RFR: 8149085: IntegrationTest1.java fails intermittently due to use of semi-initialized TLAB

[Erik Helin]

On 2016-05-24, Stefan Johansson wrote:
> Hi,
> 
> Please review this fix for:
> https://bugs.openjdk.java.net/browse/JDK-8149085
> 
> Webrev:
> http://cr.openjdk.java.net/~sjohanss/8149085/hotspot.00/

Looks reasonable, it is better than the current check. Reviewed.

Thanks,
Erik

> Summary:
> Thread::cooked_allocated_bytes() tries to give a good estimation of how much
> has been allocated by a given thread. It does this by adding the stored
> _allocated_bytes valued, incremented when a TLAB is retired, with the used
> bytes from the currently active TLAB. This works fine when
> cooked_allocated_bytes() is called by the current thread, but when called to
> query a different thread there is a risk that the thread is in the middle of
> retiring its TLAB. In such case there was risk that a bad used_bytes() value
> was used and in turn caused the test in question to fail.
> 
> A similar issue seems to have been semi-fixed before, the removed code
> suggests that making sure that the signed used bytes size is more than zero
> is enough to make it a valid TLAB, but it turns out this is not enough.
> Instead making sure that the used bytes value is less than the max allowed
> TLAB-size should ensure that the TLAB has been fully initialized.
> 
> As the added comment suggests there is still a race present in this code,
> and I don't intend to fix this now because I see this more as a fast
> sampling function than something that we should rely on.
> 
> Testing:
> Verified fix locally. RBT run for G1 and Parallel is ongoing.
> 
> Thanks,
> Stefan
>