Improving the fake clock and using it to fix a flaky STUN timeout test.

webrtc/base/fakeclock.h

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_BASE_FAKECLOCK_H_
 #define WEBRTC_BASE_FAKECLOCK_H_
 
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/timedelta.h"
 #include "webrtc/base/timeutils.h"
 
 namespace rtc {
 
 // Fake clock for use with unit tests, which does not tick on its own.
 // Starts at time 0.
+//
+// TODO(deadbeef): Unify with webrtc::SimulatedClock.
 class FakeClock : public ClockInterface {
  public:
   ~FakeClock() override {}
 
   // ClockInterface implementation.
   uint64_t TimeNanos() const override;
 
   // Methods that can be used by the test to control the time.
 
   // Should only be used to set a time in the future.
   void SetTimeNanos(uint64_t nanos);
 
   void AdvanceTime(TimeDelta delta);
 
  private:
   CriticalSection lock_;
   uint64_t time_ GUARDED_BY(lock_) = 0u;
 };
 
+// Helper class which creates and sets a fake clock as the global clock in
+// its constructor, and unsets and deletes it in its destructor.
+class ScopedFakeClock {

[pthatcher1, 2016/06/01 22:38:14]

Does this work in C++?

class ScopedFakeClock : FakeClock {
 public:
  ScopedFakeClock() { SetClock(this); }
  ~ScopedFakeClock() { SetClock(nullptr); }
}

?

That way, the caller would't have to call "sfc.clock()".  They could just use
the clock.

[Taylor Brandstetter, 2016/06/01 23:28:37]

Done.

+ public:
+  ScopedFakeClock() { SetClock(&clock_); }
+
+  ~ScopedFakeClock() { SetClock(nullptr); }

[pthatcher1, 2016/06/01 22:38:14]

Should we do this?

public:
 ScopedFakeClock() { old_clock_ = g_clock; SetClock(this); }
 ~ScopedFakeClock() { SetClock(old_clock_); }

private:
 old_clock_ = nullptr;



Otherwise, we might blow away a clock that was supposed to be there.  But I
don't know who will set g_clock to anything but nullptr except a unit test.

[Taylor Brandstetter, 2016/06/01 23:28:37]

I hadn't *intended* for there to be multiple fake clocks in use in the same
test. But I guess it's possible, so might as well do this.

+
+  FakeClock& clock() { return clock_; }
+
+ private:
+  FakeClock clock_;
+};
+
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_FAKECLOCK_H_