From 3bd6fe6f31f6f7154f9d517e83a473afcab76b63 Mon Sep 17 00:00:00 2001
From: Ben Turner <bent.mozilla@gmail.com>
Date: Fri, 8 Aug 2014 18:19:33 -0700
Subject: [PATCH] Bug 1044322 - Reset the channel listener on the correct
 thread, r=bsmedberg.

---
 ipc/glue/MessageLink.cpp | 32 +++++++++++++++++++++-----------
 ipc/glue/MessageLink.h   |  8 ++++++++
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/ipc/glue/MessageLink.cpp b/ipc/glue/MessageLink.cpp
index 299902e131e1..868bde8021ca 100644
--- a/ipc/glue/MessageLink.cpp
+++ b/ipc/glue/MessageLink.cpp
@@ -15,6 +15,7 @@
 #include "mozilla/Preferences.h"
 #endif
 
+#include "mozilla/Assertions.h"
 #include "nsDebug.h"
 #include "nsISupportsImpl.h"
 #include "nsXULAppAPI.h"
@@ -58,25 +59,26 @@ MessageLink::MessageLink(MessageChannel *aChan)
 
 MessageLink::~MessageLink()
 {
+#ifdef DEBUG
     mChan = nullptr;
+#endif
 }
 
 ProcessLink::ProcessLink(MessageChannel *aChan)
-  : MessageLink(aChan),
-    mExistingListener(nullptr)
+  : MessageLink(aChan)
+  , mTransport(nullptr)
+  , mIOLoop(nullptr)
+  , mExistingListener(nullptr)
 {
 }
 
 ProcessLink::~ProcessLink()
 {
-    mIOLoop = 0;
-    if (mTransport) {
-        mTransport->set_listener(0);
-        
-        // we only hold a weak ref to the transport, which is "owned"
-        // by GeckoChildProcess/GeckoThread
-        mTransport = 0;
-    }
+#ifdef DEBUG
+    mTransport = nullptr;
+    mIOLoop = nullptr;
+    mExistingListener = nullptr;
+#endif
 }
 
 void 
@@ -291,7 +293,8 @@ ProcessLink::OnEchoMessage(Message* msg)
 void
 ProcessLink::OnChannelOpened()
 {
-    mChan->AssertLinkThread();
+    AssertIOThread();
+
     {
         MonitorAutoLock lock(*mChan->mMonitor);
 
@@ -356,7 +359,11 @@ void
 ProcessLink::OnChannelError()
 {
     AssertIOThread();
+
     MonitorAutoLock lock(*mChan->mMonitor);
+
+    MOZ_ALWAYS_TRUE(this == mTransport->set_listener(mExistingListener));
+
     mChan->OnChannelErrorFromLink();
 }
 
@@ -368,6 +375,9 @@ ProcessLink::OnCloseChannel()
     mTransport->Close();
 
     MonitorAutoLock lock(*mChan->mMonitor);
+
+    MOZ_ALWAYS_TRUE(this == mTransport->set_listener(mExistingListener));
+
     mChan->mChannelState = ChannelClosed;
     mChan->mMonitor->Notify();
 }
diff --git a/ipc/glue/MessageLink.h b/ipc/glue/MessageLink.h
index 8203bc0d75fe..c069112f6c11 100644
--- a/ipc/glue/MessageLink.h
+++ b/ipc/glue/MessageLink.h
@@ -141,6 +141,14 @@ class ProcessLink
   public:
     explicit ProcessLink(MessageChannel *chan);
     virtual ~ProcessLink();
+
+    // The ProcessLink will register itself as the IPC::Channel::Listener on the
+    // transport passed here. If the transport already has a listener registered
+    // then a listener chain will be established (the ProcessLink listener
+    // methods will be called first and may call some methods on the original
+    // listener as well). Once the channel is closed (either via normal shutdown
+    // or a pipe error) the chain will be destroyed and the original listener
+    // will again be registered.
     void Open(Transport* aTransport, MessageLoop *aIOLoop, Side aSide);
     
     // Run on the I/O thread, only when using inter-process link.