RFR 8150607 - Clean up CompactHashtable

[Jiangli Zhou]

Ioi,

> On Apr 11, 2016, at 7:11 PM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> Hi Jiangli,
> 
> 
> Thanks for the review:
> 
> On 4/11/16 6:44 PM, Jiangli Zhou wrote:
>> Hi Ioi,
>> 
>> I like the more structural way of reading/writing the compact table with SimpleCompactHashtable. It looks quite clean overall.
>> 
>> - How about using VALUE_ONLY_BUCKET_TYPE, which is more descriptive than TINY_BUCKET_TYPE?
>> 
> OK, I will make the change.
> 
>> - The following assert in CompactSymbolTableWriter::add() limits the total shared space size to be less than MAX_SHARED_DELTA unnecessarily. Symbols are allocated from the RO space at dump time. We only need to make sure the max delta between the ‘base_address’ and the end of RO space is less than MAX_SHARED_DELTA. This is not a new issue introduced by your change, you don’t have to address that as part of this change if you prefer. I’ll file a separate RFE.
>> 
> I think it's better to do this in a separate RFE since MAX_SHARED_DELTA is used elsewhere as well.

I filed JDK-8154108 <https://bugs.openjdk.java.net/browse/JDK-8154108>.

> 
>>  171 void CompactSymbolTableWriter::add(unsigned int hash, Symbol *symbol) {
>>  172   address base_address = address(MetaspaceShared::shared_rs()->base());
>>  173   uintx max_delta = uintx(MetaspaceShared::shared_rs()->size());
>>  174   assert(max_delta <= MAX_SHARED_DELTA, "range check");
>> 
>> - Why is the default RO space size increased?
>> 
> That's because the symbol table is moved from RW to RO, so I had to change the RO minimum size, or else test/runtime/SharedArchiveFile/LimitSharedSizes.java would fail.

Ok.

Thanks,
Jiangli

>> - src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/memory/SymbolTable.java
>> - src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/utilities/CompactHashTable.java
>>   Copyright year.
> 
> Will fix.
> 
> Thanks
> - Ioi
>> 
>> Thanks,
>> Jiangli
>> 
>>> On Mar 31, 2016, at 10:43 PM, Ioi Lam <ioi.lam at oracle.com <mailto:ioi.lam at oracle.com>> wrote:
>>> 
>>> Please review
>>> 
>>> http://cr.openjdk.java.net/~iklam/jdk9/8150607_cleanup_compact_hashtable.v01/ <http://cr.openjdk.java.net/%7Eiklam/jdk9/8150607_cleanup_compact_hashtable.v01/>
>>> 
>>> Bug: Clean up CompactHashtable
>>> 
>>>    https://bugs.openjdk.java.net/browse/JDK-8150607 <https://bugs.openjdk.java.net/browse/JDK-8150607>
>>> 
>>> Summary of fix:
>>> 
>>> [1] Instead of reading/writing the table bit-by-bit, which is tedious and
>>>    error prone, use SimpleCompactHashtable::serialize(), which is more
>>>    structural.
>>> 
>>> [2] Split up the _buckets and _entries into two separate arrays, so the
>>>    dumping and walking code is easier to understand
>>> 
>>>    (see comments above SimpleCompactHashtable declaration)
>>>    These 2 arrays are now allocated from the RO region (used to be in RW)
>>> 
>>> [3] Renamed a few things
>>> 
>>>    COMPACT_BUCKET_TYPE -> TINY_BUCKET_TYPE
>>>        (having something called "compact" in CompactHashtable is confusing)
>>> 
>>>    The old names "dump_table" (actually dumping the buckets) and
>>>    "dump_buckets" (actually dumping the entries) were conflicting with
>>>    terminology used elsewhere. Now the terminology is unified:
>>>        "buckets" = the main index, "entries" = the second level.
>>> 
>>>    lookup_entry -> decode_entry (it wasn't doing any lookup)
>>> 
>>> [4] Changed all "*p++" to "array->at_put", so out-of-bounds can be
>>>    checked with assert.
>>> 
>>> [5] Replaced all juint to u4 (suggested by Coleen)
>>> 
>>> [6] templatize the iterator (see CompactHashtable::symbols_do ->
>>>    SimpleCompactHashtable::iterate)
>>> 
>>> [7] I also added a test case using Serviceability Agent -- due to the lack of
>>>    a regression test, the walking of the compact hashtable in SA had been
>>>    broken for a while before it was fixed in JDK-8151368, so having a test
>>>    case would make the code more maintainable.
>>> 
>>> Tests:
>>> 
>>>    Hotspot JTREG tests
>>> 
>>> Thanks
>>> - Ioi
>> 
> 

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