Bug 965137 - Synchronously write session on application-background. r=mfinkle

mobile/android/components/SessionStore.js

@@ -43,6 +43,7 @@ SessionStore.prototype = {
   _lastSaveTime: 0,
   _interval: 10000,
   _maxTabsUndo: 1,
+  _pendingWrite: 0,
 
   init: function ss_init() {
     // Get file references
@@ -77,6 +78,7 @@ SessionStore.prototype = {
         observerService.addObserver(this, "domwindowclosed", true);
         observerService.addObserver(this, "browser:purge-session-history", true);
         observerService.addObserver(this, "Session:Restore", true);
+        observerService.addObserver(this, "application-background", true);
         break;
       case "final-ui-startup":
         observerService.removeObserver(this, "final-ui-startup");
@@ -102,7 +104,7 @@ SessionStore.prototype = {
 
         if (this._loadState == STATE_RUNNING) {
           // Save the purged state immediately
-          this.saveStateNow();
+          this.saveState();
         }
 
         Services.obs.notifyObservers(null, "sessionstore-state-purge-complete", "");
@@ -110,7 +112,9 @@ SessionStore.prototype = {
       case "timer-callback":
         // Timer call back for delayed saving
         this._saveTimer = null;
-        this.saveState();
+        if (this._pendingWrite) {
+          this.saveState();
+        }
         break;
       case "Session:Restore": {
         if (aData) {
@@ -143,6 +147,13 @@ SessionStore.prototype = {
         }
         break;
       }
+      case "application-background":
+        // We receive this notification when Android's onPause callback is
+        // executed. After onPause, the application may be terminated at any
+        // point without notice; therefore, we must synchronously write out any
+        // pending save state to ensure that this data does not get lost.
+        this.flushPendingState();
+        break;
     }
   },
 
@@ -306,7 +317,7 @@ SessionStore.prototype = {
 
       delete aBrowser.__SS_data;
       this._collectTabData(aWindow, aBrowser, data);
-      this.saveStateNow();
+      this.saveState();
     }
 
     this._updateCrashReportURL(aWindow);
@@ -342,6 +353,7 @@ SessionStore.prototype = {
       // If we have to wait, set a timer, otherwise saveState directly
       let delay = Math.max(minimalDelay, 2000);
       if (delay > 0) {
+        this._pendingWrite++;
         this._saveTimer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
         this._saveTimer.init(this, delay, Ci.nsITimer.TYPE_ONE_SHOT);
       } else {
@@ -350,16 +362,25 @@ SessionStore.prototype = {
     }
   },
 
-  saveStateNow: function ss_saveStateNow() {
+  saveState: function ss_saveState() {
+    this._pendingWrite++;
+    this._saveState(true);
+  },
+
+  // Immediately and synchronously writes any pending state to disk.
+  flushPendingState: function ss_flushPendingState() {
+    if (this._pendingWrite) {
+      this._saveState(false);
+    }
+  },
+
+  _saveState: function ss_saveState(aAsync) {
     // Kill any queued timer and save immediately
     if (this._saveTimer) {
       this._saveTimer.cancel();
       this._saveTimer = null;
     }
-    this.saveState();
-  },
 
-  saveState: function ss_saveState() {
     let data = this._getCurrentState();
     let normalData = { windows: [] };
     let privateData = { windows: [] };
@@ -388,7 +409,7 @@ SessionStore.prototype = {
     }
 
     // Write only non-private data to disk
-    this._writeFile(this._sessionFile, JSON.stringify(normalData));
+    this._writeFile(this._sessionFile, JSON.stringify(normalData), aAsync);
 
     // If we have private data, send it to Java; otherwise, send null to
     // indicate that there is no private data
@@ -464,7 +485,7 @@ SessionStore.prototype = {
     }
   },
 
-  _writeFile: function ss_writeFile(aFile, aData) {
+  _writeFile: function ss_writeFile(aFile, aData, aAsync) {
     let stateString = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
     stateString.data = aData;
     Services.obs.notifyObservers(stateString, "sessionstore-state-write", "");
@@ -473,11 +494,28 @@ SessionStore.prototype = {
     if (!stateString.data)
       return;
 
-    // Asynchronously copy the data to the file.
-    let array = new TextEncoder().encode(aData);
-    OS.File.writeAtomic(aFile.path, array, { tmpPath: aFile.path + ".tmp" }).then(function onSuccess() {
-      Services.obs.notifyObservers(null, "sessionstore-state-write-complete", "");
-    });
+    if (aAsync) {
+      let array = new TextEncoder().encode(aData);
+      let pendingWrite = this._pendingWrite;
+      OS.File.writeAtomic(aFile.path, array, { tmpPath: aFile.path + ".tmp" }).then(function onSuccess() {
+        // Make sure this._pendingWrite is the same value it was before we
+        // fired off the async write. If the count is different, another write
+        // is pending, so we shouldn't reset this._pendingWrite yet.
+        if (pendingWrite === this._pendingWrite)
+          this._pendingWrite = 0;
+        Services.obs.notifyObservers(null, "sessionstore-state-write-complete", "");
+      }.bind(this));
+    } else {
+      this._pendingWrite = 0;
+      let foStream = Cc["@mozilla.org/network/file-output-stream;1"].
+                     createInstance(Ci.nsIFileOutputStream);
+      foStream.init(aFile, 0x02 | 0x08 | 0x20, 0666, 0);
+      let converter = Cc["@mozilla.org/intl/converter-output-stream;1"].
+                      createInstance(Ci.nsIConverterOutputStream);
+      converter.init(foStream, "UTF-8", 0, 0);
+      converter.writeString(aData);
+      converter.close();
+    }
   },
 
   _updateCrashReportURL: function ss_updateCrashReportURL(aWindow) {