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(** semaphore, for limiting concurrency. *)
type t = { mutable n: int; max: int; mutex: Mutex.t; cond: Condition.t }
let create n =
if n <= 0 then invalid_arg "Semaphore.create";
{ n; max = n; mutex = Mutex.create (); cond = Condition.create () }
let acquire m t =
Mutex.lock t.mutex;
while t.n < m do
Condition.wait t.cond t.mutex
done;
assert (t.n >= m);
t.n <- t.n - m;
Condition.broadcast t.cond;
Mutex.unlock t.mutex
let release m t =
Mutex.lock t.mutex;
t.n <- t.n + m;
Condition.broadcast t.cond;
Mutex.unlock t.mutex
let num_acquired t = t.max - t.n