[11] RFR(S): 8209670: CompilerThread releases code buffer in destructor is unsafe

[Tobias Hartmann]

Thanks Vladimir! Could I please get another review for this?

Best regards,
Tobias

On 20.08.2018 19:57, Vladimir Kozlov wrote:
> Looks good to me.
> 
> Thanks,
> Vladimir
> 
> On 8/20/18 4:06 AM, Tobias Hartmann wrote:
>> Hi,
>>
>> please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8209670
>>
>> Since JDK-8198756 [1], compiler threads can be added and removed at runtime. C1 compiler threads use
>> a temporary code buffer that is allocated once the thread is created and needs to be freed if the
>> thread is removed to avoid a memory leak (see JDK-8205499 [2]). Freeing is currently done in the
>> thread destructor after the thread was removed from the thread list. This means that although we are
>> holding the CodeCache_lock, freeing of the code blob might interfere with non-locking safepoint code
>> that is concurrently walking the code cache.
>>
>> The fix is to free the temporary buffers at the two places where compiler threads are removed:
>> http://cr.openjdk.java.net/~thartmann/8209670/webrev.00/
>>
>> This should be safe because it partially restores the code to pre-JDK-8205499. Testing on
>> hs-tier1-3, jdk-tier1-3 and hs-precheckin-comp passed.
>>
>> An alternative would be to disable UseDynamicNumberOfCompilerThreads and do a proper fix in JDK 12:
>> http://cr.openjdk.java.net/~thartmann/8209670/webrev.01/
>>
>> Thanks,
>> Tobias
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8198756
>> [2] https://bugs.openjdk.java.net/browse/JDK-8205499
>>