RFR: 8255883: Avoid multiple GeneratedMethodAccessor for same NativeMethod… [v5]

[Alan Bateman]

On Thu, 12 Nov 2020 04:23:37 GMT, Hui Shi <hshi at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/reflect/NativeConstructorAccessorImpl.java line 44:
>> 
>>> 42:     private DelegatingConstructorAccessorImpl parent;
>>> 43:     private int numInvocations;
>>> 44:     private int generated;
>> 
>> What is the reason for using an int? I remember there was a suggestion for three states but two states seems okay so curious why it was changed from boolean to int.
>> The restoring to 0 in the event of failure should probably be a volatile-write. Might be clearer to declare it as a volatile.
>
> @AlanBateman 
> 
>> What is the reason for using an int? I remember there was a suggestion for three states but two states seems okay so curious why it was changed from boolean to int.
> 
> shipilev suggested not to use sub-word CAS, so change compareAndSetBoolean to compareAndSetInt. Change field "generated" from boolean to int doesn't increase object size (no extra byte/boolean to fold into same word).
> 
>> The restoring to 0 in the event of failure should probably be a volatile-write. Might be clearer to declare it as a volatile.
> 
> "generated" field  is read once and CAS once in this method. It doesn't likely cached and no visibiliy order required.

okay, although I think it would be clearer for maintainers to declare it as volatile because it is set with CAS.

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PR: https://git.openjdk.java.net/jdk/pull/1070