Fix bug where content scripts can get GC'd if they don't attach

chrome/renderer/extensions/event_bindings.cc

 // Copyright (c) 2009 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 "chrome/renderer/extensions/event_bindings.h"
 
 #include "base/basictypes.h"
 #include "base/singleton.h"
 #include "chrome/common/render_messages.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/renderer/extensions/bindings_utils.h"
 #include "chrome/renderer/extensions/event_bindings.h"
 #include "chrome/renderer/extensions/js_only_v8_extensions.h"
 #include "chrome/renderer/render_thread.h"
 #include "chrome/renderer/render_view.h"
 #include "grit/renderer_resources.h"
 #include "webkit/api/public/WebDataSource.h"
 #include "webkit/api/public/WebFrame.h"
 #include "webkit/api/public/WebURLRequest.h"
 
 using bindings_utils::CallFunctionInContext;
 using bindings_utils::ContextInfo;
 using bindings_utils::ContextList;
 using bindings_utils::GetContexts;
+using bindings_utils::GetInfoForCurrentContext;
 using bindings_utils::GetStringResource;
 using bindings_utils::ExtensionBase;
 using bindings_utils::GetPendingRequestMap;
 using bindings_utils::PendingRequestMap;
 using WebKit::WebFrame;
 
+static void ContextWeakReferenceCallback(v8::Persistent<v8::Value> context,
+                                         void*);
+
 namespace {
 
 // Keep a local cache of RenderThread so that we can mock it out for unit tests.
 static RenderThreadBase* render_thread = NULL;
 static bool in_unit_tests = false;
 
 // Set to true if these bindings are registered.  Will be false when extensions
 // are disabled.
 static bool bindings_registered = false;
 
@@ skipping 31 matching lines @@
   // Attach an event name to an object.
   static v8::Handle<v8::Value> AttachEvent(const v8::Arguments& args) {
     DCHECK(args.Length() == 1);
     // TODO(erikkay) should enforce that event name is a string in the bindings
     DCHECK(args[0]->IsString() || args[0]->IsUndefined());
 
     if (args[0]->IsString()) {
       std::string event_name(*v8::String::AsciiValue(args[0]));
       bool has_permission =
           ExtensionProcessBindings::CurrentContextHasPermission(event_name);
-#if EXTENSION_TIME_TO_BREAK_API
       bool allow_api = has_permission;

[Matt Perry, 2009/09/14 18:07:47]

may as well remove this and use has_permission directly

-#else
-      bool allow_api = true;
-#endif
 
       // Increment the count even if the caller doesn't have permission, so that
       // refcounts stay balanced.
       if (EventIncrementListenerCount(event_name) == 1 && allow_api) {
         EventBindings::GetRenderThread()->Send(
             new ViewHostMsg_ExtensionAddListener(event_name));
       }
 
+      ContextInfo* current_context_info = GetInfoForCurrentContext();
+      if (++current_context_info->num_connected_events == 1)
+        current_context_info->context.ClearWeak();
+
       if (!has_permission) {
         return ExtensionProcessBindings::ThrowPermissionDeniedException(
             event_name);
       }
     }
 
     return v8::Undefined();
   }
 
   static v8::Handle<v8::Value> DetachEvent(const v8::Arguments& args) {
     DCHECK(args.Length() == 1);
     // TODO(erikkay) should enforce that event name is a string in the bindings
     DCHECK(args[0]->IsString() || args[0]->IsUndefined());
 
     if (args[0]->IsString()) {
       std::string event_name(*v8::String::AsciiValue(args[0]));
       if (EventDecrementListenerCount(event_name) == 0) {
         EventBindings::GetRenderThread()->Send(
           new ViewHostMsg_ExtensionRemoveListener(event_name));
       }
+
+      ContextInfo* current_context_info = GetInfoForCurrentContext();
+      if (current_context_info &&

[Matt Perry, 2009/09/14 18:07:47]

why the NULL-check here but not in AttachEvent?

+          --current_context_info->num_connected_events == 0) {
+        current_context_info->context.MakeWeak(NULL,
+            &ContextWeakReferenceCallback);
+      }
     }
 
     return v8::Undefined();
   }
 };
 
 }  // namespace
 
 const char* EventBindings::kName = "chrome/EventBindings";
 
@@ skipping 169 matching lines @@
     // TODO(rafaelw): Consider only doing this check if function_name ==
     // "Event.dispatchJSON".
 #ifdef _DEBUG
     if (!retval.IsEmpty() && !retval->IsUndefined()) {
       std::string error = *v8::String::AsciiValue(retval);
       DCHECK(false) << error;
     }
 #endif
   }
 }