cooperative-scheduling.js

/**
 * @license
 * MIT License
 *
 * Copyright (c) 2020 Alexis Munsayac
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 *
 * @author Alexis Munsayac <alexis.munsayac@gmail.com>
 * @copyright Alexis Munsayac 2020
 */

/**
 * A promise with controllable fulfillment
 */
function deferred() {
  const obj = {};
  obj.promise = new Promise((res, rej) => {
    obj.resolve = res;
    obj.reject = rej;
  });
  return obj;
}

function runThreads(...threads) {
  const suspend = [];
  const finished = [];

  function runThread(index = 0) {
    if (index >= 0 && index < threads.length) {
      if (finished[index]) {
        runThread(index + 1);
      } else if (suspend[index]) {
        suspend[index].resolve();
      } else {
        threads[index](
          () => {
            suspend[index] = deferred();
            runThread(index + 1);
            return suspend[index].promise;
          },
          () => {
            suspend[index] = deferred();
            runThread(index - 1);
            return suspend[index].promise;
          },
        ).then(() => {
          finished[index] = true;
          runThread(index + 1);
        });
      }
    }
  }

  runThread();
}


async function A(next, prev) {
  console.log('BEGIN A');
  console.log('sending: A -> B -- C');
  await next();
  console.log('received: A <- B -- C');
  console.log('sending: A -> B -- C');
  console.log('END A');
}

async function B(next, prev) {
  console.log('BEGIN B');
  console.log('received: A -> B -- C');
  console.log('sending: A <- B -- C');
  await prev();
  console.log('received: A -> B -- C');
  console.log('sending: A -- B -> C');
  await next();
  console.log('received: A -- B <- C');
  console.log('sending: A -- B -> C');
  console.log('END B');
}

async function C(next, prev) {
  console.log('BEGIN C');
  console.log('received: A -- B -> C');
  console.log('sending: A -- B <- C');
  await prev();
  console.log('received: A -- B -> C');
  console.log('END C');
}

runThreads(A, B, C);