-- demo\rosetta\checkpoint_synchronisation.exw
constant NPARTS = 3
integer workers = 0
sequence waiters = {}
bool terminate = false

procedure checkpoint(integer task_id)
    if length(waiters)+1=NPARTS or terminate then
        printf(1,"checkpoint\n")
        for i=1 to length(waiters) do
            task_schedule(waiters[i],1)
        end for
        waiters = {}
    else
        waiters &= task_id
        task_suspend(task_id)
        task_yield()
    end if
end procedure

procedure worker(string name)
    printf(1,"worker %s running\n",{name})
    while not terminate do
        printf(1,"worker %s begins part\n",{name})
        task_delay(rnd())
        printf(1,"worker %s completes part\n",{name})
        checkpoint(task_self())
        if rnd()>0.95 then exit end if
        task_delay(rnd())
    end while
    printf(1,"worker %s leaves\n",{name})
    workers -= 1
end procedure

string name = "A"

while get_key()!=#1B do -- (key escape to shut down)
    if workers<NPARTS then
        integer task_id = task_create(routine_id("worker"),{name})
        task_schedule(task_id,1)
        name[1] += 1
        workers += 1
    end if
    task_yield()
end while
printf(1,"escape keyed\n")
terminate = true
while workers>0 do
    task_yield()
end while