Bug 1800213 - Add a flag for creating nsThreads with a NONMAINUITHREAD MessageLoop. r=xpcom-reviewers,nika

Differential Revision: https://phabricator.services.mozilla.com/D166062

xpcom/tests/gtest/TestThreads.cpp

@@ -18,6 +18,11 @@
 #include "mozilla/SyncRunnable.h"
 #include "gtest/gtest.h"
 
+#ifdef XP_WIN
+#  include <windef.h>
+#  include <winuser.h>
+#endif
+
 using namespace mozilla;
 
 class nsRunner final : public Runnable {
@@ -377,3 +382,34 @@ TEST(Threads, UnregisteredShutdownTask)
 
   thread->Shutdown();
 }
+
+#if defined(XP_WIN) || !defined(DEBUG)
+TEST(Threads, OptionsIsUiThread)
+{
+  // On Windows, test that the isUiThread flag results in a GUI thread.
+  // In non-Windows non-debug builds, test that the isUiThread flag is ignored.
+
+  nsCOMPtr<nsIThread> thread;
+  nsIThreadManager::ThreadCreationOptions options;
+  options.isUiThread = true;
+  MOZ_ALWAYS_SUCCEEDS(NS_NewNamedThread(
+      "Testing Thread", getter_AddRefs(thread), nullptr, options));
+
+  bool isGuiThread = false;
+  auto syncRunnable =
+      MakeRefPtr<SyncRunnable>(NS_NewRunnableFunction(__func__, [&] {
+#  ifdef XP_WIN
+        isGuiThread = ::IsGUIThread(false);
+#  endif
+      }));
+  MOZ_ALWAYS_SUCCEEDS(syncRunnable->DispatchToThread(thread));
+
+  bool expectGuiThread = false;
+#  ifdef XP_WIN
+  expectGuiThread = true;
+#  endif
+  EXPECT_EQ(expectGuiThread, isGuiThread);
+
+  thread->Shutdown();
+}
+#endif

xpcom/threads/nsIThreadManager.idl

@@ -68,6 +68,10 @@ interface nsIThreadManager : nsISupports
     // and perform their own event dispatching internaly, such as thread pool
     // threads or the timer thread.
     bool blockDispatch = false;
+
+    // (Windows-only) Whether the thread should have a MessageLoop capable of
+    // processing native UI events. Defaults to false.
+    bool isUiThread = false;
   };
 %}
 

xpcom/threads/nsThread.cpp

@@ -378,7 +378,14 @@ void nsThread::ThreadFunc(void* aArg) {
 
   {
     // Scope for MessageLoop.
-    MessageLoop loop(MessageLoop::TYPE_MOZILLA_NONMAINTHREAD, self);
+    MessageLoop loop(
+#ifdef XP_WIN
+        self->mIsUiThread ? MessageLoop::TYPE_MOZILLA_NONMAINUITHREAD
+                          : MessageLoop::TYPE_MOZILLA_NONMAINTHREAD,
+#else
+        MessageLoop::TYPE_MOZILLA_NONMAINTHREAD,
+#endif
+        self);
 
     // Now, process incoming events...
     loop.Run();
@@ -560,13 +567,19 @@ nsThread::nsThread(NotNull<SynchronizedEventQueue*> aQueue,
       mPriority(PRIORITY_NORMAL),
       mIsMainThread(aMainThread == MAIN_THREAD),
       mUseHangMonitor(aMainThread == MAIN_THREAD),
+      mIsUiThread(aOptions.isUiThread),
       mIsAPoolThreadFree(nullptr),
       mCanInvokeJS(false),
 #ifdef EARLY_BETA_OR_EARLIER
       mLastWakeupCheckTime(TimeStamp::Now()),
 #endif
       mPerformanceCounterState(mNestedEventLoopDepth, mIsMainThread) {
+#ifndef XP_WIN
+  MOZ_ASSERT(!mIsUiThread, "Non-main UI threads are only supported on Windows");
+#endif
   if (mIsMainThread) {
+    MOZ_ASSERT(!mIsUiThread,
+               "Setting isUIThread is not supported for main threads");
     mozilla::TaskController::Get()->SetPerformanceCounterState(
         &mPerformanceCounterState);
   }
@@ -585,6 +598,7 @@ nsThread::nsThread()
       mPriority(PRIORITY_NORMAL),
       mIsMainThread(false),
       mUseHangMonitor(false),
+      mIsUiThread(false),
       mCanInvokeJS(false),
 #ifdef EARLY_BETA_OR_EARLIER
       mLastWakeupCheckTime(TimeStamp::Now()),

xpcom/threads/nsThread.h

@@ -315,6 +315,7 @@ class nsThread : public nsIThreadInternal,
 
   const bool mIsMainThread;
   bool mUseHangMonitor;
+  const bool mIsUiThread;
   mozilla::Atomic<bool, mozilla::Relaxed>* mIsAPoolThreadFree;
 
   // Set to true if this thread creates a JSRuntime.

xpcom/threads/nsThreadUtils.h

@@ -48,8 +48,9 @@ class nsIThread;
  *   The resulting nsIThread object.
  * @param aInitialEvent
  *   The initial event to run on this thread.  This parameter may be null.
- * @param aStackSize
- *   The size in bytes to reserve for the thread's stack.
+ * @param aOptions
+ *   Options used to configure thread creation.
+ *   Options are documented in nsIThreadManager.idl.
  *
  * @returns NS_ERROR_INVALID_ARG
  *   Indicates that the given name is not unique.