RFR: 8215889: assert(!_unloading) failed: This oop is not available to unloading class loader data with ZGC

[Erik Österlund]

Hi Nils,

Thanks for the review.

/Erik

On 2019-01-10 15:28, Nils Eliasson wrote:
> Hi Erik,
>
> Nice work! Looks good.
>
> // Nils
>
> On 2019-01-07 10:51, Erik Österlund wrote:
>> Hi,
>>
>> There are SpeculativeTrapData entries in the extra data space of MDOs 
>> that are currently not being checked for stale Method* entries due to 
>> concurrent class unloading.
>>
>> The fix involves lazily cleaning SpeculativeTrapData entries during 
>> ciMethodData::load_extra_data(), which unpacks the extra data from 
>> the source MDO to the ci copy of the MDO, that the compiler 
>> subsequently uses as reference during the ongoing compilation, and 
>> needs to have live metadata only.
>>
>> A new ciMethodData::prepare_metadata() method is added to ci MDO 
>> mirrors that lazily cleans the extra data space and pre-caches the 
>> ciEnv with all the metadata it encounters. When creating ciMethod 
>> handles, the Compile_lock might be taken, which strictly requires 
>> safepoint checking. Therefore, prepare_metadata() loops until it can 
>> pre-cache all live metadata without any cache misses, because that 
>> implies the subsequent code copying the MDO can not safepoint while 
>> extracting the extra data from the MDO, which is a requirement as 1) 
>> a safepoint may invalidate the metadata again, 2) both the cleaning 
>> (from the concurrent GC thread) and extraction (from the compiler 
>> thread) must be done under the mdo->extra_data_lock().
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8215889
>>
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8215889/webrev.00/
>>
>> Testing: hs-tier1-6, and a bunch of local testing, including 24 hours 
>> kitchensink in fastdebug.
>>
>> Thanks,
>> /Erik