RFR: 8252049: Native memory leak in ciMethodData ctor [v4]

[Kim Barrett]

On Mon, 7 Dec 2020 15:38:28 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> `ciMethodData` embeds `MethodData` to snapshot a state from the original `MethodData` instance.
>> But `MethodData` embeds a `Mutex` which allocates a platform-specific implementation on C-heap.
>> The `Mutex` is overwritten with `0`s, but the resources aren't deallocated, so the leak occurs.
>> 
>> Proposed fix is to run Mutex destructor right away. 
>> 
>> Initially, I thought about switching to `Mutex*`, but then I found that Coleen already tried that and observed a performance regression [1]. So, for now I chose the conservative approach.
>> 
>> In the longer term, I would consider replacing `MethodData::_extra_data_lock` with a lock-free scheme. Having a lock-per-MDO looks kind of excessive.
>> 
>> Testing:
>> - [x] verified that no memory leak observed with the reported test
>> - [x] tier1-4
>> 
>> [1] https://mail.openjdk.java.net/pipermail/hotspot-dev/2019-October/039783.html
>
> Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanups

One lingering question.  The name CompilerCounters seems much better, BTW.

src/hotspot/share/oops/methodData.hpp line 1987:

> 1985: 
> 1986:   public:
> 1987:     CompilerCounters() : _nof_decompiles(0), _nof_overflow_recompiles(0), _nof_overflow_traps(0) {

This doesn't initialize _creation_mileage.  Is that a bug?  Should that be a constructor argument?

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PR: https://git.openjdk.java.net/jdk/pull/1478