RFR: 8253262: Allocate in DumpRegion is not thread safe

[Calvin Cheung]

On Thu, 17 Sep 2020 04:52:29 GMT, Yumin Qi <minqi at openjdk.org> wrote:

> At CDS dump, the symbols are allocated from _dump_region (DumpRegion) which is global, and not thread safe when
> executed in JavaThread. Add a lock DumpRegoin_lock to guard symbol allocation from it.
> Tests: tier1-4

Looks good.

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Marked as reviewed by ccheung (Reviewer).

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