From a57b24343caf35091ed316072e897aa52f4d18bd Mon Sep 17 00:00:00 2001
From: Bill McCloskey <wmccloskey@mozilla.com>
Date: Thu, 8 May 2014 15:43:53 -0700
Subject: [PATCH] Bug 978892 - [e10s] Avoid racing when creating PJavaScript
 object (r=mrbkap)

---
 dom/ipc/ContentChild.cpp  | 2 ++
 dom/ipc/ContentParent.cpp | 4 ++--
 dom/ipc/PContent.ipdl     | 4 ++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/dom/ipc/ContentChild.cpp b/dom/ipc/ContentChild.cpp
index fe4546a6d2d..88bb4f95bf2 100644
--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -751,6 +751,8 @@ static void FirstIdle(void)
 mozilla::jsipc::PJavaScriptChild *
 ContentChild::AllocPJavaScriptChild()
 {
+    MOZ_ASSERT(!ManagedPJavaScriptChild().Length());
+
     nsCOMPtr<nsIJSRuntimeService> svc = do_GetService("@mozilla.org/js/xpc/RuntimeService;1");
     NS_ENSURE_TRUE(svc, nullptr);
 
diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 3978fd74126..ac9124820e3 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -1357,8 +1357,7 @@ ContentParent::GetCPOWManager()
     if (ManagedPJavaScriptParent().Length()) {
         return static_cast<JavaScriptParent*>(ManagedPJavaScriptParent()[0]);
     }
-    JavaScriptParent* actor = static_cast<JavaScriptParent*>(SendPJavaScriptConstructor());
-    return actor;
+    return nullptr;
 }
 
 TestShellParent*
@@ -2233,6 +2232,7 @@ ContentParent::RecvGetXPCOMProcessAttributes(bool* aIsOffline)
 mozilla::jsipc::PJavaScriptParent *
 ContentParent::AllocPJavaScriptParent()
 {
+    MOZ_ASSERT(!ManagedPJavaScriptParent().Length());
     mozilla::jsipc::JavaScriptParent *parent = new mozilla::jsipc::JavaScriptParent();
     if (!parent->init()) {
         delete parent;
diff --git a/dom/ipc/PContent.ipdl b/dom/ipc/PContent.ipdl
index 2306ccb7295..f6dc678ecff 100644
--- a/dom/ipc/PContent.ipdl
+++ b/dom/ipc/PContent.ipdl
@@ -317,8 +317,6 @@ both:
 
     async PBlob(BlobConstructorParams params);
 
-    async PJavaScript();
-
     PFileDescriptorSet(FileDescriptor fd);
 
 child:
@@ -425,6 +423,8 @@ parent:
     sync GetXPCOMProcessAttributes()
         returns (bool isOffline);
 
+    async PJavaScript();
+
     PDeviceStorageRequest(DeviceStorageParams params);
 
     PFileSystemRequest(FileSystemParams params);