michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0:  * You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: this.EXPORTED_SYMBOLS = ["SessionFile"];
michael@0: 
michael@0: /**
michael@0:  * Implementation of all the disk I/O required by the session store.
michael@0:  * This is a private API, meant to be used only by the session store.
michael@0:  * It will change. Do not use it for any other purpose.
michael@0:  *
michael@0:  * Note that this module implicitly depends on one of two things:
michael@0:  * 1. either the asynchronous file I/O system enqueues its requests
michael@0:  *   and never attempts to simultaneously execute two I/O requests on
michael@0:  *   the files used by this module from two distinct threads; or
michael@0:  * 2. the clients of this API are well-behaved and do not place
michael@0:  *   concurrent requests to the files used by this module.
michael@0:  *
michael@0:  * Otherwise, we could encounter bugs, especially under Windows,
michael@0:  *   e.g. if a request attempts to write sessionstore.js while
michael@0:  *   another attempts to copy that file.
michael@0:  *
michael@0:  * This implementation uses OS.File, which guarantees property 1.
michael@0:  */
michael@0: 
michael@0: const Cu = Components.utils;
michael@0: const Cc = Components.classes;
michael@0: const Ci = Components.interfaces;
michael@0: const Cr = Components.results;
michael@0: 
michael@0: Cu.import("resource://gre/modules/Services.jsm");
michael@0: Cu.import("resource://gre/modules/XPCOMUtils.jsm");
michael@0: Cu.import("resource://gre/modules/osfile.jsm");
michael@0: Cu.import("resource://gre/modules/osfile/_PromiseWorker.jsm", this);
michael@0: Cu.import("resource://gre/modules/Promise.jsm");
michael@0: Cu.import("resource://gre/modules/AsyncShutdown.jsm");
michael@0: 
michael@0: XPCOMUtils.defineLazyModuleGetter(this, "console",
michael@0:   "resource://gre/modules/devtools/Console.jsm");
michael@0: XPCOMUtils.defineLazyModuleGetter(this, "TelemetryStopwatch",
michael@0:   "resource://gre/modules/TelemetryStopwatch.jsm");
michael@0: XPCOMUtils.defineLazyModuleGetter(this, "Task",
michael@0:   "resource://gre/modules/Task.jsm");
michael@0: XPCOMUtils.defineLazyServiceGetter(this, "Telemetry",
michael@0:   "@mozilla.org/base/telemetry;1", "nsITelemetry");
michael@0: 
michael@0: this.SessionFile = {
michael@0:   /**
michael@0:    * Read the contents of the session file, asynchronously.
michael@0:    */
michael@0:   read: function () {
michael@0:     return SessionFileInternal.read();
michael@0:   },
michael@0:   /**
michael@0:    * Write the contents of the session file, asynchronously.
michael@0:    */
michael@0:   write: function (aData) {
michael@0:     return SessionFileInternal.write(aData);
michael@0:   },
michael@0:   /**
michael@0:    * Gather telemetry statistics.
michael@0:    *
michael@0:    *
michael@0:    * Most of the work is done off the main thread but there is a main
michael@0:    * thread cost involved to send data to the worker thread. This method
michael@0:    * should therefore be called only when we know that it will not disrupt
michael@0:    * the user's experience, e.g. on idle-daily.
michael@0:    *
michael@0:    * @return {Promise}
michael@0:    * @promise {object} An object holding all the information to be submitted
michael@0:    * to Telemetry.
michael@0:    */
michael@0:   gatherTelemetry: function(aData) {
michael@0:     return SessionFileInternal.gatherTelemetry(aData);
michael@0:   },
michael@0:   /**
michael@0:    * Create a backup copy, asynchronously.
michael@0:    * This is designed to perform backup on upgrade.
michael@0:    */
michael@0:   createBackupCopy: function (ext) {
michael@0:     return SessionFileInternal.createBackupCopy(ext);
michael@0:   },
michael@0:   /**
michael@0:    * Remove a backup copy, asynchronously.
michael@0:    * This is designed to clean up a backup on upgrade.
michael@0:    */
michael@0:   removeBackupCopy: function (ext) {
michael@0:     return SessionFileInternal.removeBackupCopy(ext);
michael@0:   },
michael@0:   /**
michael@0:    * Wipe the contents of the session file, asynchronously.
michael@0:    */
michael@0:   wipe: function () {
michael@0:     SessionFileInternal.wipe();
michael@0:   }
michael@0: };
michael@0: 
michael@0: Object.freeze(SessionFile);
michael@0: 
michael@0: /**
michael@0:  * Utilities for dealing with promises and Task.jsm
michael@0:  */
michael@0: let SessionFileInternal = {
michael@0:   /**
michael@0:    * The path to sessionstore.js
michael@0:    */
michael@0:   path: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.js"),
michael@0: 
michael@0:   /**
michael@0:    * The path to sessionstore.bak
michael@0:    */
michael@0:   backupPath: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.bak"),
michael@0: 
michael@0:   /**
michael@0:    * The promise returned by the latest call to |write|.
michael@0:    * We use it to ensure that AsyncShutdown.profileBeforeChange cannot
michael@0:    * interrupt a call to |write|.
michael@0:    */
michael@0:   _latestWrite: null,
michael@0: 
michael@0:   /**
michael@0:    * |true| once we have decided to stop receiving write instructiosn
michael@0:    */
michael@0:   _isClosed: false,
michael@0: 
michael@0:   read: function () {
michael@0:     // We must initialize the worker during startup so it will be ready to
michael@0:     // perform the final write. If shutdown happens soon after startup and
michael@0:     // the worker has not started yet we may not write.
