Fix issue 410: test-log/ProfLazyMode flakinness under Linux.

Fix issue 410: test-log/ProfLazyMode flakinness under Linux.

I found two causes of flakinness:
 - SIGPROF signal isn't delivered to a process;
 - Profiler thread (the one that retrieves tick events from
   the queue and writes to log) doesn't get a CPU;
Both are fixed.

The script from bug description with run count increased to 200 runs without any test failures.

OS X and Windows are unaffected because they don't use signals mechanism.

BUG=http://code.google.com/p/v8/issues/detail?id=410
TEST=see bug description

Committed: http://code.google.com/p/v8/source/detail?r=2547

[Søren Thygesen Gjesse, 2009-07-28 08:12:37]

LGTM

Would it be an idea to use a high priority thread on Linux as well or does the
SIGPROF have advantages over it?

http://codereview.chromium.org/159406/diff/4/1002
File test/cctest/test-log.cc (right):

http://codereview.chromium.org/159406/diff/4/1002#newcode150
Line 150: static bool was_sigprof_received = true;
Maybe move this down to 'struct sigaction old_sigprof_handler;'

[Mikhail Naganov, 2009-07-28 08:34:15]

Yes, I'm thinking about switching from SIGPROF to a hi-prio thread too. Not only
this is more reliable, but it provides a much better resolution. E.g. running V8
benchmarks on Mac gives 9500 samples from 9.968 s (almost every ms!), while on
Linux it gives only 1000 samples from the same 10 seconds---about 10 times
worse!

The only problem is that Linux PThreads doesn't have pthread_suspend implemented
(on Mac we work with threads using Mach primitives directly), so I will need to
introduce some workaround.

http://codereview.chromium.org/159406/diff/4/1002
File test/cctest/test-log.cc (right):

http://codereview.chromium.org/159406/diff/4/1002#newcode150
Line 150: static bool was_sigprof_received = true;
On 2009/07/28 08:12:37, Søren Gjesse wrote:
> Maybe move this down to 'struct sigaction old_sigprof_handler;'

This will add another 'ifdef' branch around lines 226-227. I think having
was_sigprof_received always declared is more straightforward.