Bug 1602646 - Remove vestigial references to cooperative scheduling r=froydnj

GetCurrentPhysicalThread and GetCurrentVirtualThread are, in practice,
identical, as the TLS override that GetCurrentVirtualThread depends on
is never actually set. This simply removes that and renames some things/
deletes some comments.

Rebased across https://hg.mozilla.org/mozilla-central/rev/3f0b4e206853
by Karl Tomlinson <karlt+@karlt.net>.

Differential Revision: https://phabricator.services.mozilla.com/D41247

--HG--
extra : moz-landing-system : lando

dom/canvas/ImageBitmap.cpp

@@ -1083,11 +1083,11 @@ class CreateImageBitmapFromBlob final : public CancelableRunnable,
         mCropRect(aCropRect),
         mOriginalCropRect(aCropRect),
         mMainThreadEventTarget(aMainThreadEventTarget),
-        mThread(GetCurrentVirtualThread()) {}
+        mThread(PR_GetCurrentThread()) {}
 
   virtual ~CreateImageBitmapFromBlob() {}
 
-  bool IsCurrentThread() const { return mThread == GetCurrentVirtualThread(); }
+  bool IsCurrentThread() const { return mThread == PR_GetCurrentThread(); }
 
   // Called on the owning thread.
   nsresult StartMimeTypeAndDecodeAndCropBlob();

dom/indexedDB/ActorsParent.cpp

@@ -5146,7 +5146,7 @@ struct ConnectionPool::DatabaseInfo final {
 
   void AssertIsOnConnectionThread() const {
     MOZ_ASSERT(mDEBUGConnectionThread);
-    MOZ_ASSERT(GetCurrentPhysicalThread() == mDEBUGConnectionThread);
+    MOZ_ASSERT(PR_GetCurrentThread() == mDEBUGConnectionThread);
   }
 
   uint64_t TotalTransactionCount() const {
@@ -11208,7 +11208,7 @@ nsresult ConnectionPool::GetOrCreateConnection(
                    NS_ConvertUTF16toUTF8(aDatabase->FilePath()).get()));
 
 #ifdef DEBUG
-    dbInfo->mDEBUGConnectionThread = GetCurrentPhysicalThread();
+    dbInfo->mDEBUGConnectionThread = PR_GetCurrentThread();
 #endif
   }
 

dom/media/MediaManager.cpp

@@ -4032,7 +4032,7 @@ void SourceListener::Activate(RefPtr<MediaDevice> aAudioDevice,
   MOZ_ASSERT(!mStopped, "Cannot activate stopped source listener");
   MOZ_ASSERT(!Activated(), "Already activated");
 
-  mMainThreadCheck = GetCurrentVirtualThread();
+  mMainThreadCheck = PR_GetCurrentThread();
   if (aAudioDevice) {
     bool offWhileDisabled =
         aAudioDevice->GetMediaSource() == MediaSourceEnum::Microphone &&

ipc/glue/MessageChannel.cpp

@@ -834,7 +834,7 @@ bool MessageChannel::Open(Transport* aTransport, MessageLoop* aIOLoop,
 
   mMonitor = new RefCountedMonitor();
   mWorkerLoop = MessageLoop::current();
-  mWorkerThread = GetCurrentVirtualThread();
+  mWorkerThread = PR_GetCurrentThread();
   mWorkerLoop->AddDestructionObserver(this);
   mListener->OnIPCChannelOpened();
 
@@ -915,7 +915,7 @@ void MessageChannel::OnOpenAsSlave(MessageChannel* aTargetChan, Side aSide) {
 void MessageChannel::CommonThreadOpenInit(MessageChannel* aTargetChan,
                                           Side aSide) {
   mWorkerLoop = MessageLoop::current();
-  mWorkerThread = GetCurrentVirtualThread();
+  mWorkerThread = PR_GetCurrentThread();
   mWorkerLoop->AddDestructionObserver(this);
   mListener->OnIPCChannelOpened();
 

ipc/glue/MessageChannel.h

@@ -551,7 +551,7 @@ class MessageChannel : HasResultCodes, MessageLoop::DestructionObserver {
   // Can be run on either thread
   void AssertWorkerThread() const {
     MOZ_ASSERT(mWorkerThread, "Channel hasn't been opened yet");
-    MOZ_RELEASE_ASSERT(mWorkerThread == GetCurrentVirtualThread(),
+    MOZ_RELEASE_ASSERT(mWorkerThread == PR_GetCurrentThread(),
                        "not on worker thread!");
   }
 
