Bug 1283609 - Part 3: Core changes, stop using nested event loop in B…

…ackgroundChild::GetOrCreateForCurrentThread(); r=billm

- BackgroundChild::GetOrCreateForCurrentThread(nsIIPCBackgroundChildCreateCallback* aCallback) emulates former asynchronous behavior

dom/ipc/ContentChild.h

@@ -7,6 +7,7 @@
 #ifndef mozilla_dom_ContentChild_h
 #define mozilla_dom_ContentChild_h
 
+#include "mozilla/Atomics.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/dom/ContentBridgeParent.h"
 #include "mozilla/dom/nsIContentChild.h"
@@ -755,7 +756,7 @@ class ContentChild final : public PContentChild
 
   nsClassHashtable<nsUint64HashKey, AnonymousTemporaryFileCallback> mPendingAnonymousTemporaryFiles;
 
-  bool mShuttingDown;
+  mozilla::Atomic<bool> mShuttingDown;
 
   DISALLOW_EVIL_CONSTRUCTORS(ContentChild);
 };

ipc/glue/BackgroundChild.h

@@ -34,15 +34,11 @@ class PBackgroundChild;
 // across threads. Each PBackgroundChild is unique and valid as long as its
 // designated thread lives.
 //
-// Creation of PBackground is asynchronous. GetForCurrentThread() will return
-// null until the sequence is complete.
+// Creation of PBackground is synchronous. GetOrCreateForCurrentThread will
+// create the actor if it doesn't exist yet. Thereafter (assuming success)
+// GetForCurrentThread() will return the same actor every time.
 // GetOrCreateForCurrentThread(nsIIPCBackgroundChildCreateCallback* aCallback)
-// will start the creation sequence and will call back via the passed interface
-// when completed. Thereafter (assuming success) GetForCurrentThread() will
-// return the same actor every time. GetOrCreateForCurrentThread() is like
-// GetOrCreateForCurrentThread(nsIIPCBackgroundChildCreateCallback* aCallback)
-// but it will return the actor synchronously (it will spin the event loop
-// until the creation sequence is complete).
+// emulates former asynchronous behavior and might be removed in future.
 //
 // CloseForCurrentThread() will close the current PBackground actor.  Subsequent
 // calls to GetForCurrentThread will return null.  CloseForCurrentThread() may