base/win/event_trace_consumer_unittest.cc - chromium/src - Git at Google

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Unit tests for event trace consumer base class.
 #include "base/win/event_trace_consumer.h"

 #include <list>

 #include <objbase.h>

 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
 #include "base/process/process_handle.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/win/event_trace_controller.h"
 #include "base/win/event_trace_provider.h"
 #include "base/win/scoped_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"

 #include <initguid.h>  // NOLINT - has to be last

 namespace base {
 namespace win {

 namespace {

 typedef std::list<EVENT_TRACE> EventQueue;

 class TestConsumer: public EtwTraceConsumerBase<TestConsumer> {
  public:
   TestConsumer() {
     sank_event_.Set(::CreateEvent(NULL, TRUE, FALSE, NULL));
     ClearQueue();
   }

   ~TestConsumer() {
     ClearQueue();
     sank_event_.Close();
   }

   void ClearQueue() {
     for (EventQueue::const_iterator it(events_.begin()), end(events_.end());
          it != end; ++it) {
       delete[] reinterpret_cast<char*>(it->MofData);
     }

     events_.clear();
   }

   static void EnqueueEvent(EVENT_TRACE* event) {
     events_.push_back(*event);
     EVENT_TRACE& back = events_.back();

     if (event->MofData != NULL && event->MofLength != 0) {
       back.MofData = new char[event->MofLength];
       memcpy(back.MofData, event->MofData, event->MofLength);
     }
   }

   static void ProcessEvent(EVENT_TRACE* event) {
     EnqueueEvent(event);
     ::SetEvent(sank_event_.Get());
   }

   static ScopedHandle sank_event_;
   static EventQueue events_;

  private:
   DISALLOW_COPY_AND_ASSIGN(TestConsumer);
 };

 ScopedHandle TestConsumer::sank_event_;
 EventQueue TestConsumer::events_;

 class EtwTraceConsumerBaseTest: public testing::Test {
  public:
   EtwTraceConsumerBaseTest()
       : session_name_(StringPrintf(L"TestSession-%d", GetCurrentProcId())) {
   }

   void SetUp() override {
     // Cleanup any potentially dangling sessions.
     EtwTraceProperties ignore;
     EtwTraceController::Stop(session_name_.c_str(), &ignore);

     // Allocate a new GUID for each provider test.
     ASSERT_HRESULT_SUCCEEDED(::CoCreateGuid(&test_provider_));
   }

   void TearDown() override {
     // Cleanup any potentially dangling sessions.
     EtwTraceProperties ignore;
     EtwTraceController::Stop(session_name_.c_str(), &ignore);
   }

  protected:
   GUID test_provider_;
   std::wstring session_name_;
 };

 }  // namespace

 TEST_F(EtwTraceConsumerBaseTest, Initialize) {
   TestConsumer consumer_;
 }

 TEST_F(EtwTraceConsumerBaseTest, OpenRealtimeSucceedsWhenNoSession) {
   TestConsumer consumer_;
   ASSERT_HRESULT_SUCCEEDED(
       consumer_.OpenRealtimeSession(session_name_.c_str()));
 }

 TEST_F(EtwTraceConsumerBaseTest, ConsumerImmediateFailureWhenNoSession) {
   TestConsumer consumer_;
   ASSERT_HRESULT_SUCCEEDED(
       consumer_.OpenRealtimeSession(session_name_.c_str()));
   ASSERT_HRESULT_FAILED(consumer_.Consume());
 }

 namespace {

 class EtwTraceConsumerRealtimeTest: public EtwTraceConsumerBaseTest {
  public:
   void SetUp() override {
     EtwTraceConsumerBaseTest::SetUp();
     ASSERT_HRESULT_SUCCEEDED(
         consumer_.OpenRealtimeSession(session_name_.c_str()));
   }

   void TearDown() override {
     consumer_.Close();
     EtwTraceConsumerBaseTest::TearDown();
   }

   DWORD ConsumerThread() {
     ::SetEvent(consumer_ready_.Get());
     return consumer_.Consume();
   }

   static DWORD WINAPI ConsumerThreadMainProc(void* arg) {
     return reinterpret_cast<EtwTraceConsumerRealtimeTest*>(arg)->
         ConsumerThread();
   }