@@ -569,7 +569,7 @@ class MessageChannel : HasResultCodes, MessageLoop::DestructionObserver {
     // If we aren't a same-thread channel, our "link" thread is _not_ our
     // worker thread!
     MOZ_ASSERT(mWorkerThread, "Channel hasn't been opened yet");
-    MOZ_RELEASE_ASSERT(mWorkerThread != GetCurrentVirtualThread(),
+    MOZ_RELEASE_ASSERT(mWorkerThread != PR_GetCurrentThread(),
                        "on worker thread but should not be!");
   }
 

tools/fuzzing/ipc/ProtocolFuzzer.cpp

@@ -24,7 +24,7 @@ mozilla::dom::ContentParent* ProtocolFuzzerHelper::CreateContentParent(
     mozilla::dom::ContentParent* aOpener, const nsAString& aRemoteType) {
   auto* cp = new mozilla::dom::ContentParent(aOpener, aRemoteType);
   // TODO: this duplicates MessageChannel::Open
-  cp->GetIPCChannel()->mWorkerThread = GetCurrentVirtualThread();
+  cp->GetIPCChannel()->mWorkerThread = PR_GetCurrentThread();
   cp->GetIPCChannel()->mMonitor = new RefCountedMonitor();
   return cp;
 }

xpcom/base/nsISupportsImpl.cpp

@@ -32,7 +32,7 @@ nsresult NS_FASTCALL NS_TableDrivenQI(void* aThis, REFNSIID aIID,
 }
 
 #ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED
-nsAutoOwningThread::nsAutoOwningThread() : mThread(GetCurrentVirtualThread()) {}
+nsAutoOwningThread::nsAutoOwningThread() : mThread(PR_GetCurrentThread()) {}
 
 void nsAutoOwningThread::AssertCurrentThreadOwnsMe(const char* msg) const {
   if (MOZ_UNLIKELY(!IsCurrentThread())) {
@@ -42,6 +42,6 @@ void nsAutoOwningThread::AssertCurrentThreadOwnsMe(const char* msg) const {
 }
 
 bool nsAutoOwningThread::IsCurrentThread() const {
-  return mThread == GetCurrentVirtualThread();
+  return mThread == PR_GetCurrentThread();
 }
 #endif

xpcom/threads/TaskQueue.cpp

@@ -172,7 +172,7 @@ bool TaskQueue::IsEmpty() {
 }
 
 bool TaskQueue::IsCurrentThreadIn() const {
-  bool in = mRunningThread == GetCurrentPhysicalThread();
+  bool in = mRunningThread == PR_GetCurrentThread();
   return in;
 }
 

xpcom/threads/TaskQueue.h

@@ -162,13 +162,13 @@ class TaskQueue : public AbstractThread {
       sCurrentThreadTLS.set(aQueue);
 
       MOZ_ASSERT(mQueue->mRunningThread == nullptr);
-      mQueue->mRunningThread = GetCurrentPhysicalThread();
+      mQueue->mRunningThread = PR_GetCurrentThread();
     }
 
     ~AutoTaskGuard() {
       DrainDirectTasks();
 
-      MOZ_ASSERT(mQueue->mRunningThread == GetCurrentPhysicalThread());
+      MOZ_ASSERT(mQueue->mRunningThread == PR_GetCurrentThread());
       mQueue->mRunningThread = nullptr;
 
       sCurrentThreadTLS.set(mLastCurrentThread);

xpcom/threads/ThreadEventTarget.cpp

@@ -89,14 +89,12 @@ NS_IMPL_ISUPPORTS_INHERITED(DelayedRunnable, Runnable, nsITimerCallback)
 ThreadEventTarget::ThreadEventTarget(ThreadTargetSink* aSink,
                                      bool aIsMainThread)
     : mSink(aSink), mIsMainThread(aIsMainThread) {
-  mVirtualThread = GetCurrentVirtualThread();
+  mThread = PR_GetCurrentThread();
 }
 
-void ThreadEventTarget::SetCurrentThread() {
-  mVirtualThread = GetCurrentVirtualThread();
-}
+void ThreadEventTarget::SetCurrentThread() { mThread = PR_GetCurrentThread(); }
 
-void ThreadEventTarget::ClearCurrentThread() { mVirtualThread = nullptr; }
+void ThreadEventTarget::ClearCurrentThread() { mThread = nullptr; }
 
 NS_IMPL_ISUPPORTS(ThreadEventTarget, nsIEventTarget, nsISerialEventTarget)
 
@@ -187,6 +185,6 @@ ThreadEventTarget::IsOnCurrentThread(bool* aIsOnCurrentThread) {
 
