (global.get $qfront)))
(table.copy $queue $queue
(i32.const 0) ;; dest = new front = 0
(global.get $qfront) ;; src = old front
(global.get $qback) ;; len = new back = old back - old front
)
(table.fill $queue ;; null out old entries to avoid leaks
(global.get $qback) ;; start = new back
(ref.null $cont) ;; init value
(global.get $qfront) ;; len = old front = old front - new front
)
(global.set $qfront (i32.const 0))
)
)
)
)
(table.set $queue (global.get $qback) (local.get $k))
(global.set $qback (i32.add (global.get $qback) (i32.const 1)))
)
)
(register "queue")
(module $scheduler
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $cont-func (func (param (ref $cont)))) ;; [cont ([] -> [])] -> []
(type $cont-cont (cont $cont-func)) ;; cont ([cont ([] -> [])] -> [])
(type $func-cont-func-func (func (param (ref $func)) (param (ref $cont-func)))) ;; ([] -> []) -> ([cont ([] -> [])] -> []) -> []
(type $func-cont-func-cont (cont $func-cont-func-func)) ;; cont (([] -> []) -> ([cont ([] -> [])] -> []) -> [])
(type $func-cont-cont (func (param (ref $cont)) (param (ref $cont))))
(type $cont-cont-func (cont $func-cont-cont))
(func $log (import "spectest" "print_i32") (param i32))
;; queue interface
(func $queue-empty (import "queue" "queue-empty") (result i32))
(func $dequeue (import "queue" "dequeue") (result (ref null $cont)))
(func $enqueue (import "queue" "enqueue") (param $k (ref $cont)))
(elem declare func
$handle-yield-sync $handle-yield
$handle-fork-sync $handle-fork-kt $handle-fork-tk $handle-fork-ykt $handle-fork-ytk
$yield
$fork-sync $fork-kt $fork-tk $fork-ykt $fork-ytk)
;; control/prompt interface
(tag $control (import "control" "control") (param (ref $cont-cont))) ;; control : ([cont ([] -> [])] -> []) -> []
(func $prompt (import "control" "prompt") (param $nextk (ref null $cont))) ;; prompt : cont ([] -> []) -> []
;; generic boilerplate scheduler
;;
;; with control/prompt the core scheduler loop must be decoupled
;; from the implementations of each operation (yield / fork) as the
;; latter are passed in as arguments to user code
(func $scheduler (param $nextk (ref null $cont))
(loop $loop
(if (ref.is_null (local.get $nextk)) (then (return)))
(call $prompt (local.get $nextk))
(local.set $nextk (call $dequeue))
(br $loop)
)
)
;; func.bind is needed in the implementations of fork
;;
;; More generally func.bind is needed for any operation that
;; takes arguments.
;;
;; One could use another continuation here instead, but constructing
;; a new continuation every time an operation is invoked seems
;; unnecessarily wasteful.
;; synchronous scheduler
(func $handle-yield-sync (param $k (ref $cont))
(call $scheduler (local.get $k))
)
(func $yield-sync
(suspend $control (cont.new $cont-cont (ref.func $handle-yield)))
)
(func $handle-fork-sync (param $t (ref $cont)) (param $k (ref $cont))
(call $enqueue (local.get $t))
(call $scheduler (local.get $k))
)
(func $fork-sync (param $t (ref $cont))
(suspend $control
(cont.bind $cont-cont-func $cont-cont (local.get $t)
(cont.new $cont-cont-func (ref.func $handle-fork-sync))))
)
(func $sync (export "sync") (param $k (ref $func-cont-func-cont))
(call $scheduler
(cont.bind $func-cont-func-cont $cont (ref.func $yield) (ref.func $fork-sync) (local.get $k)))
)
;; asynchronous yield (used by all asynchronous schedulers)
(func $handle-yield (param $k (ref $cont))
(call $enqueue (local.get $k))
(call $scheduler (call $dequeue))
)
(func $yield
(suspend $control (cont.new $cont-cont (ref.func $handle-yield)))
)
;; four asynchronous implementations of fork:
;; * kt and tk don't yield on encountering a fork
;; 1) kt runs the continuation, queuing up the new thread for later
;; 2) tk runs the new thread first, queuing up the continuation for later
;; * ykt and ytk do yield on encountering a fork
;; 3) ykt runs the continuation, queuing up the new thread for later
