Introduce runtime.onSuspendCanceled() event.

chrome/browser/extensions/extension_process_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
@@ skipping 94 matching lines @@
 
 struct ExtensionProcessManager::BackgroundPageData {
   // The count of things keeping the lazy background page alive.
   int lazy_keepalive_count;
 
   // This is used with the ShouldUnload message, to ensure that the extension
   // remained idle between sending the message and receiving the ack.
   int close_sequence_id;
 
   // True if the page responded to the ShouldUnload message and is currently
-  // dispatching the unload event. We use this to ignore any activity
-  // generated during the unload event that would otherwise keep the
-  // extension alive.
+  // dispatching the unload event. During this time any events that arrive will
+  // cancel the unload process and an onSuspendCanceled event will be dispatched
+  // to the page.
   bool is_closing;

[benwells, 2012/07/19 04:01:21]

Can we change this name too? 

[koz (OOO until 15th September), 2012/07/19 06:52:11]

See previous comment.

 
   // Keeps track of when this page was last unloaded. Used for perf metrics.
   linked_ptr<PerfTimer> since_unloaded;
 
   BackgroundPageData()
       : lazy_keepalive_count(0), close_sequence_id(0), is_closing(false) {}
 };
 
 //
 // ExtensionProcessManager
@@ skipping 281 matching lines @@
     return 0;
 
   return background_page_data_[extension->id()].lazy_keepalive_count;
 }
 
 int ExtensionProcessManager::IncrementLazyKeepaliveCount(
      const Extension* extension) {
   if (!extension->has_lazy_background_page())
     return 0;
 
+  background_page_data_[extension->id()].is_closing = false;
   int& count = background_page_data_[extension->id()].lazy_keepalive_count;
   if (++count == 1)
     OnLazyBackgroundPageActive(extension->id());
 
   return count;
 }
 
 int ExtensionProcessManager::DecrementLazyKeepaliveCount(
      const Extension* extension) {
   if (!extension->has_lazy_background_page())
@@ skipping 55 matching lines @@
 void ExtensionProcessManager::OnShouldUnloadAck(
      const std::string& extension_id, int sequence_id) {
   ExtensionHost* host = GetBackgroundHostForExtension(extension_id);
   if (host &&
       sequence_id == background_page_data_[extension_id].close_sequence_id) {
     host->render_view_host()->Send(new ExtensionMsg_Unload(extension_id));
   }
 }
 
 void ExtensionProcessManager::OnUnloadAck(const std::string& extension_id) {
+  background_page_data_[extension_id].is_closing = true;
+  int sequence_id = background_page_data_[extension_id].close_sequence_id;
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&ExtensionProcessManager::CloseLazyBackgroundPageNow,
-                 weak_ptr_factory_.GetWeakPtr(), extension_id),
+                 weak_ptr_factory_.GetWeakPtr(), extension_id, sequence_id),
       event_page_unloading_time_);
 }
 
 void ExtensionProcessManager::CloseLazyBackgroundPageNow(
-    const std::string& extension_id) {
-  background_page_data_[extension_id].is_closing = true;
+    const std::string& extension_id, int sequence_id) {
   ExtensionHost* host = GetBackgroundHostForExtension(extension_id);
-  if (host)
-    CloseBackgroundHost(host);
+  if (host &&
+      sequence_id == background_page_data_[extension_id].close_sequence_id) {

[benwells, 2012/07/19 04:01:21]

Any change to sequence_id will cancel the unload. 

Is this the right set of events to cancel unload? I don't know what changes
sequence_id but it is probably more than an event being sent to the event page

A related question: can the unload be cancelled without the onSuspendCanceled
event being sent? It should not be possible.

[koz (OOO until 15th September), 2012/07/19 06:52:11]

Good point. I've changed it so that only dispatching an event can cause
onSuspendCancel().

+    ExtensionHost* host = GetBackgroundHostForExtension(extension_id);
+    if (host)
+      CloseBackgroundHost(host);
+  }
 }
 
 void ExtensionProcessManager::OnNetworkRequestStarted(
     RenderViewHost* render_view_host) {
   ExtensionHost* host = GetBackgroundHostForExtension(
       GetExtensionID(render_view_host));
   if (host && host->render_view_host() == render_view_host)
     IncrementLazyKeepaliveCount(host->extension());
 }
 
@@ skipping 261 matching lines @@
         if (service && service->is_ready())
           CreateBackgroundHostsForProfileStartup(this, service->extensions());
       }
       break;
     }
     default:
       ExtensionProcessManager::Observe(type, source, details);
       break;
   }
 }