RFR(S): 8131129: Attempt to define a duplicate BMH$Species class

[Peter Levart]

On 11/05/2015 12:09 AM, Claes Redestad wrote:
> On 2015-11-04 23:31, Peter Levart wrote:
>> Hi Claes,
>>
>> On 11/04/2015 09:12 PM, Claes Redestad wrote:
>>> Hi,
>>>
>>> On 2015-11-04 13:18, Peter Levart wrote:
>>>> Here's what I am thinking, in code:
>>>>
>>>> http://cr.openjdk.java.net/~plevart/jdk9-dev/BMH.race/webrev.02/
>>>>
>>>> Now that definition of BMH subclass is atomic, caching of 
>>>> SpeciesData can be simplified. We don't need special placeholder 
>>>> instances as locks and synchronized static methods. To make BMH 
>>>> subclass definition atomic, we can leverage CHM.computeIfAbsent 
>>>> that does the similar "placeholder" dance, but in much more 
>>>> sophisticated way. BMH logic is much more straightforward and 
>>>> easier to grasp that way.
>>>>
>>>> So what do you think of this version. Your version is logically 
>>>> correct too, so you decide which one is better.
>>>
>>> I gave both patches here a spin and noticed that Peter's variant 
>>> pulls in some 6 extra classes on a jigsaw Hello World test I'm 
>>> playing with (such as ConcurrentHashMap$BaseIterator). Not a strong 
>>> argument in itself, but if there's no stronger reason for your 
>>> version than to clean this up a bit I'd vote in favor of Michael's 
>>> approach...
>>
>> The extra classes needed are not a consequence of using 
>> ConcurrentHashMap per se (as it is already used in CacheLoader to 
>> hold locks), but the result of iteration that is performed here:
>>
>>  431             for (SpeciesData d : CACHE.values()) {
>>  432                 d.initForBootstrap();
>>  433             }
>>
>>
>> ...if this iteration is replaced by iteration over staticSpeciesData 
>> array, there should not be any additional class loaded...
>>
>> I just don't know why this is needed:
>>
>>  367         static { CACHE.put("", EMPTY); }  // make bootstrap 
>> predictable
>>
>> If this is there to force HashMap (or ConcurrentHashMap) to 
>> initialize it's internal table (which it does lazily) and the entry 
>> is otherwise not used, then iterating over staticSpeciesData array 
>> becomes equivalent to iterating over ConcurrentHashMap's values... If 
>> this EMPTY value is used, it can be EMPTY.initForBootstrap()ed 
>> explicitly out of loop.
>
> I'd be happy with getting rid of both loops and the staticSpeciesData 
> array. Refactor the second two rows into a private static method or 
> not and merge with the static block at line 367:
>
> private static void initSpeciesData(SpeciesData speciesData) {
>     CACHE.put(speciesData.typeChars, speciesData);
>     speciesData.initForBootstrap();
> }
>
> static {
>     // Pre-fill the BMH species-data cache with BMH's inner 
> subclasses. All of these classes' SPECIES_DATA
>     // fields must be added to ensure proper cache population.
>     initSpeciesData(EMPTY);
>     initSpeciesData(Species_L.SPECIES_DATA);
>
>     assert speciesDataCachePopulated();
> ...
>
> The assert should take care of failing (a lot of) tests if someone 
> forgets to statically add initSpeciesData for any future (static) 
> inner subclasses of BMH, so I can't think of a real reason to not 
> simplify like this.

Ok, here it is:

http://cr.openjdk.java.net/~plevart/jdk9-dev/BMH.race/webrev.03/

I just moved CACHE registration into SpeciesData.initForBootstrap() 
method, so no new method is needed. Note that patched source now 
contains the same number of lines as original. How does the jigsaw 
HelloWorld score now?

Regards, Peter

>
> /Claes
>
>>
>> Regards, Peter
>>
>>>
>>>> Regards, Peter
>>>>
>>>> On 10/29/2015 04:20 PM, Michael Haupt wrote:
>>>>> Hi Vladimir, Peter,
>>>>>
>>>>> once more, thanks for all your comments. The revised webrev is at 
>>>>> http://cr.openjdk.java.net/~mhaupt/8131129/webrev.01/.
>>>
>>>  however, the access to FAILED_SPECIES_CACHE doesn't seem to be 
>>> thread-safe and needs to be synchronized with a static lock object 
>>> in BoundMethodHandle (initiating different SpeciesData concurrently 
>>> might lead to ConcurrentModificationException when accessing or 
>>> putting values into FAILED_SPECIES_CACHE.
>>>
>>> I'd suggest cleaning up the synchronized methods to lock on specific 
>>> objects while we're at it, and maybe should initialize 
>>> FAILED_SPECIES_CACHE as Collections.emptyList(), since it'll 
>>> typically never be used anyhow:
>>>
>>> http://cr.openjdk.java.net/~redestad/scratch/bmh.race.01/
>>>
>>> Perhaps this clunky implementation is an argument in favor of 
>>> Peter's approach, but it keeps class count in check.
>>>
>>> Thanks!
>>>
>>> /Claes
>>>
>>>>>
>>>>> Best,
>>>>>
>>>>> Michael 
>>>
>>
>