Bug 549888: Part 1: Let the channel listener decide how to mediate RPC races, defaulting to "child wins". r=bent

ipc/glue/RPCChannel.cpp

@@ -89,15 +89,13 @@ public:
 namespace mozilla {
 namespace ipc {
 
-RPCChannel::RPCChannel(RPCListener* aListener,
-                       RacyRPCPolicy aPolicy)
+RPCChannel::RPCChannel(RPCListener* aListener)
   : SyncChannel(aListener),
     mPending(),
     mStack(),
     mOutOfTurnReplies(),
     mDeferred(),
     mRemoteStackDepthGuess(0),
-    mRacePolicy(aPolicy),
     mBlockedOnParent(false),
     mCxxStackFrames(0)
 {
@@ -422,7 +420,8 @@ RPCChannel::Incall(const Message& call, size_t stackDepth)
         // the other side's in-call
         bool defer;
         const char* winner;
-        switch (mRacePolicy) {
+        switch (Listener()->MediateRPCRace(mChild ? call : mStack.top(),
+                                           mChild ? mStack.top() : call)) {
         case RRPChildWins:
             winner = "child";
             defer = mChild;
@@ -470,8 +469,7 @@ RPCChannel::DispatchIncall(const Message& call)
     Message* reply = nsnull;
 
     ++mRemoteStackDepthGuess;
-    Result rv =
-        static_cast<RPCListener*>(mListener)->OnCallReceived(call, reply);
+    Result rv = Listener()->OnCallReceived(call, reply);
     --mRemoteStackDepthGuess;
 
     if (!MaybeHandleError(rv, "RPCChannel")) {

ipc/glue/RPCChannel.h

@@ -55,6 +55,13 @@ class RPCChannel : public SyncChannel
     friend class CxxStackFrame;
 
 public:
+    // What happens if RPC calls race?
+    enum RacyRPCPolicy {
+        RRPError,
+        RRPChildWins,
+        RRPParentWins
+    };
+
     class /*NS_INTERFACE_CLASS*/ RPCListener :
         public SyncChannel::SyncListener
     {
@@ -78,17 +85,16 @@ public:
         virtual void OnExitedCxxStack()
         {
             NS_RUNTIMEABORT("default impl shouldn't be invoked");
-        }   
+        }
+
+        virtual RacyRPCPolicy MediateRPCRace(const Message& parent,
+                                             const Message& child)
+        {
+            return RRPChildWins;
+        }
     };
 
-    // What happens if RPC calls race?
-    enum RacyRPCPolicy {
-        RRPError,
-        RRPChildWins,
-        RRPParentWins
-    };
-
-    RPCChannel(RPCListener* aListener, RacyRPCPolicy aPolicy=RRPChildWins);
+    RPCChannel(RPCListener* aListener);
 
     virtual ~RPCChannel();
 
@@ -167,6 +173,10 @@ protected:
   private:
     // Called on worker thread only
 
+    RPCListener* Listener() const {
+        return static_cast<RPCListener*>(mListener);
+    }
+
     bool EventOccurred();
 
     void MaybeProcessDeferredIncall();
@@ -185,12 +195,12 @@ protected:
     // for when the depth goes from non-zero to zero;
     void EnteredCxxStack()
     {
-        static_cast<RPCListener*>(mListener)->OnEnteredCxxStack();
+        Listener()->OnEnteredCxxStack();
     }
 
     void ExitedCxxStack()
     {
-        static_cast<RPCListener*>(mListener)->OnExitedCxxStack();
+        Listener()->OnExitedCxxStack();
     }
 
     class NS_STACK_CLASS CxxStackFrame
@@ -327,7 +337,6 @@ protected:
     // detect the same race.
     //
     size_t mRemoteStackDepthGuess;
-    RacyRPCPolicy mRacePolicy;
 
     // True iff the parent has put us in a |BlockChild()| state.
     bool mBlockedOnParent;

ipc/ipdl/ipdl/lower.py

@@ -2662,7 +2662,7 @@ class _GenerateProtocolActorCode(ipdl.ast.Visitor):
                                 Whitespace.NL ])
 
         self.cls.addstmts((
-            [ Label.PRIVATE ]
+            [ Label.PUBLIC ]
             + self.standardTypedefs()
             + [ Whitespace.NL ]
         ))