   HRESULT StartConsumerThread() {
     consumer_ready_.Set(::CreateEvent(NULL, TRUE, FALSE, NULL));
     EXPECT_TRUE(consumer_ready_.IsValid());
     consumer_thread_.Set(::CreateThread(NULL, 0, ConsumerThreadMainProc, this,
                                         0, NULL));
     if (consumer_thread_.Get() == NULL)
       return HRESULT_FROM_WIN32(::GetLastError());

     HANDLE events[] = { consumer_ready_.Get(), consumer_thread_.Get() };
     DWORD result =
         ::WaitForMultipleObjects(size(events), events, FALSE, INFINITE);
     switch (result) {
       case WAIT_OBJECT_0:
         // The event was set, the consumer_ is ready.
         return S_OK;
       case WAIT_OBJECT_0 + 1: {
           // The thread finished. This may race with the event, so check
           // explicitly for the event here, before concluding there's trouble.
           if (::WaitForSingleObject(consumer_ready_.Get(), 0) == WAIT_OBJECT_0)
             return S_OK;
           DWORD exit_code = 0;
           if (::GetExitCodeThread(consumer_thread_.Get(), &exit_code))
             return exit_code;
           return HRESULT_FROM_WIN32(::GetLastError());
         }
       default:
         return E_UNEXPECTED;
     }
   }

   // Waits for consumer_ thread to exit, and returns its exit code.
   HRESULT JoinConsumerThread() {
     if (::WaitForSingleObject(consumer_thread_.Get(), INFINITE) !=
         WAIT_OBJECT_0) {
       return HRESULT_FROM_WIN32(::GetLastError());
     }

     DWORD exit_code = 0;
     if (::GetExitCodeThread(consumer_thread_.Get(), &exit_code))
       return exit_code;

     return HRESULT_FROM_WIN32(::GetLastError());
   }

   TestConsumer consumer_;
   ScopedHandle consumer_ready_;
   ScopedHandle consumer_thread_;
 };

 }  // namespace

 TEST_F(EtwTraceConsumerRealtimeTest, ConsumerReturnsWhenSessionClosed) {
   EtwTraceController controller;
   if (controller.StartRealtimeSession(session_name_.c_str(), 100 * 1024) ==
       E_ACCESSDENIED) {
     VLOG(1) << "You must be an administrator to run this test on Vista";
     return;
   }

   // Start the consumer_.
   ASSERT_HRESULT_SUCCEEDED(StartConsumerThread());

   // Wait around for the consumer_ thread a bit.
   ASSERT_EQ(static_cast<DWORD>(WAIT_TIMEOUT),
             ::WaitForSingleObject(consumer_thread_.Get(), 50));
   ASSERT_HRESULT_SUCCEEDED(controller.Stop(NULL));

   // The consumer_ returns success on session stop.
   ASSERT_HRESULT_SUCCEEDED(JoinConsumerThread());
 }

 namespace {

 // {57E47923-A549-476f-86CA-503D57F59E62}
 DEFINE_GUID(
     kTestEventType,
     0x57e47923, 0xa549, 0x476f, 0x86, 0xca, 0x50, 0x3d, 0x57, 0xf5, 0x9e, 0x62);

 }  // namespace

 TEST_F(EtwTraceConsumerRealtimeTest, ConsumeEvent) {
   EtwTraceController controller;
   if (controller.StartRealtimeSession(session_name_.c_str(), 100 * 1024) ==
       E_ACCESSDENIED) {
     VLOG(1) << "You must be an administrator to run this test on Vista";
     return;
   }

   ASSERT_HRESULT_SUCCEEDED(controller.EnableProvider(
       test_provider_, TRACE_LEVEL_VERBOSE, 0xFFFFFFFF));

   EtwTraceProvider provider(test_provider_);
   ASSERT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Register());

   // Start the consumer_.
   ASSERT_HRESULT_SUCCEEDED(StartConsumerThread());
   ASSERT_EQ(0u, TestConsumer::events_.size());