;; 4) ytk runs the new thread first, queuing up the continuation for later
;; no yield on fork, continuation first
(func $handle-fork-kt (param $t (ref $cont)) (param $k (ref $cont))
(call $enqueue (local.get $t))
(call $scheduler (local.get $k))
)
(func $fork-kt (param $t (ref $cont))
(suspend $control
(cont.bind $cont-cont-func $cont-cont (local.get $t)
(cont.new $cont-cont-func (ref.func $handle-fork-kt))))
)
(func $kt (export "kt") (param $k (ref $func-cont-func-cont))
(call $scheduler
(cont.bind $func-cont-func-cont $cont (ref.func $yield) (ref.func $fork-kt) (local.get $k)))
)
;; no yield on fork, new thread first
(func $handle-fork-tk (param $t (ref $cont)) (param $k (ref $cont))
(call $enqueue (local.get $k))
(call $scheduler (local.get $t))
)
(func $fork-tk (param $t (ref $cont))
(suspend $control
(cont.bind $cont-cont-func $cont-cont (local.get $t)
(cont.new $cont-cont-func (ref.func $handle-fork-tk))))
)
(func $tk (export "tk") (param $k (ref $func-cont-func-cont))
(call $scheduler
(cont.bind $func-cont-func-cont $cont (ref.func $yield) (ref.func $fork-tk) (local.get $k)))
)
;; yield on fork, continuation first
(func $handle-fork-ykt (param $t (ref $cont)) (param $k (ref $cont))
(call $enqueue (local.get $k))
(call $enqueue (local.get $t))
(call $scheduler (call $dequeue))
)
(func $fork-ykt (param $t (ref $cont))
(suspend $control
(cont.bind $cont-cont-func $cont-cont (local.get $t)
(cont.new $cont-cont-func (ref.func $handle-fork-ykt))))
)
(func $ykt (export "ykt") (param $k (ref $func-cont-func-cont))
(call $scheduler
(cont.bind $func-cont-func-cont $cont (ref.func $yield) (ref.func $fork-ykt) (local.get $k)))
)
;; yield on fork, new thread first
(func $handle-fork-ytk (param $t (ref $cont)) (param $k (ref $cont))
(call $enqueue (local.get $t))
(call $enqueue (local.get $k))
(call $scheduler (call $dequeue))
)
(func $fork-ytk (param $t (ref $cont))
(suspend $control
(cont.bind $cont-cont-func $cont-cont (local.get $t)
(cont.new $cont-cont-func (ref.func $handle-fork-ytk))))
)
(func $ytk (export "ytk") (param $k (ref $func-cont-func-cont))
(call $scheduler
(cont.bind $func-cont-func-cont $cont (ref.func $yield) (ref.func $fork-ytk) (local.get $k)))
)
)
(register "scheduler")
(module
(type $func (func)) ;; [] -> []
(type $cont (cont $func)) ;; cont ([] -> [])
(type $cont-func (func (param (ref $cont)))) ;; [cont ([] -> [])] -> []
(type $cont-cont (cont $cont-func)) ;; cont ([cont ([] -> [])] -> [])
(type $func-cont-func-func (func (param (ref $func)) (param (ref $cont-func)))) ;; ([] -> []) -> ([cont ([] -> [])] -> []) -> []
(type $func-cont-func-cont (cont $func-cont-func-func)) ;; cont (([] -> []) -> ([cont ([] -> [])] -> []) -> [])
(func $scheduler-sync (import "scheduler" "sync") (param $nextk (ref $func-cont-func-cont)))
(func $scheduler-kt (import "scheduler" "kt") (param $nextk (ref $func-cont-func-cont)))
(func $scheduler-tk (import "scheduler" "tk") (param $nextk (ref $func-cont-func-cont)))
(func $scheduler-ykt (import "scheduler" "ykt") (param $nextk (ref $func-cont-func-cont)))
(func $scheduler-ytk (import "scheduler" "ytk") (param $nextk (ref $func-cont-func-cont)))
(func $log (import "spectest" "print_i32") (param i32))
(func $main (import "example" "main") (param $yield (ref $func)) (param $fork (ref $cont-func)))
(elem declare func $main)
(func $run (export "run")
(call $log (i32.const -1))
(call $scheduler-sync (cont.new $func-cont-func-cont (ref.func $main)))
(call $log (i32.const -2))
(call $scheduler-kt (cont.new $func-cont-func-cont (ref.func $main)))
(call $log (i32.const -3))
(call $scheduler-tk (cont.new $func-cont-func-cont (ref.func $main)))
(call $log (i32.const -4))
(call $scheduler-ykt (cont.new $func-cont-func-cont (ref.func $main)))
(call $log (i32.const -5))
(call $scheduler-ytk (cont.new $func-cont-func-cont (ref.func $main)))
(call $log (i32.const -6))
)
)
(invoke "run")