New test infrastructure for producing verbose logs in failing tests.

chrome/test/base/file_logger_win.h

+// 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.
+
+#ifndef CHROME_TEST_BASE_FILE_LOGGER_WIN_H_
+#define CHROME_TEST_BASE_FILE_LOGGER_WIN_H_
+#pragma once
+
+#include <guiddef.h>
+
+#include <ostream>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/win/event_trace_controller.h"
+
+class FilePath;
+
+// A file logger instance captures LOG messages emitted as events via Event
+// Tracing for Windows (ETW) and sends them to a file.  The contents of such a
+// file can be sent to an output stream sometime later.  Due to the nature of
+// event generation, only one instance of this class may be initialized at a
+// time.
+class FileLogger {

[erikwright (departed), 2012/03/02 20:47:59]

I wonder if you really need separate steps for constructing, Initializing,
Starting, Stopping, Uninitializing, and destroying?

[grt (UTC plus 2), 2012/03/02 21:22:43]

Yup, the collector does.  Initialize happens just before any tests run (it
doesn't happen, for example, if you just --gtest_list_tests).  Starting happens
at the beginning of a single test.  Stopping happens at the end of a single
tests.  There's a start/stop pair for each test.

[erikwright (departed), 2012/03/03 02:04:56]

OK. One thing to consider is whether you simplify the logic of this class by
merging initialization/construction and uninitialization/destruction. Then
replace member instances with scoped_ptr instances.

It's up to you, but I find that removing state is always positive.

[grt (UTC plus 2), 2012/03/03 02:31:59]

That's a good point.  I understand where you're coming from.  Since Initialize
does significant work (there's considerable overhead to doing the env var
thing), moving it into the ctor goes against the Google C++ style guide.

+ public:
+  FileLogger();
+  ~FileLogger();
+
+  // Initializes the instance to collect logs from the default set of providers:
+  // - chrome.exe
+  // - npchrome_frame.dll
+  // - this test binary.
+  // The system-wide variable CHROME_ETW_LOGGING=1 is added to the environment
+  // if it is not present.
+  void Initialize();
+
+  // Initializes the instance to collect logs from the given providers.
+  void Initialize(const GUID* const* provider_names, size_t provider_count);
+
+  // Removes the system-wide CHROME_ETW_LOGGING=1 variable from the environment
+  // if it was inserted in Initialize().
+  void Uninitialize();
+
+  // Starts capturing logs from all providers into |log_file|.  The common file
+  // extension for such files is .etl.
+  bool StartLogging(const FilePath& log_file);
+
+  // Stops capturing logs.
+  void StopLogging();
+
+  // Returns true if logs are being captured.
+  bool is_logging() const {
+    return controller_.session_name() && *controller_.session_name();
+  }
+
+  // Dumps all messages in |log_file|, which must have been produced by an
+  // instance of this class, to |out|.
+  static void DumpLogFile(const FilePath& log_file, std::ostream& out);
+
+ private:
+  bool EnableProviders();
+  void DisableProviders();
+
+  void ConfigureChromeEtwLogging();
+  void RevertChromeEtwLogging();
+
+  std::vector<GUID> provider_names_;
+  base::win::EtwTraceController controller_;
+
+  // True if the system-wide variable CHROME_ETW_LOGGING=1 was inserted into the
+  // environment.
+  bool added_chrome_etw_variable_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileLogger);
+};
+
+#endif  // CHROME_TEST_BASE_FILE_LOGGER_WIN_H_