RFR: 8253262: Allocate in DumpRegion is not thread safe

[David Holmes]

On Mon, 21 Sep 2020 16:22:40 GMT, Yumin Qi <minqi at openjdk.org> wrote:

>> It seems to me that the need for locking should be an internal implementation detail of
>> MetaspaceShared::symbol_space_alloc, rather than Symbol operator new.
>
>> It seems to me that the need for locking should be an internal implementation detail of
>> MetaspaceShared::symbol_space_alloc, rather than Symbol operator new.
> 
> I pushed before saw your above comment. The reason for current place is because the following code:
> https://github.com/openjdk/jdk/blob/master/src/hotspot/share/oops/symbol.cpp#L75
>    DEBUG_ONLY(static void* last = 0);
>    void* p = (void*)MetaspaceShared::symbol_space_alloc(size(len)*wordSize);
>    assert(p > last, "must increase monotonically");
>    DEBUG_ONLY(last = p);
>    return p;
> this 'last' is not thread safe either.

My comment was made after the integration so no issue there.

But I think the monotonicity check also belongs inside MetaspaceShared::symbol_space_alloc

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PR: https://git.openjdk.java.net/jdk/pull/216