Bug 801598 - Making SessionWorker use the now public PromiseWorker API. r=ttaubert

browser/components/sessionstore/src/SessionFile.jsm

@@ -33,7 +33,6 @@ const Cr = Components.results;
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/osfile.jsm");
-Cu.import("resource://gre/modules/osfile/_PromiseWorker.jsm", this);
 Cu.import("resource://gre/modules/Promise.jsm");
 Cu.import("resource://gre/modules/AsyncShutdown.jsm");
 
@@ -193,13 +192,6 @@ let SessionFileInternal = {
     }
   },
 
-  /**
-   * The promise returned by the latest call to |write|.
-   * We use it to ensure that AsyncShutdown.profileBeforeChange cannot
-   * interrupt a call to |write|.
-   */
-  _latestWrite: null,
-
   /**
    * |true| once we have decided to stop receiving write instructiosn
    */
@@ -278,9 +270,17 @@ let SessionFileInternal = {
       isFinalWrite = this._isClosed = true;
     }
 
-    return this._latestWrite = Task.spawn(function* task() {
+    let deferredWritten = Promise.defer();
+    return Task.spawn(function* task() {
       TelemetryStopwatch.start("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
 
+      // Ensure that we can write sessionstore.js cleanly before the profile
+      // becomes unaccessible.
+      AsyncShutdown.profileBeforeChange.addBlocker(
+        "SessionFile: Finish writing Session Restore data",
+        deferredWritten.promise
+      );
+
       try {
         let performShutdownCleanup = isFinalWrite &&
           !sessionStartup.isAutomaticRestoreEnabled();
@@ -296,14 +296,18 @@ let SessionFileInternal = {
         let msg = yield promise;
         this._recordTelemetry(msg.telemetry);
 
-        if (msg.ok && msg.ok.upgradeBackup) {
+        if (msg.result.upgradeBackup) {
           // We have just completed a backup-on-upgrade, store the information
           // in preferences.
           Services.prefs.setCharPref(PREF_UPGRADE_BACKUP, Services.appinfo.platformBuildID);
         }
+        deferredWritten.resolve();
       } catch (ex) {
         TelemetryStopwatch.cancel("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
         console.error("Could not write session state file ", ex, ex.stack);
+        deferredWritten.reject(ex);
+      } finally {
+        AsyncShutdown.profileBeforeChange.removeBlocker(deferredWritten.promise);
       }
 
       if (isFinalWrite) {
@@ -332,11 +336,3 @@ let SessionFileInternal = {
     }
   }
 };
-
-// Ensure that we can write sessionstore.js cleanly before the profile
-// becomes unaccessible.
-AsyncShutdown.profileBeforeChange.addBlocker(
-  "SessionFile: Finish writing the latest sessionstore.js",
-  function() {
-    return SessionFileInternal._latestWrite;
-  });

browser/components/sessionstore/src/SessionWorker.js

@@ -10,48 +10,24 @@
 
 importScripts("resource://gre/modules/osfile.jsm");
 
+let PromiseWorker = require("resource://gre/modules/workers/PromiseWorker.js");
+
 let File = OS.File;
 let Encoder = new TextEncoder();
 let Decoder = new TextDecoder();
 
-/**
- * Communications with the controller.
- *
- * Accepts messages:
- * {fun:function_name, args:array_of_arguments_or_null, id: custom_id}
- *
- * Sends messages:
- * {ok: result, id: custom_id, telemetry: {}} /
- * {fail: serialized_form_of_OS.File.Error, id: custom_id}
- */
-self.onmessage = function (msg) {
-  let data = msg.data;
-  if (!(data.fun in Agent)) {
-    throw new Error("Cannot find method " + data.fun);
-  }
-
-  let result;
-  let id = data.id;
-
-  try {
-    result = Agent[data.fun].apply(Agent, data.args) || {};
-  } catch (ex if ex instanceof OS.File.Error) {
-    // Instances of OS.File.Error know how to serialize themselves
-    // (deserialization ensures that we end up with OS-specific
-    // instances of |OS.File.Error|)
-    self.postMessage({fail: OS.File.Error.toMsg(ex), id: id});
-    return;
-  }
-
-  // Other exceptions do not, and should be propagated through DOM's
-  // built-in mechanism for uncaught errors, although this mechanism
-  // may lose interesting information.
-  self.postMessage({
-    ok: result.result,
-    id: id,
-    telemetry: result.telemetry || {}
-  });
+let worker = new PromiseWorker.AbstractWorker();
+worker.dispatch = function(method, args = []) {
+  return Agent[method](...args);
 };
+worker.postMessage = function(result, ...transfers) {
+  self.postMessage(result, ...transfers);
+};
+worker.close = function() {
+  self.close();
+};
+
+self.addEventListener("message", msg => worker.handleMessage(msg));
 
 // The various possible states
 

browser/components/sessionstore/src/SessionWorker.jsm

@@ -13,31 +13,13 @@ const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cr = Components.results;
 
-Cu.import("resource://gre/modules/osfile/_PromiseWorker.jsm", this);
+Cu.import("resource://gre/modules/PromiseWorker.jsm", this);
 Cu.import("resource://gre/modules/osfile.jsm", this);
 
 this.EXPORTED_SYMBOLS = ["SessionWorker"];
 
-this.SessionWorker = (function () {
-  let worker = new PromiseWorker("resource:///modules/sessionstore/SessionWorker.js",
-    OS.Shared.LOG.bind("SessionWorker"));
-  return {
-    post: function post(...args) {
-      let promise = worker.post.apply(worker, args);
-      return promise.then(
-        null,
-        function onError(error) {
-          // Decode any serialized error
-          if (error instanceof PromiseWorker.WorkerError) {
-            throw OS.File.Error.fromMsg(error.data);
-          }
-          // Extract something meaningful from ErrorEvent
-          if (error instanceof ErrorEvent) {
-            throw new Error(error.message, error.filename, error.lineno);
-          }
-          throw error;
-        }
-      );
-    }
-  };
-})();
+this.SessionWorker = new BasePromiseWorker("resource:///modules/sessionstore/SessionWorker.js");
+// As the Session Worker performs I/O, we can receive instances of
+// OS.File.Error, so we need to install a decoder.
+this.SessionWorker.ExceptionHandlers["OS.File.Error"] = OS.File.Error.fromMsg;
+