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(.module:
lux
(lux (control [monad #+ do])
(concurrency [atom #+ Atom]
[promise #+ Promise])
[io #+ IO]
(type abstract
[refinement])))
(type: State
{#open-positions Nat
#waiting-list (List (Promise Unit))})
(abstract: #export Semaphore
{#.doc "A tool for controlling access to resources by multiple concurrent processes."}
(Atom State)
(def: #export (semaphore init-open-positions)
(-> Nat Semaphore)
(@abstraction (atom.atom {#open-positions init-open-positions
#waiting-list (list)})))
(def: #export (wait semaphore)
(Ex [k] (-> Semaphore (Promise Unit)))
(let [semaphore (@representation semaphore)]
(io.run
(loop [signal (: (Promise Unit)
(promise.promise #.None))]
(do io.Monad<IO>
[state (atom.read semaphore)
#let [[ready? state'] (: [Bool State]
(case (get@ #open-positions state)
+0 [false (update@ #waiting-list (|>> (#.Cons signal))
state)]
_ [true (update@ #open-positions n/dec
state)]))]
success? (atom.compare-and-swap state state' semaphore)
_ (if ready?
(promise.resolve [] signal)
(wrap false))]
(if success?
(wrap signal)
(recur signal)))))))
(def: #export (signal semaphore)
(Ex [k] (-> Semaphore (Promise Unit)))
(let [semaphore (@representation semaphore)]
(promise.future
(loop [_ []]
(do io.Monad<IO>
[state (atom.read semaphore)
#let [[?signal state'] (: [(Maybe (Promise Unit)) State]
(case (get@ #waiting-list state)
#.Nil
[#.None (update@ #open-positions n/inc state)]
(#.Cons head tail)
[(#.Some head) (set@ #waiting-list tail state)]))]
success? (atom.compare-and-swap state state' semaphore)]
(if success?
(do @
[_ (case ?signal
#.None
(wrap true)
(#.Some signal)
(promise.resolve [] signal))]
(wrap []))
(recur [])))))))
)
(abstract: #export Mutex
{#.doc "A mutual-exclusion lock that can only be acquired by one process at a time."}
Semaphore
(def: #export (mutex _)
(-> Top Mutex)
(@abstraction (semaphore +1)))
(def: (acquire mutex)
(-> Mutex (Promise Unit))
(wait (@representation mutex)))
(def: (release mutex)
(-> Mutex (Promise Unit))
(signal (@representation mutex)))
(def: #export (synchronize mutex procedure)
(All [a] (-> Mutex (IO (Promise a)) (Promise a)))
(do promise.Monad<Promise>
[_ (acquire mutex)
output (io.run procedure)
_ (release mutex)]
(wrap output)))
)
(def: #export limit (refinement.refinement (n/> +0)))
(type: #export Limit (~ (refinement.type limit)))
(abstract: #export Barrier
{#.doc "A barrier that blocks all processes from proceeding until a given number of processes are parked at the barrier."}
{#limit Limit
#count (Atom Nat)
#start-turnstile Semaphore
#end-turnstile Semaphore}
(def: #export (barrier limit)
(-> Limit Barrier)
(@abstraction {#limit limit
#count (atom.atom +0)
#start-turnstile (semaphore +0)
#end-turnstile (semaphore +0)}))
(def: (un-block times turnstile)
(-> Nat Semaphore (Promise Top))
(loop [step +0]
(if (n/< times step)
(do promise.Monad<Promise>
[_ (signal turnstile)]
(recur (n/inc step)))
(:: promise.Monad<Promise> wrap []))))
(do-template [<phase> <update> <goal> <turnstile>]
[(def: (<phase> (^@representation barrier))
(-> Barrier (Promise Unit))
(do promise.Monad<Promise>
[#let [limit (refinement.un-refine (get@ #limit barrier))
goal <goal>
count (io.run (atom.update <update> (get@ #count barrier)))]
_ (if (n/= goal count)
(un-block limit (get@ <turnstile> barrier))
(wrap []))]
(wait (get@ <turnstile> barrier))))]
[start n/inc limit #start-turnstile]
[end n/dec +0 #end-turnstile]
)
(def: #export (block barrier)
(-> Barrier (Promise Unit))
(do promise.Monad<Promise>
[_ (start barrier)]
(end barrier)))
)
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