7 files changed, 614 insertions, 0 deletions
diff --git a/devtools/shared/worker/helper.js b/devtools/shared/worker/helper.js
new file mode 100644
index 0000000000..20ccd3de5e
--- /dev/null
+++ b/devtools/shared/worker/helper.js
@@ -0,0 +1,138 @@
+/* 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/. */
+
+/* eslint-env amd */
+
+"use strict";
+
+/* global workerHelper */
+/* exported workerHelper */
+(function (root, factory) {
+  if (typeof define === "function" && define.amd) {
+    define(factory);
+  } else if (typeof exports === "object") {
+    module.exports = factory();
+  } else {
+    root.workerHelper = factory();
+  }
+})(this, function () {
+  /**
+   * This file is to only be included by ChromeWorkers. This exposes
+   * a `createTask` function to workers to register tasks for communication
+   * back to `devtools/shared/worker`.
+   *
+   * Tasks can be send their responses via a return value, either a primitive
+   * or a promise.
+   *
+   * createTask(self, "average", function (data) {
+   *   return data.reduce((sum, val) => sum + val, 0) / data.length;
+   * });
+   *
+   * createTask(self, "average", function (data) {
+   *   return new Promise((resolve, reject) => {
+   *     resolve(data.reduce((sum, val) => sum + val, 0) / data.length);
+   *   });
+   * });
+   *
+   *
+   * Errors:
+   *
+   * Returning an Error value, or if the returned promise is rejected, this
+   * propagates to the DevToolsWorker as a rejected promise. If an error is
+   * thrown in a synchronous function, that error is also propagated.
+   */
+
+  /**
+   * Takes a worker's `self` object, a task name, and a function to
+   * be called when that task is called. The task is called with the
+   * passed in data as the first argument
+   *
+   * @param {object} self
+   * @param {string} name
+   * @param {function} fn
+   */
+  function createTask(self, name, fn) {
+    // Store a hash of task name to function on the Worker
+    if (!self._tasks) {
+      self._tasks = {};
+    }
+
+    // Create the onmessage handler if not yet created.
+    if (!self.onmessage) {
+      self.onmessage = createHandler(self);
+    }
+
+    // Store the task on the worker.
+    self._tasks[name] = fn;
+  }
+
+  /**
+   * Creates the `self.onmessage` handler for a Worker.
+   *
+   * @param {object} self
+   * @return {function}
+   */
+  function createHandler(self) {
+    return function (e) {
+      const { id, task, data } = e.data;
+      const taskFn = self._tasks[task];
+
+      if (!taskFn) {
+        self.postMessage({ id, error: `Task "${task}" not found in worker.` });
+        return;
+      }
+
+      try {
+        handleResponse(taskFn(data));
+      } catch (ex) {
+        handleError(ex);
+      }
+
+      function handleResponse(response) {
+        // If a promise
+        if (response && typeof response.then === "function") {
+          response.then(
+            val => self.postMessage({ id, response: val }),
+            handleError
+          );
+        } else if (response instanceof Error) {
+          // If an error object
+          handleError(response);
+        } else {
+          // If anything else
+          self.postMessage({ id, response });
+        }
+      }
+
+      function handleError(error = "Error") {
+        try {
+          // First, try and structured clone the error across directly.
+          self.postMessage({ id, error });
+        } catch (x) {
+          // We could not clone whatever error value was given. Do our best to
+          // stringify it.
+          let errorString = `Error while performing task "${task}": `;
+
+          try {
+            errorString += error.toString();
+          } catch (ex) {
+            errorString += "<could not stringify error>";
+          }
+
+          if ("stack" in error) {
+            try {
+              errorString += "\n" + error.stack;
+            } catch (err) {
+              // Do nothing
+            }
+          }
+
+          self.postMessage({ id, error: errorString });
+        }
+      }
+    };
+  }
+
+  return { createTask };
+});
diff --git a/devtools/shared/worker/moz.build b/devtools/shared/worker/moz.build
new file mode 100644
index 0000000000..432b740a85
--- /dev/null
+++ b/devtools/shared/worker/moz.build
@@ -0,0 +1,13 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+if CONFIG["MOZ_BUILD_APP"] != "mobile/android":
+    BROWSER_CHROME_MANIFESTS += ["tests/browser/browser.ini"]
+
+DevToolsModules(
+    "helper.js",
+    "worker.js",
+)
diff --git a/devtools/shared/worker/tests/browser/browser.ini b/devtools/shared/worker/tests/browser/browser.ini
new file mode 100644
index 0000000000..a64916dfff
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser.ini
@@ -0,0 +1,9 @@
+[DEFAULT]
+tags = devtools
+subsuite = devtools
+support-files =
+  ../../../../server/tests/browser/head.js
+
+[browser_worker-01.js]
+[browser_worker-02.js]
+[browser_worker-03.js]
diff --git a/devtools/shared/worker/tests/browser/browser_worker-01.js b/devtools/shared/worker/tests/browser/browser_worker-01.js
new file mode 100644
index 0000000000..a8dafcf4cb
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-01.js
@@ -0,0 +1,110 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the devtools/shared/worker communicates properly
+// as both CommonJS module and as a JSM.
