Bug 1352157 - Avoid listTabs for global actors. r=ochameau

Adds a new `getRoot` request to the root actor which lists the global actors
only (leaving out the tabs).  This is a much better fit for callers who want to
access some global actor only, since it avoids visiting every tab, which could
be a very expensive operation.

MozReview-Commit-ID: 1lIAuaV7zoF

--HG--
extra : rebase_source : bf64ee1298591f26ffa4c6a660cca52145084b66

devtools/client/framework/target.js

@@ -277,7 +277,7 @@ TabTarget.prototype = {
     return this._form;
   },
 
-  // Get a promise of the root form returned by a listTabs request. This promise
+  // Get a promise of the root form returned by a getRoot request. This promise
   // is cached.
   get root() {
     if (!this._root) {
@@ -288,7 +288,7 @@ TabTarget.prototype = {
 
   _getRoot: function () {
     return new Promise((resolve, reject) => {
-      this.client.listTabs(response => {
+      this.client.mainRoot.getRoot(response => {
         if (response.error) {
           reject(new Error(response.error + ": " + response.message));
           return;

devtools/server/actors/root.js

@@ -244,11 +244,40 @@ RootActor.prototype = {
     this._processActors.clear();
   },
 
+  /**
+   * Gets the "root" form, which lists all the global actors that affect the entire
+   * browser.  This can replace usages of `listTabs` that only wanted the global actors
+   * and didn't actually care about tabs.
+   */
+  onGetRoot: function () {
+    let reply = {
+      from: this.actorID,
+    };
+
+    // Create global actors
+    if (!this._globalActorPool) {
+      this._globalActorPool = new ActorPool(this.conn);
+      this.conn.addActorPool(this._globalActorPool);
+    }
+    this._createExtraActors(this._parameters.globalActorFactories, this._globalActorPool);
+
+    // List the global actors
+    this._appendExtraActors(reply);
+
+    return reply;
+  },
+
   /* The 'listTabs' request and the 'tabListChanged' notification. */
 
   /**
    * Handles the listTabs request. The actors will survive until at least
    * the next listTabs request.
+   *
+   * ⚠ WARNING ⚠ This can be a very expensive operation, especially if there are many
+   * open tabs.  It will cause us to visit every tab, load a frame script, start a
+   * debugger server, and read some data.  With lazy tab support (bug 906076), this
+   * would trigger any lazy tabs to be loaded, greatly increasing resource usage.  Avoid
+   * this method whenever possible.
    */
   onListTabs: async function () {
     let tabList = this._parameters.tabList;
@@ -257,19 +286,14 @@ RootActor.prototype = {
                message: "This root actor has no browser tabs." };
     }
 
-    /*
-     * Now that a client has requested the list of tabs, we reattach the onListChanged
-     * listener in order to be notified if the list of tabs changes again in the future.
-     */
+    // Now that a client has requested the list of tabs, we reattach the onListChanged
+    // listener in order to be notified if the list of tabs changes again in the future.
     tabList.onListChanged = this._onTabListChanged;
 
-    /*
-     * Walk the tab list, accumulating the array of tab actors for the
-     * reply, and moving all the actors to a new ActorPool. We'll
-     * replace the old tab actor pool with the one we build here, thus
-     * retiring any actors that didn't get listed again, and preparing any
-     * new actors to receive packets.
-     */
+    // Walk the tab list, accumulating the array of tab actors for the reply, and moving
+    // all the actors to a new ActorPool. We'll replace the old tab actor pool with the
+    // one we build here, thus retiring any actors that didn't get listed again, and
+    // preparing any new actors to receive packets.
     let newActorPool = new ActorPool(this.conn);
     let tabActorList = [];
     let selected;
@@ -287,36 +311,23 @@ RootActor.prototype = {
       newActorPool.addActor(tabActor);
       tabActorList.push(tabActor);
     }
-    /* DebuggerServer.addGlobalActor support: create actors. */
-    if (!this._globalActorPool) {
-      this._globalActorPool = new ActorPool(this.conn);
-      this.conn.addActorPool(this._globalActorPool);
-    }
-    this._createExtraActors(this._parameters.globalActorFactories,
-      this._globalActorPool);
-    /*
-      * Drop the old actorID -> actor map. Actors that still mattered were
-      * added to the new map; others will go away.
-      */
+
+    // Start with the root reply, which includes the global actors for the whole browser.
+    let reply = this.onGetRoot();
+
+    // Drop the old actorID -> actor map. Actors that still mattered were added to the
+    // new map; others will go away.
     if (this._tabActorPool) {
       this.conn.removeActorPool(this._tabActorPool);
     }
     this._tabActorPool = newActorPool;
     this.conn.addActorPool(this._tabActorPool);
 
-    let reply = {
-      "from": this.actorID,
-      "selected": selected || 0,
-      "tabs": tabActorList.map(actor => actor.form())
-    };
-
-    /* If a root window is accessible, include its URL. */
-    if (this.url) {
-      reply.url = this.url;
-    }
-
-    /* DebuggerServer.addGlobalActor support: name actors in 'listTabs' reply. */
-    this._appendExtraActors(reply);
+    // We'll extend the reply here to also mention all the tabs.
+    Object.assign(reply, {
+      selected: selected || 0,
+      tabs: tabActorList.map(actor => actor.form()),
+    });
 
     return reply;
   },
@@ -586,16 +597,17 @@ RootActor.prototype = {
 };
 
 RootActor.prototype.requestTypes = {
-  "listTabs": RootActor.prototype.onListTabs,
-  "getTab": RootActor.prototype.onGetTab,
-  "getWindow": RootActor.prototype.onGetWindow,
-  "listAddons": RootActor.prototype.onListAddons,
-  "listWorkers": RootActor.prototype.onListWorkers,
-  "listServiceWorkerRegistrations": RootActor.prototype.onListServiceWorkerRegistrations,
-  "listProcesses": RootActor.prototype.onListProcesses,
-  "getProcess": RootActor.prototype.onGetProcess,
-  "echo": RootActor.prototype.onEcho,
-  "protocolDescription": RootActor.prototype.onProtocolDescription
+  getRoot: RootActor.prototype.onGetRoot,
+  listTabs: RootActor.prototype.onListTabs,
+  getTab: RootActor.prototype.onGetTab,
+  getWindow: RootActor.prototype.onGetWindow,
+  listAddons: RootActor.prototype.onListAddons,
+  listWorkers: RootActor.prototype.onListWorkers,
+  listServiceWorkerRegistrations: RootActor.prototype.onListServiceWorkerRegistrations,
+  listProcesses: RootActor.prototype.onListProcesses,
+  getProcess: RootActor.prototype.onGetProcess,
+  echo: RootActor.prototype.onEcho,
+  protocolDescription: RootActor.prototype.onProtocolDescription
 };
 
 exports.RootActor = RootActor;

devtools/shared/client/main.js

@@ -1652,6 +1652,13 @@ RootClient.prototype = {
   constructor: RootClient,
 
   /**
+   * Gets the "root" form, which lists all the global actors that affect the entire
+   * browser.  This can replace usages of `listTabs` that only wanted the global actors
+   * and didn't actually care about tabs.
+   */
+  getRoot: DebuggerClient.requester({ type: "getRoot" }),
+
+   /**
    * List the open tabs.
    *
    * @param function onResponse