[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/public/cpp/bindings/binding.h

 // Copyright 2014 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 MOJO_PUBLIC_CPP_BINDINGS_BINDING_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_BINDING_H_
 
 #include <utility>
 
 #include "base/macros.h"
@@ skipping 190 matching lines @@
   MessagePipeHandle handle() const { return internal_state_.handle(); }
 
   // Returns the associated group that this object belongs to. Returns null if:
   //   - this object is not bound; or
   //   - the interface doesn't have methods to pass associated interface
   //     pointers or requests.
   AssociatedGroup* associated_group() {
     return internal_state_.associated_group();
   }
 
+  // Allows synchronous dispatch for this Binding. When sync dispatch is

[yzshen1, 2016/03/16 15:38:18]

This comment also needs to mention bindings living on the IO thread and the
client is out of process. And likely that is the only case that we would like to
use this feature. Is that correct?

I feel that this is something related to our implementation details and hard to
explain clearly as a public API. I wonder whether we can have a flag passed into
the watcher API's callback, indicating whether the signal state change is
directly resulted from a Mojo system API call (as opposed to receiving a message
from another process). If it is not, then we should be safe to do sync
dispatching, right?

If the approach above is not possible, maybe we should consider a different
method name. The current name sounds to me that it is related to sync method
call.

WDYT? I am happy to chat about this in person if that is more convenient.

+  // allowed, a client on the same thread as this Binding will synchronously
+  // enter the bound implementation when writing messages to its pipe.
+  //
+  // Note that this also allows synchronous dispatch for any endpoints
+  // which are associated with this one and which live on the same thread.
+  void SetAllowSyncDispatch(bool allowed) {
+    internal_state_.SetAllowSyncDispatch(allowed);
+  }
+
   // Exposed for testing, should not generally be used.
   void EnableTestingMode() { internal_state_.EnableTestingMode(); }
 
  private:
   internal::BindingState<Interface, Interface::PassesAssociatedKinds_>
       internal_state_;
 
   DISALLOW_COPY_AND_ASSIGN(Binding);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_BINDING_H_