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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
* Windows widget support for event loop instrumentation.
* See toolkit/xre/EventTracer.cpp for more details.
#include <stdio.h>
#include <windows.h>
#include "mozilla/RefPtr.h"
#include "mozilla/WidgetTraceEvent.h"
#include "nsAppShellCID.h"
#include "nsComponentManagerUtils.h"
#include "nsCOMPtr.h"
#include "nsIAppShellService.h"
#include "nsIBaseWindow.h"
#include "nsIDocShell.h"
#include "nsISupportsImpl.h"
#include "nsIWidget.h"
#include "nsIAppWindow.h"
#include "nsServiceManagerUtils.h"
#include "nsThreadUtils.h"
#include "nsWindowDefs.h"
namespace {
// Used for signaling the background thread from the main thread.
HANDLE sEventHandle = nullptr;
// We need a runnable in order to find the hidden window on the main
// thread.
class HWNDGetter : public mozilla::Runnable {
HWNDGetter() : Runnable("HWNDGetter"), hidden_window_hwnd(nullptr) {}
HWND hidden_window_hwnd;
NS_IMETHOD Run() override {
// Jump through some hoops to locate the hidden window.
nsCOMPtr<nsIAppShellService> appShell(
nsCOMPtr<nsIAppWindow> hiddenWindow;
nsresult rv = appShell->GetHiddenWindow(getter_AddRefs(hiddenWindow));
if (NS_FAILED(rv)) {
return rv;
nsCOMPtr<nsIDocShell> docShell;
rv = hiddenWindow->GetDocShell(getter_AddRefs(docShell));
if (NS_FAILED(rv) || !docShell) {
return rv;
nsCOMPtr<nsIBaseWindow> baseWindow(do_QueryInterface(docShell));
if (!baseWindow) return NS_ERROR_FAILURE;
nsCOMPtr<nsIWidget> widget;
if (!widget) return NS_ERROR_FAILURE;
hidden_window_hwnd = (HWND)widget->GetNativeData(NS_NATIVE_WINDOW);
return NS_OK;
HWND GetHiddenWindowHWND() {
// Need to dispatch this to the main thread because plenty of
// the things it wants to access are main-thread-only.
RefPtr<HWNDGetter> getter = new HWNDGetter();
"GetHiddenWindowHWND"_ns, mozilla::GetMainThreadSerialEventTarget(),
return getter->hidden_window_hwnd;
} // namespace
namespace mozilla {
bool InitWidgetTracing() {
sEventHandle = CreateEventW(nullptr, FALSE, FALSE, nullptr);
return sEventHandle != nullptr;
void CleanUpWidgetTracing() {
sEventHandle = nullptr;
// This function is called from the main (UI) thread.
void SignalTracerThread() {
if (sEventHandle != nullptr) SetEvent(sEventHandle);
// This function is called from the background tracer thread.
bool FireAndWaitForTracerEvent() {
MOZ_ASSERT(sEventHandle, "Tracing not initialized!");
// First, try to find the hidden window.
static HWND hidden_window = nullptr;
if (hidden_window == nullptr) {
hidden_window = GetHiddenWindowHWND();
if (hidden_window == nullptr) return false;
// Post the tracer message into the hidden window's message queue,
// and then block until it's processed.
PostMessage(hidden_window, MOZ_WM_TRACE, 0, 0);
WaitForSingleObject(sEventHandle, INFINITE);
return true;
} // namespace mozilla