Bug 1431755 - Part 1: Add a variant of NS_GetCurrentThread that does not auto-create an nsIThread. r=froydnj

MozReview-Commit-ID: 9naTxaANX4u

--HG--
extra : rebase_source : 8ab21e09a6c154b90bd233212680fa93a96e0106

xpcom/threads/nsThreadManager.cpp

@@ -425,6 +425,12 @@ nsThreadManager::GetCurrentThread()
   return thread.get();  // reference held in TLS
 }
 
+bool
+nsThreadManager::IsNSThread() const
+{
+  return mInitialized && !!PR_GetThreadPrivate(mCurThreadIndex);
+}
+
 NS_IMETHODIMP
 nsThreadManager::NewThread(uint32_t aCreationFlags,
                            uint32_t aStackSize,

xpcom/threads/nsThreadManager.h

@@ -39,9 +39,13 @@ public:
   void UnregisterCurrentThread(nsThread& aThread);
 
   // Returns the current thread.  Returns null if OOM or if ThreadManager isn't
-  // initialized.
+  // initialized.  Creates the nsThread if one does not exist yet.
   nsThread* GetCurrentThread();
 
+  // Returns true iff the currently running thread has an nsThread associated
+  // with it (ie; whether this is a thread that we can dispatch runnables to).
+  bool IsNSThread() const;
+
   // CreateCurrentThread sets up an nsThread for the current thread. It uses the
   // event queue and main thread flags passed in. It should only be called once
   // for the current thread. After it returns, GetCurrentThread() will return

xpcom/threads/nsThreadUtils.cpp

@@ -530,6 +530,16 @@ NS_GetCurrentThread()
 {
   return nsThreadManager::get().GetCurrentThread();
 }
+
+
+nsIThread*
+NS_GetCurrentThreadNoCreate()
+{
+  if (nsThreadManager::get().IsNSThread()) {
+    return NS_GetCurrentThread();
+  }
+  return nullptr;
+}
 #endif
 
 // nsThreadPoolNaming

xpcom/threads/nsThreadUtils.h

@@ -74,7 +74,7 @@ NS_NewNamedThread(const char (&aName)[LEN],
 }
 
 /**
- * Get a reference to the current thread.
+ * Get a reference to the current thread, creating it if it does not exist yet.
  *
  * @param aResult
  *   The resulting nsIThread object.
@@ -368,12 +368,19 @@ do_GetMainThread()
 //-----------------------------------------------------------------------------
 
 #ifdef MOZILLA_INTERNAL_API
-// Fast access to the current thread.  Do not release the returned pointer!  If
-// you want to use this pointer from some other thread, then you will need to
-// AddRef it.  Otherwise, you should only consider this pointer valid from code
-// running on the current thread.
+// Fast access to the current thread.  Will create an nsIThread if one does not
+// exist already!  Do not release the returned pointer!  If you want to use this
+// pointer from some other thread, then you will need to AddRef it.  Otherwise,
+// you should only consider this pointer valid from code running on the current
+// thread.
 extern nsIThread* NS_GetCurrentThread();
 
+// Exactly the same as NS_GetCurrentThread, except it will not create an
+// nsThread if one does not exist yet. This is useful in cases where you have
+// code that runs on threads that may or may not not be driven by an nsThread
+// event loop, and wish to avoid inadvertently creating a superfluous nsThread.
+extern nsIThread* NS_GetCurrentThreadNoCreate();
+
 /**
  * Set the name of the current thread. Prefer this function over
  * PR_SetCurrentThreadName() if possible. The name will also be included in the