base/timer/elapsed_timer.h

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_TIMER_ELAPSED_TIMER_H_
#define BASE_TIMER_ELAPSED_TIMER_H_

#include "base/base_export.h"
#include "base/time/time.h"

namespace base {

// A simple wrapper around TimeTicks::Now().
class BASE_EXPORT ElapsedTimer {
 public:
  ElapsedTimer();

  ElapsedTimer(const ElapsedTimer&) = default;
  ElapsedTimer& operator=(const ElapsedTimer&) = default;

  // Returns the time elapsed since object construction.
  TimeDelta Elapsed() const;

  // Returns the timestamp of the creation of this timer.
  TimeTicks start_time() const { return start_time_; }

 private:
  TimeTicks start_time_;
};

// A simple wrapper around ThreadTicks::Now().
class BASE_EXPORT ElapsedThreadTimer {
 public:
  ElapsedThreadTimer();

  ElapsedThreadTimer(const ElapsedThreadTimer&) = default;
  ElapsedThreadTimer& operator=(const ElapsedThreadTimer&) = default;

  // Returns the ThreadTicks time elapsed since object construction.
  // Only valid if |is_supported()| returns true, otherwise returns TimeDelta().
  TimeDelta Elapsed() const;

  bool is_supported() const { return is_supported_; }

 private:
  bool is_supported_;
  ThreadTicks begin_;
};

// A simple wrapper around LiveTicks::Now().
class BASE_EXPORT ElapsedLiveTimer {
 public:
  ElapsedLiveTimer();

  ElapsedLiveTimer(const ElapsedLiveTimer&) = default;
  ElapsedLiveTimer& operator=(const ElapsedLiveTimer&) = default;

  // Returns the time elapsed since object construction, not including time that
  // the system was suspended.
  TimeDelta Elapsed() const;

  // Returns the timestamp of the creation of this timer.
  LiveTicks start_time() const { return start_time_; }

 private:
  LiveTicks start_time_;
};

// Whenever there's a ScopedMockElapsedTimersForTest in scope, every
// ElapsedTimer (and variants like ElapsedThreadTimer and ElapsedLiveTimer) will
// always return kMockElapsedTime from Elapsed(). This is useful, for example,
// in unit tests that verify that their impl records timing histograms. It
// enables such tests to observe reliable timings.
class BASE_EXPORT ScopedMockElapsedTimersForTest {
 public:
  static constexpr TimeDelta kMockElapsedTime = Milliseconds(1337);

  // ScopedMockElapsedTimersForTest is not thread-safe (it must be instantiated
  // in a test before other threads begin using ElapsedTimers; and it must
  // conversely outlive any usage of ElapsedTimer in that test).
  ScopedMockElapsedTimersForTest();

  ScopedMockElapsedTimersForTest(const ScopedMockElapsedTimersForTest&) =
      delete;
  ScopedMockElapsedTimersForTest& operator=(
      const ScopedMockElapsedTimersForTest&) = delete;

  ~ScopedMockElapsedTimersForTest();
};

}  // namespace base

#endif  // BASE_TIMER_ELAPSED_TIMER_H_