RFR: 8261127: Cleanup THREAD/TRAPS/CHECK usage in CDS code

[Coleen Phillimore]

On Thu, 4 Feb 2021 13:35:11 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> While examining changes related to the TRAPS macro I noticed that a number of CDS related methods were passed a thread parameter that ended up never being used. Fixing this percolates up the call chain resulting in the ability to remove the parameter from other calls. In some places the thread is needed and has to be manifested via Thread::current(), but these are few and non-critical, and the cleanup of the API (including the benefit to the TRAPS work - see JDK-8252685) makes this worthwhile.
>> 
>> I also changed `Thread* THREAD` to TRAPS where it relates to exception processing (even if CDS diverts to an abort path).
>> 
>> Some uses of CHECK were removed that were only passing THREAD and the called code never triggers any exceptions.
>> 
>> Added commentary where it is not clear why we don't use CHECK.
>> 
>> Testing: local build and CI tiers 1-3
>> 
>> Thanks,
>> David
>
> src/hotspot/share/memory/heapShared.cpp line 690:
> 
>> 688:   resolve_classes_for_subgraphs(fmg_open_archive_subgraph_entry_fields,
>> 689:                                 num_fmg_open_archive_subgraph_entry_fields,
>> 690:                                 THREAD /* exceptions are ignored */);
> 
> Are exceptions ignored or unexpected? This pattern doesn't exist anywhere else as far as I know, otherwise maybe we should have a CLEAR macro in addition to CHECK/CATCH that clears pending exceptions? I don't really like that there may be exceptions lurking through multiple calls.

Ok, so I'm reading this in context. This still looks unusual and possibly problematic without deeper inspection.  It seems like removing TRAPS here also and the callees, and adding this before the functions that clear pending exceptions would be better.
JavaThread* THREAD = JavaThread::current();

> src/hotspot/share/memory/heapShared.cpp line 1275:
> 
>> 1273:   init_subgraph_entry_fields(closed_archive_subgraph_entry_fields,
>> 1274:                              num_closed_archive_subgraph_entry_fields,
>> 1275:                              THREAD /* aborts on exception */);
> 
> So these should really be debug version of CATCH then.

This code makes me wonder if Thread* THREAD doesn't make the intent of this code clearer.

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PR: https://git.openjdk.java.net/jdk/pull/2397