base/time/tick_clock.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_TICK_CLOCK_H_
   6 #define BASE_TICK_CLOCK_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/time/time.h"
  10
  11 namespace base {
  12
  13 // A TickClock is an interface for objects that vend TimeTicks.  It is
  14 // intended to be able to test the behavior of classes with respect to
  15 // non-decreasing time.
  16 //
  17 // See DefaultTickClock (base/time/default_tick_clock.h) for the default
  18 // implementation that simply uses TimeTicks::Now().
  19 //
  20 // (Other implementations that use TimeTicks::NowFromSystemTime() should
  21 // be added as needed.)
  22 //
  23 // See SimpleTestTickClock (base/test/simple_test_tick_clock.h) for a
  24 // simple test implementation.
  25 //
  26 // See Clock (base/time/clock.h) for the equivalent interface for Times.
  27 class BASE_EXPORT TickClock {
  28  public:
  29   virtual ~TickClock();
  30
  31   // NowTicks() must be safe to call from any thread.  The caller may
  32   // assume that NowTicks() is monotonic (but not strictly monotonic).
  33   // In other words, the returned TimeTicks will never decrease with
  34   // time, although they might "stand still".
  35   virtual TimeTicks NowTicks() = 0;
  36 };
  37
  38 }  // namespace base
  39
  40 #endif  // BASE_TICK_CLOCK_H_