RFR(trivial): 8232768: Configuration with --disable-cds --enable-generate-classlist should be reported as an error

[Jie Fu]

Hi Magnus,

Thanks for your review and valuable comments.
It is the second case since the VM will report an error for 
DumpLoadedClassList when CDS is disabled.
So generate-classlist *never* will work with CDS disabled.

Updated: http://cr.openjdk.java.net/~jiefu/8232768/webrev.01/

Please review it and give me some advice.

Thanks a lot.
Best regards,
Jie

On 2019/10/22 下午5:54, Magnus Ihse Bursie wrote:
> On 2019-10-22 09:44, Jie Fu wrote:
>> Hi all,
>>
>> May I get reviews for this one-line change?
>>
>> JBS:    https://bugs.openjdk.java.net/browse/JDK-8232768
>> Webrev: http://cr.openjdk.java.net/~jiefu/8232768/webrev.00/
>>
>> This kind of configuration, with both --disable-cds and 
>> --enable-generate-classlist, will fail.
>> The failure is caused by -XX:DumpLoadedClassList [1], which doesn't 
>> work as expected when cds is disabled.
>>
>> It might be better to produce an error.
> I'm not sure I agree with this fix. Checking the code, we make an 
> effort to determine if we should warn the user:
>
>   # Check if it's likely that it's possible to generate the classlist. 
> Depending
>   # on exact jvm configuration it could be possible anyway.
>   if test "x$ENABLE_CDS" = "xtrue" && 
> (HOTSPOT_CHECK_JVM_VARIANT(server) || 
> HOTSPOT_CHECK_JVM_VARIANT(client) || HOTSPOT_CHECK_JVM_FEATURE(cds)); 
> then
>
> Only if the user *explicitly* sets --enable-generate-classlist, the 
> warning is printed. The comment clearly states that this might be 
> possible anyway, given the circumstances, so I believe a warning, and 
> not an error, is the right thing here. The user explicitly requests 
> generate-classlist. We warn that it might not work, but we allow it 
> since it can work in cases we don't really know about.
>
> If it is the case that generate-classlist *never* will work with CDS 
> disabled (this sounds reasonable, but I don't know if this really is 
> the case), and you want to catch this, then I suggest you restructure 
> the code so you catch the CDS && generate-classlist case separately, 
> and give a fatal error for that, and then keep the current check for 
> jvm variants/features and let it keep producing a warning for that.
>
> /Magnus
>>
>> Thanks a lot.
>> Best regards,
>> Jie
>>
>> [1] 
>> http://hg.openjdk.java.net/jdk/jdk/file/ca620b06b5c9/make/GenerateLinkOptData.gmk#l68
>>
>>
>