RFR: 8316661: CompilerThread leaks CodeBlob memory when dynamically stopping compiler thread in non-product

[Thomas Schatzl]

On Thu, 21 Sep 2023 19:37:58 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Hi all,
>> 
>>   please review this change to fix a memory leak I found when having `CodeCache::free` call the destructor of `CodeBlob`: when adding the latter, one gets assertion failures that the native memory that `_asm_remarks` and `_dbg_strings` members were not deallocated properly when
>> * stopping a compiler thread due to dynamic compiler thread policy
>> * shutting down the compiler runtime
>> 
>> Testing: gha
>> 
>> Thanks,
>>   Thomas
>
> src/hotspot/share/code/codeCache.cpp line 609:
> 
>> 607:   cb->~CodeBlob();
>> 608:   // Get heap for given CodeBlob and deallocate
>> 609:   get_code_heap(cb)->deallocate(cb);
> 
> I am not sure it look correct - `cb` is used after you call destructor.
> I think it works because destructor only has assert but I don't think it is right thing to do here.

`get_code_heap` and `deallocate` only use the address as a chunk of memory, but not as a `CodeBlob`.
Maybe the parameter to `get_code_heap` should be made `void*` too to make it clear that what's passed here is an opaque address?
`deallocate` unwraps the given pointer to a `HeapBlock` immediately (and gets `cb` as a `void*`), not treating it as a `CodeBlob` any more.
So I think it is the appropriate location to call the destructor.

These two lines resemble a `delete` call: first call the destructor, then pass the pointer to `free`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15858#discussion_r1333528215