Add sync context dispatch restriction

ipc/ipc_sync_channel.h

 // Copyright (c) 2011 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.
 
 #ifndef IPC_IPC_SYNC_SENDER_H__
 #define IPC_IPC_SYNC_SENDER_H__
 #pragma once
 
 #include <string>
 #include <deque>
@@ skipping 33 matching lines @@
   virtual ~SyncChannel();
 
   virtual bool Send(Message* message);
   virtual bool SendWithTimeout(Message* message, int timeout_ms);
 
   // Whether we allow sending messages with no time-out.
   void set_sync_messages_with_no_timeout_allowed(bool value) {
     sync_messages_with_no_timeout_allowed_ = value;
   }
 
+  // Sets this channel to only dispatch its incoming unblocking messages when it
+  // is itself blocked on sending a sync message, not when other channels are.
+  //
+  // Normally, any unblocking message coming from any channel can be dispatched
+  // when any (possibly other) channel is blocked on sending a message. This is
+  // needed in some cases to unblock certain loops (e.g.
+  // renderer->browser->plugin->renderer), but may cause re-entrancy issues in
+  // some cases where loops are not possible (e.g. dispatching a ppapi message
+  // while the renderer is blocked on the gpu). This flags allows the tagging of
+  // some particular channels (e.g. ppapi) to not re-enter in such cases.

[jam, 2011/04/07 21:25:19]

nit: we've usually tried to stay away from talking about chrome specific
concepts in lower modules.  so can the comment be modified to not be specific to
renderer/ppapi etc?

+  void SetRestrictDispatchToSameChannel(bool value);
+
  protected:
   class ReceivedSyncMsgQueue;
   friend class ReceivedSyncMsgQueue;
 
   // SyncContext holds the per object data for SyncChannel, so that SyncChannel
   // can be deleted while it's being used in a different thread.  See
   // ChannelProxy::Context for more information.
   class SyncContext : public Context,
                       public base::WaitableEventWatcher::Delegate {
    public:
@@ skipping 27 matching lines @@
     // Called on the IPC thread when a sync send that runs a nested message loop
     // times out.
     void OnSendTimeout(int message_id);
 
     base::WaitableEvent* shutdown_event() { return shutdown_event_; }
 
     ReceivedSyncMsgQueue* received_sync_msgs() {
       return received_sync_msgs_;
     }
 
+    void set_restrict_dispatch(bool value) { restrict_dispatch_ = value; }
+    bool restrict_dispatch() const { return restrict_dispatch_; }
+
    private:
     ~SyncContext();
     // ChannelProxy methods that we override.
 
     // Called on the listener thread.
     virtual void Clear();
 
     // Called on the IPC thread.
     virtual bool OnMessageReceived(const Message& msg);
     virtual void OnChannelError();
     virtual void OnChannelOpened();
     virtual void OnChannelClosed();
 
     // Cancels all pending Send calls.
     void CancelPendingSends();
 
     // WaitableEventWatcher::Delegate implementation.
     virtual void OnWaitableEventSignaled(base::WaitableEvent* arg);
 
     typedef std::deque<PendingSyncMsg> PendingSyncMessageQueue;
     PendingSyncMessageQueue deserializers_;
     base::Lock deserializers_lock_;
 
     scoped_refptr<ReceivedSyncMsgQueue> received_sync_msgs_;
 
     base::WaitableEvent* shutdown_event_;
     base::WaitableEventWatcher shutdown_watcher_;
+    bool restrict_dispatch_;
   };
 
  private:
   // WaitableEventWatcher::Delegate implementation.
   virtual void OnWaitableEventSignaled(base::WaitableEvent* arg);
 
   SyncContext* sync_context() {
     return reinterpret_cast<SyncContext*>(context());
   }
 
@@ skipping 10 matching lines @@
 
   // Used to signal events between the IPC and listener threads.
   base::WaitableEventWatcher dispatch_watcher_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncChannel);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_SYNC_SENDER_H__