   EtwMofEvent<1> event(kTestEventType, 1, TRACE_LEVEL_ERROR);
   EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Log(&event.header));
   EXPECT_EQ(WAIT_OBJECT_0,
             ::WaitForSingleObject(TestConsumer::sank_event_.Get(), INFINITE));
   ASSERT_HRESULT_SUCCEEDED(controller.Stop(NULL));
   ASSERT_HRESULT_SUCCEEDED(JoinConsumerThread());
   ASSERT_NE(0u, TestConsumer::events_.size());
 }

 namespace {

 // We run events through a file session to assert that
 // the content comes through.
 class EtwTraceConsumerDataTest: public EtwTraceConsumerBaseTest {
  public:
   EtwTraceConsumerDataTest() {
   }

   void SetUp() override {
     EtwTraceConsumerBaseTest::SetUp();

     EtwTraceProperties prop;
     EtwTraceController::Stop(session_name_.c_str(), &prop);

     // Create a temp dir for this test.
     ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
     // Construct a temp file name in our dir.
     temp_file_ = temp_dir_.GetPath().Append(FILE_PATH_LITERAL("test.etl"));
   }

   void TearDown() override {
     EXPECT_TRUE(DeleteFile(temp_file_, false));

     EtwTraceConsumerBaseTest::TearDown();
   }

   HRESULT LogEventToTempSession(PEVENT_TRACE_HEADER header) {
     EtwTraceController controller;

     // Set up a file session.
     HRESULT hr = controller.StartFileSession(session_name_.c_str(),
                                              as_wcstr(temp_file_.value()));
     if (FAILED(hr))
       return hr;

     // Enable our provider.
     EXPECT_HRESULT_SUCCEEDED(controller.EnableProvider(
         test_provider_, TRACE_LEVEL_VERBOSE, 0xFFFFFFFF));

     EtwTraceProvider provider(test_provider_);
     // Then register our provider, means we get a session handle immediately.
     EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Register());
     // Trace the event, it goes to the temp file.
     EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Log(header));
     EXPECT_HRESULT_SUCCEEDED(controller.DisableProvider(test_provider_));
     EXPECT_HRESULT_SUCCEEDED(provider.Unregister());
     EXPECT_HRESULT_SUCCEEDED(controller.Flush(NULL));
     EXPECT_HRESULT_SUCCEEDED(controller.Stop(NULL));

     return S_OK;
   }

   HRESULT ConsumeEventFromTempSession() {
     // Now consume the event(s).
     TestConsumer consumer_;
     HRESULT hr = consumer_.OpenFileSession(as_wcstr(temp_file_.value()));
     if (SUCCEEDED(hr))
       hr = consumer_.Consume();
     consumer_.Close();
     // And nab the result.
     events_.swap(TestConsumer::events_);
     return hr;
   }

   HRESULT RoundTripEvent(PEVENT_TRACE_HEADER header, PEVENT_TRACE* trace) {
     DeleteFile(temp_file_, false);

     HRESULT hr = LogEventToTempSession(header);
     if (SUCCEEDED(hr))
       hr = ConsumeEventFromTempSession();

     if (FAILED(hr))
       return hr;

     // We should now have the event in the queue.
     if (events_.empty())
       return E_FAIL;

     *trace = &events_.back();
     return S_OK;
   }

   EventQueue events_;
   ScopedTempDir temp_dir_;
   FilePath temp_file_;
 };

 }  // namespace


 TEST_F(EtwTraceConsumerDataTest, RoundTrip) {
   EtwMofEvent<1> event(kTestEventType, 1, TRACE_LEVEL_ERROR);

   static const char kData[] = "This is but test data";
   event.fields[0].DataPtr = reinterpret_cast<ULONG64>(kData);
   event.fields[0].Length = sizeof(kData);

   PEVENT_TRACE trace = NULL;
   HRESULT hr = RoundTripEvent(&event.header, &trace);
   if (hr == E_ACCESSDENIED) {
     VLOG(1) << "You must be an administrator to run this test on Vista";
     return;
   }
   ASSERT_HRESULT_SUCCEEDED(hr) << "RoundTripEvent failed";
   ASSERT_TRUE(trace != NULL);
   ASSERT_EQ(sizeof(kData), trace->MofLength);
   ASSERT_STREQ(kData, reinterpret_cast<const char*>(trace->MofData));
 }

 }  // namespace win
 }  // namespace base
	// Copyright (c) 2012 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.
	//
	// Unit tests for event trace consumer base class.
	#include "base/win/event_trace_consumer.h"