michael@0:     // See Bug 964531.
michael@0:     SessionWorker.post("init");
michael@0: 
michael@0:     return Task.spawn(function*() {
michael@0:       for (let filename of [this.path, this.backupPath]) {
michael@0:         try {
michael@0:           let startMs = Date.now();
michael@0: 
michael@0:           let data = yield OS.File.read(filename, { encoding: "utf-8" });
michael@0: 
michael@0:           Telemetry.getHistogramById("FX_SESSION_RESTORE_READ_FILE_MS")
michael@0:                    .add(Date.now() - startMs);
michael@0: 
michael@0:           return data;
michael@0:         } catch (ex if ex instanceof OS.File.Error && ex.becauseNoSuchFile) {
michael@0:           // Ignore exceptions about non-existent files.
michael@0:         }
michael@0:       }
michael@0: 
michael@0:       return "";
michael@0:     }.bind(this));
michael@0:   },
michael@0: 
michael@0:   gatherTelemetry: function(aStateString) {
michael@0:     return Task.spawn(function() {
michael@0:       let msg = yield SessionWorker.post("gatherTelemetry", [aStateString]);
michael@0:       this._recordTelemetry(msg.telemetry);
michael@0:       throw new Task.Result(msg.telemetry);
michael@0:     }.bind(this));
michael@0:   },
michael@0: 
michael@0:   write: function (aData) {
michael@0:     if (this._isClosed) {
michael@0:       return Promise.reject(new Error("SessionFile is closed"));
michael@0:     }
michael@0:     let refObj = {};
michael@0: 
michael@0:     let isFinalWrite = false;
michael@0:     if (Services.startup.shuttingDown) {
michael@0:       // If shutdown has started, we will want to stop receiving
michael@0:       // write instructions.
michael@0:       isFinalWrite = this._isClosed = true;
michael@0:     }
michael@0: 
michael@0:     return this._latestWrite = Task.spawn(function task() {
michael@0:       TelemetryStopwatch.start("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
michael@0: 
michael@0:       try {
michael@0:         let promise = SessionWorker.post("write", [aData]);
michael@0:         // At this point, we measure how long we stop the main thread
michael@0:         TelemetryStopwatch.finish("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
michael@0: 
michael@0:         // Now wait for the result and record how long the write took
michael@0:         let msg = yield promise;
michael@0:         this._recordTelemetry(msg.telemetry);
michael@0:       } catch (ex) {
michael@0:         TelemetryStopwatch.cancel("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
michael@0:         console.error("Could not write session state file ", this.path, ex);
michael@0:       }
michael@0: 
michael@0:       if (isFinalWrite) {
michael@0:         Services.obs.notifyObservers(null, "sessionstore-final-state-write-complete", "");
michael@0:       }
michael@0:     }.bind(this));
michael@0:   },
michael@0: 
michael@0:   createBackupCopy: function (ext) {
michael@0:     return SessionWorker.post("createBackupCopy", [ext]);
michael@0:   },
michael@0: 
michael@0:   removeBackupCopy: function (ext) {
michael@0:     return SessionWorker.post("removeBackupCopy", [ext]);
michael@0:   },
michael@0: 
michael@0:   wipe: function () {
michael@0:     SessionWorker.post("wipe");
michael@0:   },
michael@0: 
michael@0:   _recordTelemetry: function(telemetry) {
michael@0:     for (let id of Object.keys(telemetry)){
michael@0:       let value = telemetry[id];
michael@0:       let samples = [];
michael@0:       if (Array.isArray(value)) {
michael@0:         samples.push(...value);
michael@0:       } else {
michael@0:         samples.push(value);
michael@0:       }
michael@0:       let histogram = Telemetry.getHistogramById(id);
michael@0:       for (let sample of samples) {
michael@0:         histogram.add(sample);
michael@0:       }
michael@0:     }
michael@0:   }
michael@0: };
michael@0: 
michael@0: // Interface to a dedicated thread handling I/O
michael@0: let SessionWorker = (function () {
michael@0:   let worker = new PromiseWorker("resource:///modules/sessionstore/SessionWorker.js",
michael@0:     OS.Shared.LOG.bind("SessionWorker"));
michael@0:   return {
michael@0:     post: function post(...args) {
michael@0:       let promise = worker.post.apply(worker, args);
michael@0:       return promise.then(
michael@0:         null,
michael@0:         function onError(error) {
michael@0:           // Decode any serialized error
michael@0:           if (error instanceof PromiseWorker.WorkerError) {
michael@0:             throw OS.File.Error.fromMsg(error.data);
michael@0:           }
michael@0:           // Extract something meaningful from ErrorEvent
michael@0:           if (error instanceof ErrorEvent) {
michael@0:             throw new Error(error.message, error.filename, error.lineno);
michael@0:           }
michael@0:           throw error;
michael@0:         }
michael@0:       );
michael@0:     }
michael@0:   };
michael@0: })();
michael@0: 
michael@0: // Ensure that we can write sessionstore.js cleanly before the profile
michael@0: // becomes unaccessible.
michael@0: AsyncShutdown.profileBeforeChange.addBlocker(
michael@0:   "SessionFile: Finish writing the latest sessionstore.js",
michael@0:   function() {
michael@0:     return SessionFileInternal._latestWrite;
michael@0:   });