Bug 845842 - Use promises that resolve on later ticks; r=rnewman

This is meant as a temporary workaround until a built-in promise library
offers similar functionality.

services/common/utils.js

@@ -6,6 +6,7 @@ const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
 
 this.EXPORTED_SYMBOLS = ["CommonUtils"];
 
+Cu.import("resource://gre/modules/commonjs/sdk/core/promise.js");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/osfile.jsm")
@@ -108,6 +109,19 @@ this.CommonUtils = {
     Services.tm.currentThread.dispatch(callback, Ci.nsIThread.DISPATCH_NORMAL);
   },
 
+  /**
+   * Return a promise resolving on some later tick.
+   *
+   * This a wrapper around Promise.resolve() that prevents stack
+   * accumulation and prevents callers from accidentally relying on
+   * same-tick promise resolution.
+   */
+  laterTickResolvingPromise: function (value, prototype) {
+    let deferred = Promise.defer(prototype);
+    this.nextTick(deferred.resolve.bind(deferred, value));
+    return deferred.promise;
+  },
+
   /**
    * Spin the event loop and return once the next tick is executed.
    *

services/healthreport/healthreporter.jsm

@@ -396,7 +396,7 @@ AbstractHealthReporter.prototype = Object.freeze({
     }
 
     if (this._initialized) {
-      return Promise.resolve(this);
+      return CommonUtils.laterTickResolvingPromise(this);
     }
 
     return this._initializedDeferred.promise;
@@ -793,7 +793,7 @@ AbstractHealthReporter.prototype = Object.freeze({
         let decoder = new TextDecoder();
         let json = JSON.parse(decoder.decode(buffer));
 
-        return Promise.resolve(json);
+        return CommonUtils.laterTickResolvingPromise(json);
       },
       function onError(error) {
         return Promise.reject(error);
@@ -1104,7 +1104,7 @@ HealthReporter.prototype = Object.freeze({
   _onBagheeraResult: function (request, isDelete, result) {
     this._log.debug("Received Bagheera result.");
 
-    let promise = Promise.resolve(null);
+    let promise = CommonUtils.laterTickResolvingPromise(null);
 
     if (!result.transportSuccess) {
       request.onSubmissionFailureSoft("Network transport error.");

services/healthreport/providers.jsm

@@ -391,7 +391,7 @@ CurrentSessionMeasurement.prototype = Object.freeze({
     fields.set("firstPaint", [now, sessions.firstPaint]);
     fields.set("sessionRestored", [now, sessions.sessionRestored]);
 
-    return Promise.resolve({
+    return CommonUtils.laterTickResolvingPromise({
       days: new Metrics.DailyValues(),
       singular: fields,
     });
@@ -626,14 +626,14 @@ AddonsProvider.prototype = Object.freeze({
     this._listener = listener;
     AddonManager.addAddonListener(this._listener);
 
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   onShutdown: function () {
     AddonManager.removeAddonListener(this._listener);
     this._listener = null;
 
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   collectConstantData: function () {

services/metrics/dataprovider.jsm

@@ -586,7 +586,7 @@ Provider.prototype = Object.freeze({
    * initialization activities have completed.
    */
   onInit: function () {
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   /**
@@ -599,7 +599,7 @@ Provider.prototype = Object.freeze({
    * shutdown activities have completed.
    */
   onShutdown: function () {
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   /**
@@ -611,7 +611,7 @@ Provider.prototype = Object.freeze({
    * @return Promise<>
    */
   collectConstantData: function () {
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   /**
@@ -627,7 +627,7 @@ Provider.prototype = Object.freeze({
    * @return Promise<>
    */
   collectDailyData: function () {
-    return Promise.resolve();
+    return CommonUtils.laterTickResolvingPromise();
   },
 
   /**

services/metrics/providermanager.jsm

@@ -153,7 +153,7 @@ this.ProviderManager.prototype = Object.freeze({
     }
 
     if (this._providers.has(provider.name)) {
-      return Promise.resolve();
+      return CommonUtils.laterTickResolvingPromise();
     }
 
     let deferred = Promise.defer();
@@ -222,13 +222,13 @@ this.ProviderManager.prototype = Object.freeze({
    */
   ensurePullOnlyProvidersRegistered: function () {
     if (this._pullOnlyProvidersRegistered) {
-      return Promise.resolve();
+      return CommonUtils.laterTickResolvingPromise();
     }
 
     let onFinished = function () {
       this._pullOnlyProvidersRegistered = true;
 
-      return Promise.resolve();
+      return CommonUtils.laterTickResolvingPromise();
     }.bind(this);
 
     return Task.spawn(function registerPullProviders() {
@@ -245,13 +245,13 @@ this.ProviderManager.prototype = Object.freeze({
 
   ensurePullOnlyProvidersUnregistered: function () {
     if (!this._pullOnlyProvidersRegistered) {
-      return Promise.resolve();
+      return CommonUtils.laterTickResolvingPromise();
     }
 
     let onFinished = function () {
       this._pullOnlyProvidersRegistered = false;
 
-      return Promise.resolve();
+      return CommonUtils.laterTickResolvingPromise();
     }.bind(this);
 
     return Task.spawn(function unregisterPullProviders() {
@@ -373,7 +373,7 @@ this.ProviderManager.prototype = Object.freeze({
           }
         }
 
-        return Promise.resolve(result);
+        return CommonUtils.laterTickResolvingPromise(result);
       });
 
       promises.push([provider.name, promise]);

services/metrics/storage.jsm

@@ -980,7 +980,8 @@ MetricsStorageSqliteBackend.prototype = Object.freeze({
    */
   registerMeasurement: function (provider, name, version) {
     if (this.hasMeasurement(provider, name, version)) {
-      return Promise.resolve(this.measurementID(provider, name, version));
+      return CommonUtils.laterTickResolvingPromise(
+        this.measurementID(provider, name, version));
     }
 
     // Registrations might not be safe to perform in parallel with provider
@@ -1067,7 +1068,8 @@ MetricsStorageSqliteBackend.prototype = Object.freeze({
         throw new Error("Field already defined with different type: " + existingType);
       }
 
-      return Promise.resolve(this.fieldIDFromMeasurement(measurementID, field));
+      return CommonUtils.laterTickResolvingPromise(
+        this.fieldIDFromMeasurement(measurementID, field));
     }
 
     let self = this;