	#include <list>

	#include <objbase.h>

	#include "base/files/file_path.h"
	#include "base/files/file_util.h"
	#include "base/files/scoped_temp_dir.h"
	#include "base/logging.h"
	#include "base/process/process_handle.h"
	#include "base/stl_util.h"
	#include "base/strings/string_util.h"
	#include "base/strings/stringprintf.h"
	#include "base/win/event_trace_controller.h"
	#include "base/win/event_trace_provider.h"
	#include "base/win/scoped_handle.h"
	#include "testing/gtest/include/gtest/gtest.h"

	#include <initguid.h> // NOLINT - has to be last

	namespace base {
	namespace win {

	namespace {

	typedef std::list<EVENT_TRACE> EventQueue;

	class TestConsumer: public EtwTraceConsumerBase<TestConsumer> {
	public:
	TestConsumer() {
	sank_event_.Set(::CreateEvent(NULL, TRUE, FALSE, NULL));
	ClearQueue();
	}

	~TestConsumer() {
	ClearQueue();
	sank_event_.Close();
	}

	void ClearQueue() {
	for (EventQueue::const_iterator it(events_.begin()), end(events_.end());
	it != end; ++it) {
	delete[] reinterpret_cast<char*>(it->MofData);
	}

	events_.clear();
	}

	static void EnqueueEvent(EVENT_TRACE* event) {
	events_.push_back(*event);
	EVENT_TRACE& back = events_.back();

	if (event->MofData != NULL && event->MofLength != 0) {
	back.MofData = new char[event->MofLength];
	memcpy(back.MofData, event->MofData, event->MofLength);
	}
	}

	static void ProcessEvent(EVENT_TRACE* event) {
	EnqueueEvent(event);
	::SetEvent(sank_event_.Get());
	}

	static ScopedHandle sank_event_;
	static EventQueue events_;

	private:
	DISALLOW_COPY_AND_ASSIGN(TestConsumer);
	};

	ScopedHandle TestConsumer::sank_event_;
	EventQueue TestConsumer::events_;

	class EtwTraceConsumerBaseTest: public testing::Test {
	public:
	EtwTraceConsumerBaseTest()
	: session_name_(StringPrintf(L"TestSession-%d", GetCurrentProcId())) {
	}

	void SetUp() override {
	// Cleanup any potentially dangling sessions.
	EtwTraceProperties ignore;
	EtwTraceController::Stop(session_name_.c_str(), &ignore);

	// Allocate a new GUID for each provider test.
	ASSERT_HRESULT_SUCCEEDED(::CoCreateGuid(&test_provider_));
	}

	void TearDown() override {
	// Cleanup any potentially dangling sessions.
	EtwTraceProperties ignore;
	EtwTraceController::Stop(session_name_.c_str(), &ignore);
	}

	protected:
	GUID test_provider_;
	std::wstring session_name_;
	};

	} // namespace

	TEST_F(EtwTraceConsumerBaseTest, Initialize) {
	TestConsumer consumer_;
	}

	TEST_F(EtwTraceConsumerBaseTest, OpenRealtimeSucceedsWhenNoSession) {
	TestConsumer consumer_;
	ASSERT_HRESULT_SUCCEEDED(
	consumer_.OpenRealtimeSession(session_name_.c_str()));
	}

	TEST_F(EtwTraceConsumerBaseTest, ConsumerImmediateFailureWhenNoSession) {
	TestConsumer consumer_;
	ASSERT_HRESULT_SUCCEEDED(
	consumer_.OpenRealtimeSession(session_name_.c_str()));
	ASSERT_HRESULT_FAILED(consumer_.Consume());
	}

	namespace {

	class EtwTraceConsumerRealtimeTest: public EtwTraceConsumerBaseTest {
	public:
	void SetUp() override {
	EtwTraceConsumerBaseTest::SetUp();
	ASSERT_HRESULT_SUCCEEDED(
	consumer_.OpenRealtimeSession(session_name_.c_str()));
	}

	void TearDown() override {
	consumer_.Close();
	EtwTraceConsumerBaseTest::TearDown();
	}

	DWORD ConsumerThread() {
	::SetEvent(consumer_ready_.Get());
	return consumer_.Consume();
	}

	static DWORD WINAPI ConsumerThreadMainProc(void* arg) {
	return reinterpret_cast<EtwTraceConsumerRealtimeTest*>(arg)->
	ConsumerThread();
	}

