RFR: 8252921: NMT overwrite memory type for region assert when building dynamic archive

[Zhengyu Gu]

On Wed, 16 Sep 2020 02:49:45 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Thread stack is currently unregistered with NMT in Thread's destructor. Apparently, only Java thread invokes destructor
>> before thread exits.  For NonJavaThread, e.g. ConcurrentGCThread, thread may exit while its "Thread" object continues
>> alive, therefore, its thread stack is still "alive" from NMT perspective. Once thread exits, the virtual memory for the
>> thread stack can be reserved again, that confused NMT.  The solution is to move thread stack unregistration code to
>> post_run() method.
>
> src/hotspot/share/runtime/thread.hpp line 762:
> 
>> 760:  public:
>> 761:   // Stack overflow support
>> 762:   address stack_base() const           { return _stack_base; }
> 
> Why did you remove the assertion? We want the assertion in general to ensure there are no improper uses of stack_base().

We now reset NonJavaThread's stack base and size,  so _stack_base == NULL is possible, e.g. when generating hs_err
report, as we should now see empty stack for "G1 Main Marker" thread in original bug report.

You do have a valid point for the assertion. I think following assertion is more precise:

assert(_stack_base != NULL || Thread::current() != NULL, "Sanity check");

What you think?

Thanks

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PR: https://git.openjdk.java.net/jdk/pull/185