RFR(S) 8210388 Use hash table to store archived subgraph_info records

[Jiangli Zhou]

Hi Ioi,


On 9/20/18 11:28 AM, Ioi Lam wrote:
> http://cr.openjdk.java.net/~iklam/jdk12/8210388-hashtable-subgraph-info.v01/ 
>
> https://bugs.openjdk.java.net/browse/JDK-8210388
>
> Here's another small step towards CDS support for Lambda (JDK-8198698).
>
> Replace the linear search of ArchivedKlassSubGraphInfoRecord with
> a hashtable. Currently we have just 6 such records, but with Lambda 
> support
> that number is going to increase substiantially.
>
>      Shared subgraphs table stats
>      Number of entries       :         6
>      Total bytes used        :        72
>      Average bytes per entry :    12.000
>      Average bucket size     :     6.000
>      Variance of bucket size :     0.000
>      Std. dev. of bucket size:     0.000
>      Empty buckets           :         0
>      Value_Only buckets      :         0
>      Other buckets           :         1
>
> I also took the chance to clean up the use of CompactHashtableWriter in
> the symbol/string tables. In doing so, I fixed a bug where
> SymbolTable::copy_shared_symbol_table was skipping symbols with zero 
> hashcodes.
> This should be done for the string table only.
>
> Jiangli, could you help me with this comments?
>
>     unsigned int hash = java_lang_String::hash_code(s);
>     if (hash == 0) {
>       // We do not archive Strings with a 0 hashcode because ......
>       return true;
>     }
The intent was to prevent possible write into the closed archive region 
when identity_hash was called on an empty String. The empty String is 
archived in the open archive heap region. This may not be necessary as 
we always pre-compute identity hash for archived object. If you want to 
remove this restriction, please be careful to verify all possible cases.

Thanks,
Jiangli
>
>
> Thanks
> - Ioi