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

chrome/browser/sync/util/highres_timer-linux.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 Linux.
+
+#ifndef CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_LINUX_H_
+#define CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_LINUX_H_
+
+#include "base/basictypes.h"
+
+#include <sys/time.h>
+
+const uint64 MICROS_IN_SECOND = 1000000L;
+
+// A handy class for reliably measuring wall-clock time with decent resolution.
+//
+// We want to measure time with high resolution on Linux. What to do?
+//
+// RDTSC? Sure, but how do you convert it to wall clock time?
+// clock_gettime? It's not in all Linuxes.
+//
+// Let's just use gettimeofday; it's good to the microsecond.
+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.
+  uint64 GetElapsedTicks() const;
+
+  // Returns the elapsed time in milliseconds, rounded to the nearest
+  // millisecond.
+  uint64 GetElapsedMs() const;
+
+  // Returns the elapsed time in seconds, rounded to the nearest second.
+  uint64 GetElapsedSec() const;
+
+  uint64 start_ticks() const { return start_ticks_; }
+
+  // Returns timer frequency from cache, should be less overhead than
+  // ::QueryPerformanceFrequency.
+  static uint64 GetTimerFrequency();
+  // Returns current ticks.
+  static uint64 GetCurrentTicks();
+
+ private:
+  // Captured start time.
+  uint64 start_ticks_;
+};
+
+inline HighresTimer::HighresTimer() {
+  Start();
+}
+
+inline void HighresTimer::Start() {
+  start_ticks_ = GetCurrentTicks();
+}
+
+inline uint64 HighresTimer::GetTimerFrequency() {
+  // Fixed; one "tick" is one microsecond.
+  return MICROS_IN_SECOND;
+}
+
+inline uint64 HighresTimer::GetCurrentTicks() {
+  timeval tv;
+  gettimeofday(&tv, 0);
+
+  return tv.tv_sec * MICROS_IN_SECOND + tv.tv_usec;
+}
+
+inline uint64 HighresTimer::GetElapsedTicks() const {
+  return start_ticks_ - GetCurrentTicks();
+}
+
+#endif  // CHROME_BROWSER_SYNC_UTIL_HIGHRES_TIMER_LINUX_H_