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

[Stefan Johansson]

Hi,

Please review this fix for:
https://bugs.openjdk.java.net/browse/JDK-8149085

Webrev:
http://cr.openjdk.java.net/~sjohanss/8149085/hotspot.00/

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