Perform CPU sampling by CPU sampling thread only iff processing thread is not running.

Perform CPU sampling by CPU sampling thread only iff processing thread is not running.

- perform CPU profiler sampling in the sampler thread as we used to;
- skip sampling in the sampling thread if processing thread is running;
- only install SIGPROF handler when CPU profiling is enabled.

BUG=v8:2364
Committed: https://code.google.com/p/v8/source/detail?r=12985

[caseq1, 2012-10-19 11:50:03]

Jakob,

contrary to what we discussed, I reinstated sampling from the sampling thread as
we used to do. The reason for that is that currently we never Sleep() on the
processing thread, so I was somewhat frightened this may have side effects on
some usages of --prof (e.g. single core systems).
If nothing else, preserving old implementation of --prof  might be useful for
some time to check the skew (or improvements) of the new implementation.
I'm uploading diff on top of reverted r12745 to minimize the diff, but I think
we should squash revert of r12745 and this one together when landing.

[Jakob Kummerow, 2012-10-19 15:56:41]

Looks good; I have some minor comments.

https://codereview.chromium.org/11231002/diff/1/src/platform-cygwin.cc
File src/platform-cygwin.cc (right):

https://codereview.chromium.org/11231002/diff/1/src/platform-cygwin.cc#newcod...
src/platform-cygwin.cc:789: 
I think the implementation of StartSampling() and StopSampling() is missing
here.

https://codereview.chromium.org/11231002/diff/1/src/platform.h
File src/platform.h (right):

https://codereview.chromium.org/11231002/diff/1/src/platform.h#newcode763
src/platform.h:763: // Perform platform-specific initialization before
DoSample() may be involed.
typo: invoked

https://codereview.chromium.org/11231002/diff/1/src/platform.h#newcode769
src/platform.h:769: StartSampling();
nit: {} please

https://codereview.chromium.org/11231002/diff/1/src/platform.h#newcode773
src/platform.h:773: StopSampling();
nit: {} please

[caseq1, 2012-10-19 16:31:38]

On 2012/10/19 15:56:41, Jakob wrote:
> 
>
https://codereview.chromium.org/11231002/diff/1/src/platform-cygwin.cc#newcod...
> src/platform-cygwin.cc:789: 
> I think the implementation of StartSampling() and StopSampling() is missing
> here.

Ouch! Thanks a lot. Fixed this and everything below.

[Jakob Kummerow, 2012-10-23 12:17:06]

LGTM.

As discussed offline, I'll land this after the branch point.

[caseq1, 2012-11-16 10:22:22]

Fixed crash in tests due to removed check for sampler_