Support higher CPU profiler sampling rate on Mac OS X

Support higher CPU profiler sampling rate on Mac OS X

This change moves sampling to the profiler events processing thread and allows to configure sampling interval on Mac OS X.

SamplerThread::SampleContext method was changed into Sampler::DoSample.

BUG=v8:2814

[yurys, 2013-08-21 08:40:24]

ping

[yurys, 2013-08-23 06:14:51]

Guys, any objections to this change?

[Benedikt Meurer, 2013-08-23 06:40:27]

On 2013/08/23 06:14:51, Yury Semikhatsky wrote:
> Guys, any objections to this change?

Maybe I'm missing something, but what is the objective here? You're switching
the CPU profiler on Mac OS X to use POSIX signals, so most of the Mac OS X
specific code you move around here is going away, right?

[yurys, 2013-08-23 07:23:55]

On 2013/08/23 06:40:27, Benedikt Meurer wrote:
> On 2013/08/23 06:14:51, Yury Semikhatsky wrote:
> > Guys, any objections to this change?
> 
> Maybe I'm missing something, but what is the objective here? You're switching
> the CPU profiler on Mac OS X to use POSIX signals, so most of the Mac OS X
> specific code you move around here is going away, right?

Correct. But the full picture is the following. A few days ago I realized that
we could use signals on Mac OS X and came up with the patch changing Mac OS X
implementation to use signals. That patch is based on the pile of 4 other
changes (including this one which had been sent for review 4 days before the CL
about signals) to the CPU profiler that stuck due to V8 tree being closed for 2
weeks. If possible I'd prefer to just land all that CLs consecutively instead of
taking out one of them from the middle of the queue and rebasing all the
following ones trying to merge parts of this change into one of them.

[Benedikt Meurer, 2013-08-23 07:30:06]

On 2013/08/23 07:23:55, Yury Semikhatsky wrote:
> On 2013/08/23 06:40:27, Benedikt Meurer wrote:
> > On 2013/08/23 06:14:51, Yury Semikhatsky wrote:
> > > Guys, any objections to this change?
> > 
> > Maybe I'm missing something, but what is the objective here? You're
switching
> > the CPU profiler on Mac OS X to use POSIX signals, so most of the Mac OS X
> > specific code you move around here is going away, right?
> 
> Correct. But the full picture is the following. A few days ago I realized that
> we could use signals on Mac OS X and came up with the patch changing Mac OS X
> implementation to use signals. That patch is based on the pile of 4 other
> changes (including this one which had been sent for review 4 days before the
CL
> about signals) to the CPU profiler that stuck due to V8 tree being closed for
2
> weeks. If possible I'd prefer to just land all that CLs consecutively instead
of
> taking out one of them from the middle of the queue and rebasing all the
> following ones trying to merge parts of this change into one of them.

Yeah, sorry, we're not happy with that either.