RFR: 8364929: Assign unique id to each AdapterBlob stored in AOTCodeCache [v4]

[Ashutosh Mehra]

On Thu, 2 Oct 2025 18:54:57 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Ashutosh Mehra has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Replace overflow check if guarantee statement
>>   
>>   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>
> src/hotspot/share/runtime/sharedRuntime.cpp line 2605:
> 
>> 2603: AdapterHandlerEntry* AdapterHandlerLibrary::new_entry(AdapterFingerPrint* fingerprint) {
>> 2604:   uint id = (uint)AtomicAccess::add((int*)&_id_counter, 1);
>> 2605:   guarantee(id > 0, "id_counter overflow");
> 
> I think we can even change this to an assert. We limit the AOT metaspace size to `UnscaledClassSpaceMax` which is 4GB. 
> 
> https://github.com/openjdk/jdk/blob/1d55adee11fc2fdbf2e009e1308b763fd7217dad/src/hotspot/share/cds/aotMetaspace.cpp#L304C24-L304C45
> 
> All AOT methods would have to live within the AOT metaspace , so we will have much fewer than 2^32 methods, which means will we have much fewer than 2^32 signatures. So the `id` will never overflow. Maybe change this to:
> 
> 
> assert(id > 0, "we can never overflow because AOT cache cannot contain more than 2^32 methods");

Changed it to assert as suggested

> src/hotspot/share/runtime/sharedRuntime.hpp line 687:
> 
>> 685: 
>> 686:  private:
>> 687:   uint _id;
> 
> This can be moved near `_linked` so it can fit in the existing unused padding.

Good point. Done.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27553#discussion_r2399881707
PR Review Comment: https://git.openjdk.org/jdk/pull/27553#discussion_r2399882092