Bug 1304883: Modify mscom::MainThreadInvoker and Win32 widget to use atomic boolean to flag pending APCs; r=jimm

MozReview-Commit-ID: 7fXoDkBEd2V

--HG--
extra : rebase_source : 1960f9bf8294bfea15209554dd7fdc0ce1df5dcc

ipc/mscom/MainThreadInvoker.cpp

@@ -14,8 +14,7 @@
 #include "mozilla/HangMonitor.h"
 #include "mozilla/RefPtr.h"
 #include "private/prpriv.h" // For PR_GetThreadID
-
-#include <winternl.h> // For NTSTATUS and NTAPI
+#include "WinUtils.h"
 
 namespace {
 
@@ -42,15 +41,12 @@ private:
   nsCOMPtr<nsIRunnable> mRunnable;
 };
 
-typedef NTSTATUS (NTAPI* NtTestAlertPtr)(VOID);
-
 } // anonymous namespace
 
 namespace mozilla {
 namespace mscom {
 
 HANDLE MainThreadInvoker::sMainThread = nullptr;
-StaticRefPtr<nsIRunnable> MainThreadInvoker::sAlertRunnable;
 
 /* static */ bool
 MainThreadInvoker::InitStatics()
@@ -67,25 +63,11 @@ MainThreadInvoker::InitStatics()
   }
   PRUint32 tid = ::PR_GetThreadID(mainPrThread);
   sMainThread = ::OpenThread(SYNCHRONIZE | THREAD_SET_CONTEXT, FALSE, tid);
-  if (!sMainThread) {
-    return false;
-  }
-  NtTestAlertPtr NtTestAlert =
-    reinterpret_cast<NtTestAlertPtr>(
-        ::GetProcAddress(::GetModuleHandleW(L"ntdll.dll"), "NtTestAlert"));
-  sAlertRunnable = ::NS_NewRunnableFunction([NtTestAlert]() -> void {
-    // We're using NtTestAlert() instead of SleepEx() so that the main thread
-    // never gives up its quantum if there are no APCs pending.
-    NtTestAlert();
-  }).take();
-  if (sAlertRunnable) {
-    ClearOnShutdown(&sAlertRunnable);
-  }
-  return !!sAlertRunnable;
+  return !!sMainThread;
 }
 
 MainThreadInvoker::MainThreadInvoker()
-  : mDoneEvent(::CreateEvent(nullptr, FALSE, FALSE, nullptr))
+  : mDoneEvent(::CreateEventW(nullptr, FALSE, FALSE, nullptr))
 {
   static const bool gotStatics = InitStatics();
   MOZ_ASSERT(gotStatics);
@@ -129,11 +111,11 @@ MainThreadInvoker::Invoke(already_AddRefed<nsIRunnable>&& aRunnable,
     wrappedRunnable->Release();
     return false;
   }
-  // We should enqueue a call to NtTestAlert() so that the main thread will
-  // check for APCs during event processing. If we omit this then the main
-  // thread will not check its APC queue until it is idle. Note that failing to
-  // dispatch this event is non-fatal, but it will delay execution of the APC.
-  Unused << NS_WARN_IF(NS_FAILED(NS_DispatchToMainThread(sAlertRunnable)));
+  // We should ensure a call to NtTestAlert() is made on the main thread so
+  // that the main thread will check for APCs during event processing. If we
+  // omit this then the main thread will not check its APC queue until it is
+  // idle.
+  widget::WinUtils::SetAPCPending();
   return WaitForCompletion(aTimeout);
 }
 

widget/windows/WinUtils.cpp

@@ -452,6 +452,11 @@ struct CoTaskMemFreePolicy
 
 SetThreadDpiAwarenessContextProc WinUtils::sSetThreadDpiAwarenessContext = NULL;
 EnableNonClientDpiScalingProc WinUtils::sEnableNonClientDpiScaling = NULL;
+#ifdef ACCESSIBILITY
+typedef NTSTATUS (NTAPI* NtTestAlertPtr)(VOID);
+static NtTestAlertPtr sNtTestAlert = nullptr;
+#endif
+
 
 /* static */
 void
@@ -486,6 +491,12 @@ WinUtils::Initialize()
         ::GetProcAddress(user32Dll, "SetThreadDpiAwarenessContext");
     }
   }
+
+#ifdef ACCESSIBILITY
+  sNtTestAlert = reinterpret_cast<NtTestAlertPtr>(
+      ::GetProcAddress(::GetModuleHandleW(L"ntdll.dll"), "NtTestAlert"));
+  MOZ_ASSERT(sNtTestAlert);
+#endif
 }
 
 // static
@@ -691,11 +702,31 @@ WinUtils::MonitorFromRect(const gfx::Rect& rect)
   return ::MonitorFromRect(&globalWindowBounds, MONITOR_DEFAULTTONEAREST);
 }
 
+#ifdef ACCESSIBILITY
+#ifndef STATUS_SUCCESS
+#define STATUS_SUCCESS ((NTSTATUS)0x00000000L)
+#endif
+
+static Atomic<bool> sAPCPending;
+
+/* static */
+void
+WinUtils::SetAPCPending()
+{
+  sAPCPending = true;
+}
+#endif // ACCESSIBILITY
+
 /* static */
 bool
 WinUtils::PeekMessage(LPMSG aMsg, HWND aWnd, UINT aFirstMessage,
                       UINT aLastMessage, UINT aOption)
 {
+#ifdef ACCESSIBILITY
+  if (NS_IsMainThread() && sAPCPending.exchange(false)) {
+    while (sNtTestAlert() != STATUS_SUCCESS) ;
+  }
+#endif
 #ifdef NS_ENABLE_TSF
   ITfMessagePump* msgPump = TSFTextStore::GetMessagePump();
   if (msgPump) {
@@ -764,14 +795,21 @@ WinUtils::WaitForMessage(DWORD aTimeoutMs)
     if (result == WAIT_TIMEOUT) {
       break;
     }
+#if defined(ACCESSIBILITY)
     if (result == WAIT_IO_COMPLETION) {
       if (NS_IsMainThread()) {
+        if (sAPCPending.exchange(false)) {
+          // Clear out any pending APCs
+          while (sNtTestAlert() != STATUS_SUCCESS) ;
+        }
         // We executed an APC that would have woken up the hang monitor. Since
-        // we're now going to sleep again, we should notify the hang monitor.
+        // there are no more APCs pending and we are now going to sleep again,
+        // we should notify the hang monitor.
         mozilla::HangMonitor::Suspend();
       }
       continue;
     }
+#endif // defined(ACCESSIBILITY)
 
     // Sent messages (via SendMessage and friends) are processed differently
     // than queued messages (via PostMessage); the destination window procedure

widget/windows/WinUtils.h

@@ -519,6 +519,10 @@ public:
    */
   static bool GetAppInitDLLs(nsAString& aOutput);
 
+#ifdef ACCESSIBILITY
+  static void SetAPCPending();
+#endif
+
 private:
   typedef HRESULT (WINAPI * SHCreateItemFromParsingNamePtr)(PCWSTR pszPath,
                                                             IBindCtx *pbc,