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(.module:
[lux #*
[abstract
[monad (#+ do)]]
[control
["." io (#+ IO)]
["." try (#+ Try)]
["." exception (#+ exception:)]]
[data
[text
["%" format (#+ format)]]
[number
["n" nat]
["i" int]]
[collection
["." queue (#+ Queue)]]]
[type
abstract
["." refinement]]
["." macro]]
[//
["." atom (#+ Atom)]
["." promise (#+ Promise Resolver)]])
(type: State
{#max-positions Nat
#open-positions Int
#waiting-list (Queue (Resolver Any))})
(abstract: #export Semaphore
{#.doc "A tool for controlling access to resources by multiple concurrent processes."}
(Atom State)
(def: most-positions-possible
(.nat (:: i.interval top)))
(def: #export (semaphore initial-open-positions)
(-> Nat Semaphore)
(let [max-positions (n.min initial-open-positions
..most-positions-possible)]
(:abstraction (atom.atom {#max-positions max-positions
#open-positions (.int max-positions)
#waiting-list queue.empty}))))
(def: #export (wait semaphore)
(Ex [k] (-> Semaphore (Promise Any)))
(let [semaphore (:representation semaphore)
[signal sink] (: [(Promise Any) (Resolver Any)]
(promise.promise []))]
(exec (promise.future
(loop [_ []]
(do io.monad
[state (atom.read semaphore)
#let [[ready? state'] (: [Bit State]
(if (i.> +0 (get@ #open-positions state))
[true (|> state
(update@ #open-positions dec))]
[false (|> state
(update@ #open-positions dec)
(update@ #waiting-list (queue.push sink)))]))]
success? (atom.compare-and-swap state state' semaphore)]
(if success?
(if ready?
(sink [])
(wrap false))
(recur [])))))
signal)))
(exception: #export (semaphore-is-maxed-out {max-positions Nat})
(exception.report
["Max Positions" (%.nat max-positions)]))
(def: #export (signal semaphore)
(Ex [k] (-> Semaphore (Promise (Try Int))))
(let [semaphore (:representation semaphore)]
(promise.future
(loop [_ []]
(do {@ io.monad}
[state (atom.read semaphore)
#let [[?sink state' maxed-out?] (: [(Maybe (Resolver Any)) State Bit]
(case (queue.peek (get@ #waiting-list state))
#.None
(if (n.= (get@ #max-positions state)
(.nat (get@ #open-positions state)))
[#.None
state
true]
[#.None
(update@ #open-positions inc state)
false])
(#.Some head)
[(#.Some head)
(|> state
(update@ #open-positions inc)
(update@ #waiting-list queue.pop))
false]))]]
(if maxed-out?
(wrap (exception.throw ..semaphore-is-maxed-out [(get@ #max-positions state)]))
(do @
[#let [open-positions (get@ #open-positions state')]
success? (atom.compare-and-swap state state' semaphore)]
(if success?
(do @
[_ (case ?sink
#.None
(wrap true)
(#.Some sink)
(sink []))]
(wrap (#try.Success open-positions)))
(recur [])))))))))
)
(abstract: #export Mutex
{#.doc "A mutual-exclusion lock that can only be acquired by one process at a time."}
Semaphore
(def: #export (mutex _)
(-> Any Mutex)
(:abstraction (semaphore 1)))
(def: acquire
(-> Mutex (Promise Any))
(|>> :representation wait))
(def: release
(-> Mutex (Promise Any))
(|>> :representation signal))
(def: #export (synchronize mutex procedure)
(All [a] (-> Mutex (IO (Promise a)) (Promise a)))
(do promise.monad
[_ (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 Any))
(loop [step 0]
(if (n.< times step)
(do promise.monad
[_ (..signal turnstile)]
(recur (inc step)))
(:: promise.monad wrap []))))
(template [<phase> <update> <goal> <turnstile>]
[(def: (<phase> (^:representation barrier))
(-> Barrier (Promise Any))
(do promise.monad
[#let [limit (refinement.un-refine (get@ #limit barrier))
goal <goal>
count (io.run (atom.update <update> (get@ #count barrier)))
reached? (n.= goal count)]]
(if reached?
(un-block limit (get@ <turnstile> barrier))
(wait (get@ <turnstile> barrier)))))]
[start inc limit #start-turnstile]
[end dec 0 #end-turnstile]
)
(def: #export (block barrier)
(-> Barrier (Promise Any))
(do promise.monad
[_ (..start barrier)]
(..end barrier)))
)
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