	HRESULT StartConsumerThread() {
	consumer_ready_.Set(::CreateEvent(NULL, TRUE, FALSE, NULL));
	EXPECT_TRUE(consumer_ready_.IsValid());
	consumer_thread_.Set(::CreateThread(NULL, 0, ConsumerThreadMainProc, this,
	0, NULL));
	if (consumer_thread_.Get() == NULL)
	return HRESULT_FROM_WIN32(::GetLastError());

	HANDLE events[] = { consumer_ready_.Get(), consumer_thread_.Get() };
	DWORD result =
	::WaitForMultipleObjects(size(events), events, FALSE, INFINITE);
	switch (result) {
	case WAIT_OBJECT_0:
	// The event was set, the consumer_ is ready.
	return S_OK;
	case WAIT_OBJECT_0 + 1: {
	// The thread finished. This may race with the event, so check
	// explicitly for the event here, before concluding there's trouble.
	if (::WaitForSingleObject(consumer_ready_.Get(), 0) == WAIT_OBJECT_0)
	return S_OK;
	DWORD exit_code = 0;
	if (::GetExitCodeThread(consumer_thread_.Get(), &exit_code))
	return exit_code;
	return HRESULT_FROM_WIN32(::GetLastError());
	}
	default:
	return E_UNEXPECTED;
	}
	}

	// Waits for consumer_ thread to exit, and returns its exit code.
	HRESULT JoinConsumerThread() {
	if (::WaitForSingleObject(consumer_thread_.Get(), INFINITE) !=
	WAIT_OBJECT_0) {
	return HRESULT_FROM_WIN32(::GetLastError());
	}

	DWORD exit_code = 0;
	if (::GetExitCodeThread(consumer_thread_.Get(), &exit_code))
	return exit_code;

	return HRESULT_FROM_WIN32(::GetLastError());
	}

	TestConsumer consumer_;
	ScopedHandle consumer_ready_;
	ScopedHandle consumer_thread_;
	};

	} // namespace

	TEST_F(EtwTraceConsumerRealtimeTest, ConsumerReturnsWhenSessionClosed) {
	EtwTraceController controller;
	if (controller.StartRealtimeSession(session_name_.c_str(), 100 * 1024) ==
	E_ACCESSDENIED) {
	VLOG(1) << "You must be an administrator to run this test on Vista";
	return;
	}

	// Start the consumer_.
	ASSERT_HRESULT_SUCCEEDED(StartConsumerThread());

	// Wait around for the consumer_ thread a bit.
	ASSERT_EQ(static_cast<DWORD>(WAIT_TIMEOUT),
	::WaitForSingleObject(consumer_thread_.Get(), 50));
	ASSERT_HRESULT_SUCCEEDED(controller.Stop(NULL));

	// The consumer_ returns success on session stop.
	ASSERT_HRESULT_SUCCEEDED(JoinConsumerThread());
	}

	namespace {

	// {57E47923-A549-476f-86CA-503D57F59E62}
	DEFINE_GUID(
	kTestEventType,
	0x57e47923, 0xa549, 0x476f, 0x86, 0xca, 0x50, 0x3d, 0x57, 0xf5, 0x9e, 0x62);

	} // namespace

	TEST_F(EtwTraceConsumerRealtimeTest, ConsumeEvent) {
	EtwTraceController controller;
	if (controller.StartRealtimeSession(session_name_.c_str(), 100 * 1024) ==
	E_ACCESSDENIED) {
	VLOG(1) << "You must be an administrator to run this test on Vista";
	return;
	}

	ASSERT_HRESULT_SUCCEEDED(controller.EnableProvider(
	test_provider_, TRACE_LEVEL_VERBOSE, 0xFFFFFFFF));

	EtwTraceProvider provider(test_provider_);
	ASSERT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Register());

	// Start the consumer_.
	ASSERT_HRESULT_SUCCEEDED(StartConsumerThread());
	ASSERT_EQ(0u, TestConsumer::events_.size());

