CMS parallel initial mark; vm thread sneaking in Thread::try_lock()

Jon Masamitsu jon.masamitsu at
Fri Jun 21 15:50:08 PDT 2013

Yes, remove the assert.


On 6/19/2013 10:39 AM, Hiroshi Yamauchi wrote:
>>> Now, if I comment out the assert, it seems to work (though I haven't
>>> tested it very long.) This may be good if in fact sneak won't happen
>>> with try_lock()/unlock() only.
>>> I haven't tried this, but another potential approach might be to give
>>> up sampling (just return) if it's called by the VM thread at a
>>> safepoint, though the VM thread might allocate a large object, and the
>>> evenness of the sample distribution could suffer to some extent.
>> I'd just remove the assert :)
>> As already mentioned multiple times, try_lock() does never actually
>> block the thread, so the vm thread cannot actually sneak, as you already
>> noticed in your question to David, and he confirmed. The guarded code
>> can also never block, it's just a few assignments.
> Removing the assert sounds good to me.
> Jon, what do you think?

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