RFR: 8255070: Shenandoah: use single thread for concurrent CLD liveness test

[Azeem Jiva]

On Tue, 20 Oct 2020 23:48:58 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> Since the concurrent liveness test does not touch any oops, there is no point to use multi-thread for the task, they
> just duplicate the work.
> Also, multi-thread version requires to acquire ClassLoaderGraph_lock early, which is deadlock prone.

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 1944:

> 1942:
> 1943:   // Roots related to concurrent class unloading
> 1944:   ShenandoahClassLoaderDataRoots<true /* concurrent */, true /* single thread*/>

Should the first input be false?

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PR: https://git.openjdk.java.net/jdk/pull/777