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

[Vladimir Kozlov]

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
>