firefox/devtools/shared/worker/worker.sys.mjs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

let MESSAGE_COUNTER = 0;

function dumpn(_msg) {
  // dump(msg + "\n");
}

/**
 * Creates a wrapper around a ChromeWorker, providing easy
 * communication to offload demanding tasks. The corresponding URL
 * must implement the interface provided by `devtools/shared/worker/helper`.
 *
 * @param {string} url
 *        The URL of the worker.
 * @param Object opts
 *        An option with the following optional fields:
 *        - name: a name that will be printed with logs
 *        - verbose: log incoming and outgoing messages
 */
export function DevToolsWorker(url, opts) {
  opts = opts || {};
  this._worker = new ChromeWorker(url);
  this._verbose = opts.verbose;
  this._name = opts.name;

  this._worker.addEventListener("error", this.onError);
}

/**
 * Performs the given task in a chrome worker, passing in data.
 * Returns a promise that resolves when the task is completed, resulting in
 * the return value of the task.
 *
 * @param {string} task
 *        The name of the task to execute in the worker.
 * @param {any} data
 *        Data to be passed into the task implemented by the worker.
 * @param {undefined|Array} transfer
 *        Optional array of transferable objects to transfer ownership of.
 * @return {Promise}
 */
DevToolsWorker.prototype.performTask = function (task, data, transfer) {
  if (this._destroyed) {
    return Promise.reject(
      "Cannot call performTask on a destroyed DevToolsWorker"
    );
  }
  const worker = this._worker;
  const id = ++MESSAGE_COUNTER;
  const payload = { task, id, data };

  if (this._verbose && dumpn) {
    dumpn(
      "Sending message to worker" +
        (this._name ? " (" + this._name + ")" : "") +
        ": " +
        JSON.stringify(payload, null, 2)
    );
  }
  worker.postMessage(payload, transfer);

  return new Promise((resolve, reject) => {
    const listener = ({ data: result }) => {
      if (this._verbose && dumpn) {
        dumpn(
          "Received message from worker" +
            (this._name ? " (" + this._name + ")" : "") +
            ": " +
            JSON.stringify(result, null, 2)
        );
      }

      if (result.id !== id) {
        return;
      }
      worker.removeEventListener("message", listener);
      if (result.error) {
        reject(result.error);
      } else {
        resolve(result.response);
      }
    };

    worker.addEventListener("message", listener);
  });
};

/**
 * Terminates the underlying worker. Use when no longer needing the worker.
 */
DevToolsWorker.prototype.destroy = function () {
  this._worker.terminate();
  this._worker = null;
  this._destroyed = true;
};

DevToolsWorker.prototype.onError = function ({ message, filename, lineno }) {
  dump(new Error(message + " @ " + filename + ":" + lineno) + "\n");
};

/**
 * Takes a function and returns a Worker-wrapped version of the same function.
 * Returns a promise upon resolution.
 * @see `./devtools/shared/shared/tests/browser/browser_devtools-worker-03.js
 *
 * ⚠ This should only be used for tests or A/B testing performance ⚠
 *
 * The original function must:
 *
 * Be a pure function, that is, not use any variables not declared within the
 * function, or its arguments.
 *
 * Return a value or a promise.
 *
 * Note any state change in the worker will not affect the callee's context.
 *
 * @param {function} fn
 * @return {function}
 */
export function workerify(fn) {
  console.warn(
    "`workerify` should only be used in tests or measuring performance. " +
      "This creates an object URL on the browser window, and should not be " +
      "used in production."
  );
  // Fetch modules here as we don't want to include it normally.
  // eslint-disable-next-line no-shadow
  const { URL, Blob } = Services.wm.getMostRecentWindow("navigator:browser");
  const stringifiedFn = createWorkerString(fn);
  const blob = new Blob([stringifiedFn]);
  const url = URL.createObjectURL(blob);
  const worker = new DevToolsWorker(url);

  const wrapperFn = (data, transfer) =>
    worker.performTask("workerifiedTask", data, transfer);

  wrapperFn.destroy = function () {
    URL.revokeObjectURL(url);
    worker.destroy();
  };

  return wrapperFn;
}

/**
 * Takes a function, and stringifies it, attaching the worker-helper.js
 * boilerplate hooks.
 */
function createWorkerString(fn) {
  return `importScripts("resource://gre/modules/workers/require.js");
          const { createTask } = require("resource://devtools/shared/worker/helper.js");
          createTask(self, "workerifiedTask", ${fn.toString()});`;
}