Bug 1040761 - Re-add state info for experiments async shutdown blocker from bug 1012924. r=gfritzsche

browser/experiments/Experiments.jsm

@@ -351,11 +351,28 @@ AlreadyShutdownError.prototype.constructor = AlreadyShutdownError;
  */
 
 Experiments.Experiments = function (policy=new Experiments.Policy()) {
-  this._log = Log.repository.getLoggerWithMessagePrefix(
+  let log = Log.repository.getLoggerWithMessagePrefix(
       "Browser.Experiments.Experiments",
       "Experiments #" + gExperimentsCounter++ + "::");
+
+  // At the time of this writing, Experiments.jsm has severe
+  // crashes. For forensics purposes, keep the last few log
+  // messages in memory and upload them in case of crash.
+  this._forensicsLogs = [];
+  this._forensicsLogs.length = 3;
+  this._log = Object.create(log);
+  this._log.log = (level, string, params) => {
+    this._forensicsLogs.shift();
+    this._forensicsLogs.push(level + ": " + string);
+    log.log(level, string, params);
+  };
+
   this._log.trace("constructor");
 
+  // Capture the latest error, for forensics purposes.
+  this._latestError = null;
+
+
   this._policy = policy;
 
   // This is a Map of (string -> ExperimentEntry), keyed with the experiment id.
@@ -405,7 +422,10 @@ Experiments.Experiments.prototype = {
 
     gPrefsTelemetry.observe(PREF_TELEMETRY_ENABLED, this._telemetryStatusChanged, this);
 
-    AddonManager.shutdown.addBlocker("Experiments.jsm shutdown", this.uninit.bind(this));
+    AddonManager.shutdown.addBlocker("Experiments.jsm shutdown",
+      this.uninit.bind(this),
+      this._getState.bind(this)
+    );
 
     this._registerWithAddonManager();
 
@@ -419,6 +439,7 @@ Experiments.Experiments.prototype = {
       },
       (e) => {
         this._log.error("_loadFromCache caught error: " + e);
+        this._latestError = e;
         throw e;
       }
     );
@@ -462,12 +483,44 @@ Experiments.Experiments.prototype = {
         yield this._mainTask;
       } catch (e if e instanceof AlreadyShutdownError) {
         // We error out of tasks after shutdown via that exception.
+      } catch (e) {
+        this._latestError = e;
+        throw e;
       }
     }
 
     this._log.info("Completed uninitialization.");
   }),
 
+  // Return state information, for debugging purposes.
+  _getState: function() {
+    let state = {
+      isShutdown: this._shutdown,
+      isEnabled: gExperimentsEnabled,
+      isRefresh: this._refresh,
+      isDirty: this._dirty,
+      isFirstEvaluate: this._firstEvaluate,
+      hasLoadTask: !!this._loadTask,
+      hasMainTask: !!this._mainTask,
+      hasTimer: !!this._hasTimer,
+      hasAddonProvider: !!gAddonProvider,
+      latestLogs: this._forensicsLogs,
+      experiments: this._experiments.keys(),
+      terminateReason: this._terminateReason,
+    };
+    if (this._latestError) {
+      if (typeof this._latestError == "object") {
+        state.latestError = {
+          message: this._latestError.message,
+          stack: this._latestError.stack
+        };
+      } else {
+        state.latestError = "" + this._latestError;
+      }
+    }
+    return state;
+  },
+
   _registerWithAddonManager: function (previousExperimentsProvider) {
     this._log.trace("Registering instance with Addon Manager.");
 
@@ -493,9 +546,15 @@ Experiments.Experiments.prototype = {
 
   _unregisterWithAddonManager: function () {
     this._log.trace("Unregistering instance with Addon Manager.");
+
+    this._log.trace("Removing install listener from add-on manager.");
     AddonManager.removeInstallListener(this);
+    this._log.trace("Removing addon listener from add-on manager.");
     AddonManager.removeAddonListener(this);
+    this._log.trace("Finished unregistering with addon manager.");
+
     if (gAddonProvider) {
+      this._log.trace("Unregistering previous experiment add-on provider.");
       AddonManagerPrivate.unregisterProvider(gAddonProvider);
       gAddonProvider = null;
     }