	EtwMofEvent<1> event(kTestEventType, 1, TRACE_LEVEL_ERROR);
	EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Log(&event.header));
	EXPECT_EQ(WAIT_OBJECT_0,
	::WaitForSingleObject(TestConsumer::sank_event_.Get(), INFINITE));
	ASSERT_HRESULT_SUCCEEDED(controller.Stop(NULL));
	ASSERT_HRESULT_SUCCEEDED(JoinConsumerThread());
	ASSERT_NE(0u, TestConsumer::events_.size());
	}

	namespace {

	// We run events through a file session to assert that
	// the content comes through.
	class EtwTraceConsumerDataTest: public EtwTraceConsumerBaseTest {
	public:
	EtwTraceConsumerDataTest() {
	}

	void SetUp() override {
	EtwTraceConsumerBaseTest::SetUp();

	EtwTraceProperties prop;
	EtwTraceController::Stop(session_name_.c_str(), &prop);

	// Create a temp dir for this test.
	ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
	// Construct a temp file name in our dir.
	temp_file_ = temp_dir_.GetPath().Append(FILE_PATH_LITERAL("test.etl"));
	}

	void TearDown() override {
	EXPECT_TRUE(DeleteFile(temp_file_, false));

	EtwTraceConsumerBaseTest::TearDown();
	}

	HRESULT LogEventToTempSession(PEVENT_TRACE_HEADER header) {
	EtwTraceController controller;

	// Set up a file session.
	HRESULT hr = controller.StartFileSession(session_name_.c_str(),
	as_wcstr(temp_file_.value()));
	if (FAILED(hr))
	return hr;

	// Enable our provider.
	EXPECT_HRESULT_SUCCEEDED(controller.EnableProvider(
	test_provider_, TRACE_LEVEL_VERBOSE, 0xFFFFFFFF));

	EtwTraceProvider provider(test_provider_);
	// Then register our provider, means we get a session handle immediately.
	EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Register());
	// Trace the event, it goes to the temp file.
	EXPECT_EQ(static_cast<DWORD>(ERROR_SUCCESS), provider.Log(header));
	EXPECT_HRESULT_SUCCEEDED(controller.DisableProvider(test_provider_));
	EXPECT_HRESULT_SUCCEEDED(provider.Unregister());
	EXPECT_HRESULT_SUCCEEDED(controller.Flush(NULL));
	EXPECT_HRESULT_SUCCEEDED(controller.Stop(NULL));

	return S_OK;
	}

	HRESULT ConsumeEventFromTempSession() {
	// Now consume the event(s).
	TestConsumer consumer_;
	HRESULT hr = consumer_.OpenFileSession(as_wcstr(temp_file_.value()));
	if (SUCCEEDED(hr))
	hr = consumer_.Consume();
	consumer_.Close();
	// And nab the result.
	events_.swap(TestConsumer::events_);
	return hr;
	}

	HRESULT RoundTripEvent(PEVENT_TRACE_HEADER header, PEVENT_TRACE* trace) {
	DeleteFile(temp_file_, false);

	HRESULT hr = LogEventToTempSession(header);
	if (SUCCEEDED(hr))
	hr = ConsumeEventFromTempSession();

	if (FAILED(hr))
	return hr;

	// We should now have the event in the queue.
	if (events_.empty())
	return E_FAIL;

	*trace = &events_.back();
	return S_OK;
	}

	EventQueue events_;
	ScopedTempDir temp_dir_;
	FilePath temp_file_;
	};

	} // namespace


	TEST_F(EtwTraceConsumerDataTest, RoundTrip) {
	EtwMofEvent<1> event(kTestEventType, 1, TRACE_LEVEL_ERROR);

	static const char kData[] = "This is but test data";
	event.fields[0].DataPtr = reinterpret_cast<ULONG64>(kData);
	event.fields[0].Length = sizeof(kData);

	PEVENT_TRACE trace = NULL;
	HRESULT hr = RoundTripEvent(&event.header, &trace);
	if (hr == E_ACCESSDENIED) {
	VLOG(1) << "You must be an administrator to run this test on Vista";
	return;
	}
	ASSERT_HRESULT_SUCCEEDED(hr) << "RoundTripEvent failed";
	ASSERT_TRUE(trace != NULL);
	ASSERT_EQ(sizeof(kData), trace->MofLength);
	ASSERT_STREQ(kData, reinterpret_cast<const char*>(trace->MofData));
	}

	} // namespace win
	} // namespace base