Threads Scratch for Unison

threads-scratch.u

use .base
use .base.Text
use .base.Nat

counter.doc = [: 
    @counter takes an `id` parameter and number `n` parameter to be incremented.
    Prints id and number: "Counter <id>: <n>".
    Recursively calls itself every 3 seconds with an incremented number. 

    @[signature] counter
:]
counter: Nat -> Nat -> ()
counter id n = 
    delay (3 * 1000 * 1000) -- ~3 sec
    printLine ("Counter " ++ (toText id) ++ ": " ++ (toText n))
    counter id (n+1)

forkCounters: Nat -> [ThreadId] -> [ThreadId]
forkCounters num acc = 
    if num < 1 then acc 
    else 
        tid = fork '(counter num 0)
        printLine ("New Counter Thread -- " ++ (match tid with ThreadId t -> t))
        forkCounters (drop num 1) (acc List.++ [tid])

release: [ThreadId] -> ()
release threadIds = 
    match (List.head threadIds) with Some tid ->
        kill tid
        printLine ("Stopped thread -- " ++ (match tid with ThreadId t -> t))
        match (List.tail threadIds) with 
            Some ts -> release ts

what: [ThreadId] -> ()
what threadIds =
    printLine ("What received " ++ (toText (List.size threadIds)) ++ " thread ids!")
    printLine ("What waiting for input...")
    -- Just block on any input...
    cmd = !readLine
    printLine cmd

main : '{io.IO} ()
main = 'let
    acquire = '(forkCounters 2 [])
    bracket acquire release what
    printLine "Done"