Implemented ScopedFakeTime, faking rtc::TimeNanos.

Implemented ScopedFakeTime, faking rtc::TimeNanos.

BUG=5940

[nisse-webrtc, 2016-05-27 12:40:24]

nisse@webrtc.org changed reviewers:
+ pbos@webrtc.org, sprang@webrtc.org

[nisse-webrtc, 2016-05-27 12:40:25]

Here's a first implementation of a ScopedFakeTime.

[pbos-webrtc, 2016-05-31 22:34:16]

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc
File webrtc/base/timeutils.cc (right):

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc#...
webrtc/base/timeutils.cc:36: FakeTimeInterface* global_fake_time = nullptr;
g_fake_time

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc#...
webrtc/base/timeutils.cc:41: RTC_CHECK(!global_fake_time || !fake_time);
if (!fake_time)
  RTC_CHECK(!global_fake_time);

Reads easier to me.

[pbos-webrtc, 2016-05-31 22:35:35]

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:40: ScopedFakeTime() : ScopedFakeTime(rtc::TimeNanos())
{}
Is this one useful or added prematurely?

[nisse-webrtc, 2016-06-01 07:35:36]

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:40: ScopedFakeTime() : ScopedFakeTime(rtc::TimeNanos())
{}
On 2016/05/31 22:35:35, pbos-webrtc wrote:
> Is this one useful or added prematurely?

It's all a bit premature, the unittest uses both constructors. Not clear which
variant is most useful. And I'm fine with keeping this on hold until we've
identified one test to use it. It's not clear to me if it's needed for testing
cl https://codereview.webrtc.org/2017443003/ or not.

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc
File webrtc/base/timeutils.cc (right):

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc#...
webrtc/base/timeutils.cc:36: FakeTimeInterface* global_fake_time = nullptr;
On 2016/05/31 22:34:16, pbos-webrtc wrote:
> g_fake_time

Done.

https://codereview.webrtc.org/2016863003/diff/40001/webrtc/base/timeutils.cc#...
webrtc/base/timeutils.cc:41: RTC_CHECK(!global_fake_time || !fake_time);
On 2016/05/31 22:34:16, pbos-webrtc wrote:
> if (!fake_time)
>   RTC_CHECK(!global_fake_time);
> 
> Reads easier to me.

Changed to

  if (fake_time)
    RTC_CHECK(!g_fake_time);

[pthatcher1, 2016-06-03 00:34:44]

pthatcher@webrtc.org changed reviewers:
+ deadbeef@webrtc.org, pthatcher@webrtc.org

[pthatcher1, 2016-06-03 00:34:45]

Adding Taylor, who recently wrote FakeClock which looks very similar. 

In short, I don't think we need this CL because it's already there, or will be
soon.

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:35: class ScopedFakeTime : public FakeTime {
Have you seen FakeClock in fakeclock.h? It looks *very* similar.

And ScopedFakeClock is being added to it in an upcoming CL.

[nisse-webrtc, 2016-06-03 11:40:07]

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:35: class ScopedFakeTime : public FakeTime {
On 2016/06/03 00:34:45, pthatcher1 wrote:
> Have you seen FakeClock in fakeclock.h? It looks *very* similar.
> 
> And ScopedFakeClock is being added to it in an upcoming CL.

It look very similar indeed. Great minds think alike ;-)

I'm happy to leave this to you. Taylor, have a look the ScopedFakeTime in this
cl, maybe there's something there which is useful to you, or maybe there isn't.

[nisse-webrtc, 2016-06-03 11:40:07]

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:35: class ScopedFakeTime : public FakeTime {
On 2016/06/03 00:34:45, pthatcher1 wrote:
> Have you seen FakeClock in fakeclock.h? It looks *very* similar.
> 
> And ScopedFakeClock is being added to it in an upcoming CL.

It look very similar indeed. Great minds think alike ;-)

I'm happy to leave this to you. Taylor, have a look the ScopedFakeTime in this
cl, maybe there's something there which is useful to you, or maybe there isn't.

[Taylor Brandstetter, 2016-06-03 16:30:16]

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h
File webrtc/base/faketime.h (right):

https://codereview.webrtc.org/2016863003/diff/60001/webrtc/base/faketime.h#ne...
webrtc/base/faketime.h:35: class ScopedFakeTime : public FakeTime {
On 2016/06/03 11:40:07, nisse-webrtc wrote:
> On 2016/06/03 00:34:45, pthatcher1 wrote:
> > Have you seen FakeClock in fakeclock.h? It looks *very* similar.
> > 
> > And ScopedFakeClock is being added to it in an upcoming CL.
> 
> It look very similar indeed. Great minds think alike ;-)
> 
> I'm happy to leave this to you. Taylor, have a look the ScopedFakeTime in this
> cl, maybe there's something there which is useful to you, or maybe there
isn't.

Aside from FakeTime taking a time in its constructor, and naming, I think our
implementations are exactly the same. I'm honestly amazed.

By the way, take a look at this upcoming CL:
https://codereview.webrtc.org/2024813004/

The goal is to handle events that piggyback off of each other. If the expiration
of one timeout triggers another timeout, then it's not enough to advance the
clock once, because that will only trigger the first timeout. So the
SIMULATED_WAIT macro advances the fake clock by 1ms ticks, processing all
pending events on each tick. Let me know what you think.