 NS_IMETHODIMP_(bool)
 ThreadEventTarget::IsOnCurrentThreadInfallible() {
-  // Rely on mVirtualThread being correct.
+  // Rely on mThread being correct.
   MOZ_CRASH("IsOnCurrentThreadInfallible should never be called on nsIThread");
 }

xpcom/threads/nsIEventTarget.idl

@@ -79,8 +79,8 @@ interface nsIEventTarget : nsISupports
    *
    * The infallible version of IsOnCurrentThread() is optimized to avoid a
    * virtual call for non-thread event targets. Thread targets should set
-   * mVirtualThread to their virtual PRThread. Non-thread targets should leave
-   * mVirtualThread null and implement IsOnCurrentThreadInfallible() to
+   * mThread to their virtual PRThread. Non-thread targets should leave
+   * mThread null and implement IsOnCurrentThreadInfallible() to
    * return the correct answer.
    *
    * The fallible version of IsOnCurrentThread may return errors, such as during
@@ -91,13 +91,13 @@ interface nsIEventTarget : nsISupports
   %{C++
 public:
   // Infallible. Defined in nsThreadUtils.cpp. Delegates to
-  // IsOnCurrentThreadInfallible when mVirtualThread is null.
+  // IsOnCurrentThreadInfallible when mThread is null.
   bool IsOnCurrentThread();
 
 protected:
-  mozilla::Atomic<PRThread*> mVirtualThread;
+  mozilla::Atomic<PRThread*> mThread;
 
-  nsIEventTarget() : mVirtualThread(nullptr) {}
+  nsIEventTarget() : mThread(nullptr) {}
   %}
   // Note that this method is protected.  We define it through IDL, rather than
   // in a %{C++ block, to ensure that the correct method indices are recorded

xpcom/threads/nsThread.cpp

@@ -420,7 +420,6 @@ void nsThread::ThreadFunc(void* aArg) {
   MOZ_ASSERT(self->mEvents);
 
   self->mThread = PR_GetCurrentThread();
-  self->mVirtualThread = GetCurrentVirtualThread();
   self->mEventTarget->SetCurrentThread();
   SetupCurrentThreadForChaosMode();
 
@@ -508,7 +507,6 @@ void nsThread::ThreadFunc(void* aArg) {
 
   // The PRThread will be deleted in PR_JoinThread(), so clear references.
   self->mThread = nullptr;
-  self->mVirtualThread = nullptr;
   self->mEventTarget->ClearCurrentThread();
   NS_RELEASE(self);
 }
@@ -600,7 +598,6 @@ nsThread::nsThread(NotNull<SynchronizedEventQueue*> aQueue,
           new ThreadEventTarget(mEvents.get(), aMainThread == MAIN_THREAD)),
       mShutdownContext(nullptr),
       mScriptObserver(nullptr),
-      mThread(nullptr),
       mStackSize(aStackSize),
       mNestedEventLoopDepth(0),
       mCurrentEventLoopDepth(MaxValue<uint32_t>::value),
@@ -624,7 +621,6 @@ nsThread::nsThread()
       mEventTarget(nullptr),
       mShutdownContext(nullptr),
       mScriptObserver(nullptr),
-      mThread(nullptr),
       mStackSize(0),
       mNestedEventLoopDepth(0),
       mCurrentEventLoopDepth(MaxValue<uint32_t>::value),
@@ -699,7 +695,6 @@ nsresult nsThread::Init(const nsACString& aName) {
 
 nsresult nsThread::InitCurrentThread() {
   mThread = PR_GetCurrentThread();
-  mVirtualThread = GetCurrentVirtualThread();
   SetupCurrentThreadForChaosMode();
   InitCommon();
 
@@ -764,13 +759,13 @@ nsThread::IsOnCurrentThread(bool* aResult) {
   if (mEventTarget) {
     return mEventTarget->IsOnCurrentThread(aResult);
   }
-  *aResult = GetCurrentVirtualThread() == mVirtualThread;
+  *aResult = PR_GetCurrentThread() == mThread;
   return NS_OK;
 }
 
 NS_IMETHODIMP_(bool)
 nsThread::IsOnCurrentThreadInfallible() {
-  // This method is only going to be called if `mVirtualThread` is null, which
+  // This method is only going to be called if `mThread` is null, which
   // only happens when the thread has exited the event loop.  Therefore, when
   // we are called, we can never be on this thread.
   return false;

xpcom/threads/nsThread.h

@@ -214,7 +214,6 @@ class nsThread : public nsIThreadInternal,
 
   mozilla::CycleCollectedJSContext* mScriptObserver;
 
-  PRThread* mThread;
   void* mStackBase = nullptr;
   uint32_t mStackSize;
   uint32_t mThreadId;

xpcom/threads/nsThreadManager.cpp

@@ -33,7 +33,6 @@
 using namespace mozilla;
 
 static MOZ_THREAD_LOCAL(bool) sTLSIsMainThread;
-static MOZ_THREAD_LOCAL(PRThread*) gTlsCurrentVirtualThread;
 
 bool NS_IsMainThreadTLSInitialized() { return sTLSIsMainThread.initialized(); }
 
@@ -160,18 +159,6 @@ void NS_SetMainThread() {
   MOZ_ASSERT(NS_IsMainThread());
 }
 
