Initial commit of sync engine code to browser/sync....

chrome/browser/sync/util/highres_timer-win32.h

+// Copyright (c) 2009 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.
+//
+// High resolution timer functions for use in Windows.
+
+#ifndef CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_WIN32_H_
+#define CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_WIN32_H_
+
+#include <windows.h>
+
+// A handy class for reliably measuring wall-clock time with decent resolution,
+// even on multi-processor machines and on laptops (where RDTSC potentially
+// returns different results on different processors and/or the RDTSC timer
+// clocks at different rates depending on the power state of the CPU,
+// respectively).
+class HighresTimer {
+ public:
+  // Captures the current start time.
+  HighresTimer();
+
+  // Captures the current tick, can be used to reset a timer for reuse.
+  void Start();
+
+  // Returns the elapsed ticks with full resolution.
+  ULONGLONG GetElapsedTicks() const;
+
+  // Returns the elapsed time in milliseconds, rounded to the nearest
+  // millisecond.
+  ULONGLONG GetElapsedMs() const;
+
+  // Returns the elapsed time in seconds, rounded to the nearest second.
+  ULONGLONG GetElapsedSec() const;
+
+  ULONGLONG start_ticks() const { return start_ticks_; }
+
+  // Returns timer frequency from cache, should be less
+  // overhead than ::QueryPerformanceFrequency.
+  static ULONGLONG GetTimerFrequency();
+  // Returns current ticks.
+  static ULONGLONG GetCurrentTicks();
+
+ private:
+  static void CollectPerfFreq();
+
+  // Captured start time.
+  ULONGLONG start_ticks_;
+
+  // Captured performance counter frequency.
+  static bool perf_freq_collected_;
+  static ULONGLONG perf_freq_;
+};
+
+inline HighresTimer::HighresTimer() {
+  Start();
+}
+
+inline void HighresTimer::Start() {
+  start_ticks_ = GetCurrentTicks();
+}
+
+inline ULONGLONG HighresTimer::GetTimerFrequency() {
+  if (!perf_freq_collected_)
+    CollectPerfFreq();
+  return perf_freq_;
+}
+
+inline ULONGLONG HighresTimer::GetCurrentTicks() {
+  LARGE_INTEGER ticks;
+  ::QueryPerformanceCounter(&ticks);
+  return ticks.QuadPart;
+}
+
+inline ULONGLONG HighresTimer::GetElapsedTicks() const {
+  return start_ticks_ - GetCurrentTicks();
+}
+
+#endif  // CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_WIN32_H_