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Comment #5 on issue 2874 by [email protected]: Threading problems in
test-api
http://code.google.com/p/v8/issues/detail?id=2874
After extensive debugging, we just discovered that this bug is caused by
the design of the CPU profiler. We have the following scenario:
1. The JavaScript thread is executing some C++ function, which calls into
one of the Isolate methods that aquire the mutex in Isolate.
2. Then the sampler thread sends a SIGPROF to the JavaScript thread.
3. The JavaScript thread enters the signal handler while the mutex is
locked.
4. The signal handler (in the JavaScript thread) tries to acquire the mutex
again to gain access to the Simulator, which fails (of course).
This bug was there forever, but it probably showed up as seldom mysterious
crasher, which was not reproducible. It is now almost reproducible because
(a) we actually check the result of synchronization primitives and (b) the
profiling interval was reduced to 1ms.
Note that this particular bug affects only the simulators, and we may get
around this by simply disabling profile if USE_SIMULATOR is defined.
But while looking through the code, we discovered that there are other
issues that'll affect production code. For example, we assume that
pthread_getspecific() is async-signal-safe, which seems to hold for the
current implementation in glibc (NTPL), but is by no means guaranteed (not
even talking about Mac OS X, *BSD, Solaris, etc. here).
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