Don't deadlock on a child process for a CPOW (bug 905896, r=cjones).

dom/ipc/ContentParent.cpp

@@ -939,6 +939,10 @@ ContentParent::OnChannelConnected(int32_t pid)
         }
 #endif
     }
+
+    // Set a reply timeout. The only time the parent process will actually
+    // timeout is through urgent messages (which are used by CPOWs).
+    SetReplyTimeoutMs(Preferences::GetInt("dom.ipc.cpow.timeout", 3000));
 }
 
 void
@@ -2797,5 +2801,14 @@ ContentParent::RecvKeywordToURI(const nsCString& aKeyword, OptionalInputStreamPa
   return true;
 }
 
+bool
+ContentParent::ShouldContinueFromReplyTimeout()
+{
+  // The only time ContentParent sends blocking messages is for CPOWs, so
+  // timeouts should only ever occur in electrolysis-enabled sessions.
+  MOZ_ASSERT(Preferences::GetBool("browser.tabs.remote", false));
+  return false;
+}
+
 } // namespace dom
 } // namespace mozilla

dom/ipc/ContentParent.h

@@ -180,6 +180,8 @@ protected:
     void OnChannelConnected(int32_t pid) MOZ_OVERRIDE;
     virtual void ActorDestroy(ActorDestroyReason why);
 
+    bool ShouldContinueFromReplyTimeout() MOZ_OVERRIDE;
+
 private:
     static nsDataHashtable<nsStringHashKey, ContentParent*> *sAppContentParents;
     static nsTArray<ContentParent*>* sNonAppContentParents;

ipc/glue/SyncChannel.cpp

@@ -322,6 +322,15 @@ SyncChannel::ShouldContinueFromTimeout()
         cont = static_cast<SyncListener*>(mListener.get())->OnReplyTimeout();
     }
 
+    static enum { UNKNOWN, NOT_DEBUGGING, DEBUGGING } sDebuggingChildren = UNKNOWN;
+
+    if (sDebuggingChildren == UNKNOWN) {
+        sDebuggingChildren = getenv("MOZ_DEBUG_CHILD_PROCESS") ? DEBUGGING : NOT_DEBUGGING;
+    }
+    if (sDebuggingChildren == DEBUGGING) {
+        return true;
+    }
+
     if (!cont) {
         // NB: there's a sublety here.  If parents were allowed to
         // send sync messages to children, then it would be possible

ipc/ipdl/test/cxx/PTestDataStructures.ipdl

@@ -1,6 +1,8 @@
 include protocol PTestDataStructuresSub;
 include PTestDataStructuresCommon;
 
+include "mozilla/GfxMessageUtils.h";
+
 namespace mozilla {
 namespace _ipdltest {
 

ipc/ipdl/test/cxx/PTestUrgency.ipdl

@@ -9,12 +9,14 @@ parent:
     sync Test3() returns (uint32_t result);
     sync Test4_Begin();
     sync Test4_NestedSync();
+    sync FinalTest_Begin();
 
 child:
     async Start();
     urgent Reply1() returns (uint32_t result);
     urgent Reply2() returns (uint32_t result);
     urgent Test4_Reenter();
+    urgent FinalTest_Hang();
 };
 
 } // namespace _ipdltest

ipc/ipdl/test/cxx/TestUrgency.cpp

@@ -3,6 +3,13 @@
 #include "IPDLUnitTests.h"      // fail etc.
 #include <unistd.h>
 
+template<>
+struct RunnableMethodTraits<mozilla::_ipdltest::TestUrgencyParent>
+{
+    static void RetainCallee(mozilla::_ipdltest::TestUrgencyParent* obj) { }
+    static void ReleaseCallee(mozilla::_ipdltest::TestUrgencyParent* obj) { }
+};
+
 namespace mozilla {
 namespace _ipdltest {
 
@@ -74,6 +81,21 @@ TestUrgencyParent::RecvTest4_NestedSync()
   return false;
 }
 
+bool
+TestUrgencyParent::RecvFinalTest_Begin()
+{
+  SetReplyTimeoutMs(2000);
+  if (CallFinalTest_Hang())
+    fail("should have failed due to timeout");
+  if (!GetIPCChannel()->Unsound_IsClosed())
+    fail("channel should have closed");
+
+  MessageLoop::current()->PostTask(
+      FROM_HERE,
+      NewRunnableMethod(this, &TestUrgencyParent::Close));
+  return false;
+}
+
 //-----------------------------------------------------------------------------
 // child
 
@@ -115,6 +137,10 @@ TestUrgencyChild::RecvStart()
   if (!SendTest4_Begin())
     fail("calling SendTest4_Begin");
 
+  // This must be the last test, since the child process may die.
+  if (SendFinalTest_Begin())
+    fail("Final test should not have succeeded");
+
   Close();
 
   return true;
@@ -153,6 +179,13 @@ TestUrgencyChild::AnswerTest4_Reenter()
   return true;
 }
 
+bool
+TestUrgencyChild::AnswerFinalTest_Hang()
+{
+  sleep(10);
+  return true;
+}
+
 TestUrgencyChild::TestUrgencyChild()
   : test_(0)
 {

ipc/ipdl/test/cxx/TestUrgency.h

@@ -27,14 +27,20 @@ public:
     bool RecvTest3(uint32_t *value);
     bool RecvTest4_Begin();
     bool RecvTest4_NestedSync();
+    bool RecvFinalTest_Begin();
 
+    bool ShouldContinueFromReplyTimeout() MOZ_OVERRIDE
+    {
+      return false;
+    }
     virtual void ActorDestroy(ActorDestroyReason why) MOZ_OVERRIDE
     {
-        if (NormalShutdown != why)
+        if (AbnormalShutdown != why)
             fail("unexpected destruction!");  
         passed("ok");
         QuitParent();
     }
+
 private:
     bool inreply_;
 };
@@ -51,10 +57,11 @@ public:
     bool AnswerReply1(uint32_t *reply);
     bool AnswerReply2(uint32_t *reply);
     bool AnswerTest4_Reenter();
+    bool AnswerFinalTest_Hang();
 
     virtual void ActorDestroy(ActorDestroyReason why) MOZ_OVERRIDE
     {
-        if (NormalShutdown != why)
+        if (AbnormalShutdown != why)
             fail("unexpected destruction!");
         QuitChild();
     }

js/ipc/JavaScriptParent.cpp

@@ -594,7 +594,7 @@ JavaScriptParent::unwrap(JSContext *cx, ObjectId objId)
 bool
 JavaScriptParent::ipcfail(JSContext *cx)
 {
-    JS_ReportError(cx, "catastrophic IPC failure");
+    JS_ReportError(cx, "child process crashed or timedout");
     return false;
 }