Make ChannelMojo Send thread-safe

Changes ChannelMojo to write outgoing Receive requests
directly to the pipe rather than using its
AssociatedInterfacePtr. The associated interface ID is
still included in each outgoing message.

This lets us mark ChannelMojo::Send as thread-safe, avoiding
a thread-hop when sending IPCs through IPC::ChannelProxy.

BUG=595082

Review URL: https://codereview.chromium.org/1825543002

Cr-Commit-Position: refs/heads/master@{#382762}

1 files changed, 21 insertions, 7 deletions

diff --git a/ipc/mojo/ipc_message_pipe_reader.h b/ipc/mojo/ipc_message_pipe_reader.h
index 3989c25..d2ba9de 100644
--- a/ipc/mojo/ipc_message_pipe_reader.h
+++ b/ipc/mojo/ipc_message_pipe_reader.h
@@ -19,6 +19,7 @@
 #include "ipc/mojo/ipc.mojom.h"
 #include "mojo/public/cpp/bindings/associated_binding.h"
 #include "mojo/public/cpp/system/core.h"
+#include "mojo/public/cpp/system/message_pipe.h"
 
 namespace IPC {
 namespace internal {
@@ -46,8 +47,7 @@ class MessagePipeReader : public mojom::Channel {
   class Delegate {
    public:
     virtual void OnMessageReceived(const Message& message) = 0;
-    virtual void OnPipeClosed(MessagePipeReader* reader) = 0;
-    virtual void OnPipeError(MessagePipeReader* reader) = 0;
+    virtual void OnPipeError() = 0;
   };
 
   // Delay the object deletion using the current message loop.
@@ -65,11 +65,18 @@ class MessagePipeReader : public mojom::Channel {
     void operator()(MessagePipeReader* ptr) const;
   };
 
-  // Both parameters must be non-null.
-  // Build a reader that reads messages from |receive_handle| and lets
+  // Builds a reader that reads messages from |receive_handle| and lets
   // |delegate| know.
+  //
+  // |pipe| is the message pipe handle corresponding to the channel's master
+  // interface. This is the message pipe underlying both |sender| and
+  // |receiver|.
+  //
+  // Both |sender| and |receiver| must be non-null.
+  //
   // Note that MessagePipeReader doesn't delete |delegate|.
-  MessagePipeReader(mojom::ChannelAssociatedPtr sender,
+  MessagePipeReader(mojo::MessagePipeHandle pipe,
+                    mojom::ChannelAssociatedPtr sender,
                     mojo::AssociatedInterfaceRequest<mojom::Channel> receiver,
                     base::ProcessId peer_pid,
                     Delegate* delegate);
@@ -77,12 +84,12 @@ class MessagePipeReader : public mojom::Channel {
 
   // Close and destroy the MessagePipe.
   void Close();
-  // Close the mesage pipe with notifying the client with the error.
-  void CloseWithError(MojoResult error);
 
   // Return true if the MessagePipe is alive.
   bool IsValid() { return sender_; }
 
+  // Sends an IPC::Message to the other end of the pipe. Safe to call from any
+  // thread.
   bool Send(scoped_ptr<Message> message);
 
   base::ProcessId GetPeerPid() const { return peer_pid_; }
@@ -92,6 +99,7 @@ class MessagePipeReader : public mojom::Channel {
   void OnPipeError(MojoResult error);
 
  private:
+  // mojom::Channel:
   void Receive(mojo::Array<uint8_t> data,
                mojo::Array<mojom::SerializedHandlePtr> handles) override;
 
@@ -100,6 +108,12 @@ class MessagePipeReader : public mojom::Channel {
   base::ProcessId peer_pid_;
   mojom::ChannelAssociatedPtr sender_;
   mojo::AssociatedBinding<mojom::Channel> binding_;
+
+  // Raw message pipe handle and interface ID we use to send legacy IPC messages
+  // over the associated pipe.
+  const uint32_t sender_interface_id_;
+  const mojo::MessagePipeHandle sender_pipe_;
+
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(MessagePipeReader);