-void NS_SetMainThread(PRThread* aVirtualThread) {
-  MOZ_ASSERT(!gTlsCurrentVirtualThread.get());
-  gTlsCurrentVirtualThread.set(aVirtualThread);
-  NS_SetMainThread();
-}
-
-void NS_UnsetMainThread() {
-  sTLSIsMainThread.set(false);
-  MOZ_ASSERT(!NS_IsMainThread());
-  gTlsCurrentVirtualThread.set(nullptr);
-}
-
 #ifdef DEBUG
 
 namespace mozilla {
@@ -315,10 +302,6 @@ nsresult nsThreadManager::Init() {
     return NS_OK;
   }
 
-  if (!gTlsCurrentVirtualThread.init()) {
-    return NS_ERROR_UNEXPECTED;
-  }
-
   if (PR_NewThreadPrivateIndex(&mCurThreadIndex, ReleaseThread) == PR_FAILURE) {
     return NS_ERROR_FAILURE;
   }
@@ -733,20 +716,3 @@ nsThreadManager::IdleDispatchToMainThread(nsIRunnable* aEvent,
   return NS_DispatchToThreadQueue(event.forget(), mMainThread,
                                   EventQueuePriority::Idle);
 }
-
-namespace mozilla {
-
-PRThread* GetCurrentVirtualThread() {
-  // We call GetCurrentVirtualThread very early in startup, before the TLS is
-  // initialized. Make sure we don't assert in that case.
-  if (gTlsCurrentVirtualThread.initialized()) {
-    if (gTlsCurrentVirtualThread.get()) {
-      return gTlsCurrentVirtualThread.get();
-    }
-  }
-  return PR_GetCurrentThread();
-}
-
-PRThread* GetCurrentPhysicalThread() { return PR_GetCurrentThread(); }
-
-}  // namespace mozilla

xpcom/threads/nsThreadUtils.cpp

@@ -614,8 +614,8 @@ size_t GetNumberOfProcessors() {
 }  // namespace mozilla
 
 bool nsIEventTarget::IsOnCurrentThread() {
-  if (mVirtualThread) {
-    return mVirtualThread == GetCurrentVirtualThread();
+  if (mThread) {
+    return mThread == PR_GetCurrentThread();
   }
   return IsOnCurrentThreadInfallible();
 }

xpcom/threads/nsThreadUtils.h

@@ -1709,50 +1709,6 @@ extern nsresult NS_DispatchBackgroundTask(
 
 namespace mozilla {
 
-/**
- * Cooperative thread scheduling is governed by two rules:
- * - Only one thread in the pool of cooperatively scheduled threads runs at a
- *   time.
- * - Thread switching happens at well-understood safe points.
- *
- * In some cases we may want to treat all the threads in a cooperative pool as a
- * single thread, while other parts of the code may want to view them as
- * separate threads. GetCurrentVirtualThread() will return the same value for
- * all threads in a cooperative thread pool. GetCurrentPhysicalThread will
- * return a different value for each thread in the pool.
- *
- * Thread safety assertions are a concrete example where GetCurrentVirtualThread
- * should be used. An object may want to assert that it only can be used on the
- * thread that created it. Such assertions would normally prevent the object
- * from being used on different cooperative threads. However, the object might
- * really only care that it's used atomically. Cooperative scheduling guarantees
- * that it will be (assuming we don't yield in the middle of modifying the
- * object). So we can weaken the assertion to compare the virtual thread the
- * object was created on to the virtual thread on which it's being used. This
- * assertion allows the object to be used across threads in a cooperative thread
- * pool while preventing accesses across preemptively scheduled threads (which
- * would be unsafe).
- */
-
-// Returns the PRThread on which this code is running.
-PRThread* GetCurrentPhysicalThread();
-
-// Returns a "virtual" PRThread that should only be used for comparison with
-// other calls to GetCurrentVirtualThread. Two threads in the same cooperative
-// thread pool will return the same virtual thread. Threads that are not
-// cooperatively scheduled will have their own unique virtual PRThread (which
-// will be equal to their physical PRThread).
-//
-// The return value of GetCurrentVirtualThread() is guaranteed not to change
-// throughout the lifetime of a thread.
-//
-// Note that the original main thread (the first one created in the process) is
-// considered as part of the pool of cooperative threads, so the return value of
-// GetCurrentVirtualThread() for this thread (throughout its lifetime, even
-// during shutdown) is the same as the return value from any other thread in the
-// cooperative pool.
-PRThread* GetCurrentVirtualThread();
-
 // These functions return event targets that can be used to dispatch to the
 // current or main thread. They can also be used to test if you're on those
 // threads (via IsOnCurrentThread). These functions should be used in preference