Bug 898184 - Restore telemetry measurements that were removed when transitioning to the SessionWorker. r=ttaubert

browser/components/sessionstore/src/SessionWorker.js

@@ -21,8 +21,8 @@ let Decoder = new TextDecoder();
  * {fun:function_name, args:array_of_arguments_or_null, id: custom_id}
  *
  * Sends messages:
- * {ok: result, id: custom_id} / {fail: serialized_form_of_OS.File.Error,
- *                                id: custom_id}
+ * {ok: result, id: custom_id, telemetry: {}} /
+ * {fail: serialized_form_of_OS.File.Error, id: custom_id}
  */
 self.onmessage = function (msg) {
   let data = msg.data;
@@ -34,7 +34,7 @@ self.onmessage = function (msg) {
   let id = data.id;
 
   try {
-    result = Agent[data.fun].apply(Agent, data.args);
+    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
@@ -46,7 +46,11 @@ self.onmessage = function (msg) {
   // 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, id: id});
+  self.postMessage({
+    ok: result.result,
+    id: id,
+    telemetry: result.telemetry || {}
+  });
 };
 
 let Agent = {
@@ -100,24 +104,34 @@ let Agent = {
   read: function () {
     for (let path of [this.path, this.backupPath]) {
       try {
-        return this.initialState = Decoder.decode(File.read(path));
+        let durationMs = Date.now();
+        let bytes = File.read(path);
+        durationMs = Date.now() - durationMs;
+        this.initialState = Decoder.decode(bytes);
+
+        return {
+          result: this.initialState,
+          telemetry: {FX_SESSION_RESTORE_READ_FILE_MS: durationMs}
+        };
       } catch (ex if isNoSuchFileEx(ex)) {
         // Ignore exceptions about non-existent files.
       }
     }
-
     // No sessionstore data files found. Return an empty string.
-    return "";
+    return {result: ""};
   },
 
   /**
    * Write the session to disk.
    */
   write: function (stateString, options) {
+    let telemetry = {};
     if (!this.hasWrittenState) {
       if (options && options.backupOnFirstWrite) {
         try {
+          let startMs = Date.now();
           File.move(this.path, this.backupPath);
+          telemetry.FX_SESSION_RESTORE_BACKUP_FILE_MS = Date.now() - startMs;
         } catch (ex if isNoSuchFileEx(ex)) {
           // Ignore exceptions about non-existent files.
         }
@@ -126,8 +140,7 @@ let Agent = {
       this.hasWrittenState = true;
     }
 
-    let bytes = Encoder.encode(stateString);
-    return File.writeAtomic(this.path, bytes, {tmpPath: this.path + ".tmp"});
+    return this._write(stateString, telemetry);
   },
 
   /**
@@ -158,8 +171,18 @@ let Agent = {
 
     state.session = state.session || {};
     state.session.state = loadState;
-    let bytes = Encoder.encode(JSON.stringify(state));
-    return File.writeAtomic(this.path, bytes, {tmpPath: this.path + ".tmp"});
+    return this._write(JSON.stringify(state));
+  },
+
+  /**
+   * Write a stateString to disk
+   */
+  _write: function (stateString, telemetry = {}) {
+    let bytes = Encoder.encode(stateString);
+    let startMs = Date.now();
+    let result = File.writeAtomic(this.path, bytes, {tmpPath: this.path + ".tmp"});
+    telemetry.FX_SESSION_RESTORE_WRITE_FILE_MS = Date.now() - startMs;
+    return {result: result, telemetry: telemetry};
   },
 
   /**
@@ -167,10 +190,10 @@ let Agent = {
    */
   createBackupCopy: function (ext) {
     try {
-      return File.copy(this.path, this.backupPath + ext);
+      return {result: File.copy(this.path, this.backupPath + ext)};
     } catch (ex if isNoSuchFileEx(ex)) {
       // Ignore exceptions about non-existent files.
-      return true;
+      return {result: true};
     }
   },
 
@@ -179,10 +202,10 @@ let Agent = {
    */
   removeBackupCopy: function (ext) {
     try {
-      return File.remove(this.backupPath + ext);
+      return {result: File.remove(this.backupPath + ext)};
     } catch (ex if isNoSuchFileEx(ex)) {
       // Ignore exceptions about non-existent files.
-      return true;
+      return {result: true};
     }
   },
 
@@ -219,7 +242,7 @@ let Agent = {
       throw exn;
     }
 
-    return true;
+    return {result: true};
   }
 };
 

browser/components/sessionstore/src/_SessionFile.jsm

@@ -203,13 +203,15 @@ let SessionFileInternal = {
   },
 
   read: function () {
-    return SessionWorker.post("read").then(msg => msg.ok);
+    return SessionWorker.post("read").then(msg => {
+      this._recordTelemetry(msg.telemetry);
+      return msg.ok;
+    });
   },
 
   write: function (aData, aOptions) {
     let refObj = {};
     return TaskUtils.spawn(function task() {
-      TelemetryStopwatch.start("FX_SESSION_RESTORE_WRITE_FILE_MS", refObj);
       TelemetryStopwatch.start("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
 
       try {
@@ -217,12 +219,11 @@ let SessionFileInternal = {
         // At this point, we measure how long we stop the main thread
         TelemetryStopwatch.finish("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
 
-        // Now wait for the result and measure how long we had to wait for the result
-        yield promise;
-        TelemetryStopwatch.finish("FX_SESSION_RESTORE_WRITE_FILE_MS", refObj);
+        // Now wait for the result and record how long the write took
+        let msg = yield promise;
+        this._recordTelemetry(msg.telemetry);
       } catch (ex) {
         TelemetryStopwatch.cancel("FX_SESSION_RESTORE_WRITE_FILE_LONGEST_OP_MS", refObj);
-        TelemetryStopwatch.cancel("FX_SESSION_RESTORE_WRITE_FILE_MS", refObj);
         Cu.reportError("Could not write session state file " + this.path
                        + ": " + ex);
       }
@@ -230,7 +231,10 @@ let SessionFileInternal = {
   },
 
   writeLoadStateOnceAfterStartup: function (aLoadState) {
-    return SessionWorker.post("writeLoadStateOnceAfterStartup", [aLoadState]);
+    return SessionWorker.post("writeLoadStateOnceAfterStartup", [aLoadState]).then(msg => {
+      this._recordTelemetry(msg.telemetry);
+      return msg;
+    });
   },
 
   createBackupCopy: function (ext) {
@@ -243,6 +247,12 @@ let SessionFileInternal = {
 
   wipe: function () {
     return SessionWorker.post("wipe");
+  },
+
+  _recordTelemetry: function(telemetry) {
+    for (let histogramId in telemetry){
+      Telemetry.getHistogramById(histogramId).add(telemetry[histogramId]);
+    }
   }
 };