+
+const BUFFER_SIZE = 8;
+
+registerCleanupFunction(function () {
+  Services.prefs.clearUserPref("security.allow_parent_unrestricted_js_loads");
+});
+
+add_task(async function () {
+  // Test both CJS and JSM versions
+
+  await testWorker("JSM", () =>
+    ChromeUtils.import("resource://devtools/shared/worker/worker.js")
+  );
+  await testWorker("CommonJS", () =>
+    require("resource://devtools/shared/worker/worker.js")
+  );
+  await testTransfer();
+});
+
+async function testWorker(context, workerFactory) {
+  // Needed for blob:null
+  Services.prefs.setBoolPref(
+    "security.allow_parent_unrestricted_js_loads",
+    true
+  );
+  const { DevToolsWorker, workerify } = workerFactory();
+
+  const blob = new Blob(
+    [
+      `
+importScripts("resource://gre/modules/workers/require.js");
+const { createTask } = require("resource://devtools/shared/worker/helper.js");
+
+createTask(self, "groupByField", function({
+  items,
+  groupField
+}) {
+  const groups = {};
+  for (const item of items) {
+    if (!groups[item[groupField]]) {
+      groups[item[groupField]] = [];
+    }
+    groups[item[groupField]].push(item);
+  }
+  return { groups };
+});
+    `,
+    ],
+    { type: "application/javascript" }
+  );
+
+  const WORKER_URL = URL.createObjectURL(blob);
+  const worker = new DevToolsWorker(WORKER_URL);
+
+  const results = await worker.performTask("groupByField", {
+    items: [
+      { name: "Paris", country: "France" },
+      { name: "Lagos", country: "Nigeria" },
+      { name: "Lyon", country: "France" },
+    ],
+    groupField: "country",
+  });
+
+  is(
+    Object.keys(results.groups).join(","),
+    "France,Nigeria",
+    `worker should have returned the expected result in ${context}`
+  );
+
+  URL.revokeObjectURL(WORKER_URL);
+
+  const fn = workerify(x => x * x);
+  is(await fn(5), 25, `workerify works in ${context}`);
+  fn.destroy();
+
+  worker.destroy();
+}
+
+async function testTransfer() {
+  Services.prefs.setBoolPref(
+    "security.allow_parent_unrestricted_js_loads",
+    true
+  );
+  const { workerify } = ChromeUtils.import(
+    "resource://devtools/shared/worker/worker.js"
+  );
+  const workerFn = workerify(({ buf }) => buf.byteLength);
+  const buf = new ArrayBuffer(BUFFER_SIZE);
+
+  is(
+    buf.byteLength,
+    BUFFER_SIZE,
+    "Size of the buffer before transfer is correct."
+  );
+
+  is(await workerFn({ buf }), 8, "Sent array buffer to worker");
+  is(buf.byteLength, 8, "Array buffer was copied, not transferred.");
+
+  is(await workerFn({ buf }, [buf]), 8, "Sent array buffer to worker");
+  is(buf.byteLength, 0, "Array buffer was transferred, not copied.");
+
+  workerFn.destroy();
+}
diff --git a/devtools/shared/worker/tests/browser/browser_worker-02.js b/devtools/shared/worker/tests/browser/browser_worker-02.js
new file mode 100644
index 0000000000..80c50cf887
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-02.js
@@ -0,0 +1,83 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests errors are handled properly by the DevToolsWorker.
