latch.ts

import { test, runIfMain } from "https://deno.land/std/testing/mod.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

export class Latch<T> {
  // Array of `[resolve_function, value]` tuples.
  send_queue: Array<[() => void, T]> = []
  // Array of `resolve_function` values.
  recv_queue: Array<(value: T) => void> = []
  
  send(value: T): Promise<void> {
    const recv_resolve = this.recv_queue.shift();
    if (recv_resolve) {
      recv_resolve(value);
      return Promise.resolve();
    } else {
      return new Promise((res, _) => this.send_queue.push([res, value]));
    }
  }

  recv(): Promise<T> {
    const s = this.send_queue.shift();
    if (s) {
      const [send_resolve, value] = s;
      send_resolve();
      return Promise.resolve(value);
    } else {
      return new Promise((res, _) => this.recv_queue.push(res));
    }
  }
}

async function send3(latch: Latch<number>): Promise<void> {
  await latch.send(1);
  await latch.send(2);
  await latch.send(3);
}

test(async function asyncLatch(): Promise<void> {
  const latch = new Latch<number>();
  send3(latch);

  assertEquals(1, await latch.recv());
  assertEquals(2, await latch.recv());
  assertEquals(3, await latch.recv());
  let _lastPromise = latch.recv();
});

runIfMain(import.meta)