+
+const {
+  DevToolsWorker,
+} = require("resource://devtools/shared/worker/worker.js");
+
+const blob = new Blob(
+  [
+    `
+importScripts("resource://gre/modules/workers/require.js");
+const { createTask } = require("resource://devtools/shared/worker/helper.js");
+
+createTask(self, "myTask", function({
+  shouldThrow,
+} = {}) {
+  if (shouldThrow) {
+    throw new Error("err");
+  }
+
+  return "OK";
+});
+    `,
+  ],
+  { type: "application/javascript" }
+);
+
+add_task(async function () {
+  try {
+    new DevToolsWorker("resource://i/dont/exist.js");
+    ok(false, "Creating a DevToolsWorker with an invalid URL throws");
+  } catch (e) {
+    ok(true, "Creating a DevToolsWorker with an invalid URL throws");
+  }
+
+  const WORKER_URL = URL.createObjectURL(blob);
+  const worker = new DevToolsWorker(WORKER_URL);
+  try {
+    await worker.performTask("myTask", { shouldThrow: true });
+    ok(
+      false,
+      "DevToolsWorker returns a rejected promise when an error occurs in the worker"
+    );
+  } catch (e) {
+    ok(
+      true,
+      "DevToolsWorker returns a rejected promise when an error occurs in the worker"
+    );
+  }
+
+  try {
+    await worker.performTask("not a real task");
+    ok(
+      false,
+      "DevToolsWorker returns a rejected promise when task does not exist"
+    );
+  } catch (e) {
+    ok(
+      true,
+      "DevToolsWorker returns a rejected promise when task does not exist"
+    );
+  }
+
+  worker.destroy();
+  try {
+    await worker.performTask("myTask");
+    ok(
+      false,
+      "DevToolsWorker rejects when performing a task on a destroyed worker"
+    );
+  } catch (e) {
+    ok(
+      true,
+      "DevToolsWorker rejects when performing a task on a destroyed worker"
+    );
+  }
+
+  URL.revokeObjectURL(WORKER_URL);
+});
diff --git a/devtools/shared/worker/tests/browser/browser_worker-03.js b/devtools/shared/worker/tests/browser/browser_worker-03.js
new file mode 100644
index 0000000000..185ba92d5e
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-03.js
@@ -0,0 +1,63 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the devtools/shared/worker can handle:
+// returned primitives (or promise or Error)
+//
+// And tests `workerify` by doing so.
+
+const { workerify } = require("resource://devtools/shared/worker/worker.js");
+function square(x) {
+  return x * x;
+}
+
+function squarePromise(x) {
+  return new Promise(resolve => resolve(x * x));
+}
+
+function squareError(x) {
+  return new Error("Nope");
+}
+
+function squarePromiseReject(x) {
+  return new Promise((_, reject) => reject("Nope"));
+}
+
+registerCleanupFunction(function () {
+  Services.prefs.clearUserPref("security.allow_parent_unrestricted_js_loads");
+});
+
+add_task(async function () {
+  // Needed for blob:null
+  Services.prefs.setBoolPref(
+    "security.allow_parent_unrestricted_js_loads",
+    true
+  );
+  let fn = workerify(square);
+  is(await fn(5), 25, "return primitives successful");
+  fn.destroy();
+
+  fn = workerify(squarePromise);
+  is(await fn(5), 25, "promise primitives successful");
+  fn.destroy();
+
+  fn = workerify(squareError);
+  try {
+    await fn(5);
+    ok(false, "return error should reject");
+  } catch (e) {
+    ok(true, "return error should reject");
+  }
+  fn.destroy();
+
+  fn = workerify(squarePromiseReject);
+  try {
+    await fn(5);
+    ok(false, "returned rejected promise rejects");
+  } catch (e) {
+    ok(true, "returned rejected promise rejects");
+  }
+  fn.destroy();
+});
diff --git a/devtools/shared/worker/worker.js b/devtools/shared/worker/worker.js
new file mode 100644
index 0000000000..4d753a928e
--- /dev/null
+++ b/devtools/shared/worker/worker.js
@@ -0,0 +1,198 @@
+/* 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/. */
+
+"use strict";
+
+/* global ChromeWorker */
+
+(function (factory) {
+  if (this.module && module.id.includes("worker")) {
+    // require
+    const dumpn = require("devtools/shared/DevToolsUtils").dumpn;
+    factory.call(
+      this,
+      require,
+      exports,
+      module,
+      { Cc, Ci, Cu },
+      ChromeWorker,
+      dumpn
+    );
+  } else {
+    // Cu.import
+    const { require } = ChromeUtils.importESModule(
+      "resource://devtools/shared/loader/Loader.sys.mjs"
+    );
+    this.isWorker = false;
+    this.console = console;
+    factory.call(
+      this,
+      require,
+      this,
+      { exports: this },
+      { Cc, Ci, Cu },
+      ChromeWorker,
+      null
+    );
+    this.EXPORTED_SYMBOLS = ["DevToolsWorker", "workerify"];
+  }
+}).call(
+  this,
+  function (require, exports, module, { Ci, Cc }, ChromeWorker, dumpn) {
+    let MESSAGE_COUNTER = 0;
+
+    /**
+     * 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
+     */
+    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);
+    }
+    exports.DevToolsWorker = DevToolsWorker;
+
+    /**
+     * 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}
+     */
+    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.
+      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;
+    }
+    exports.workerify = workerify;
+
+    /**
+     * 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()});`;
+    }
+  }
+);