RFR: 8080106: Refactor setup of parallel GC threads

[Stefan Karlsson]

Hi Jon,

On 2015-05-14 22:48, Jon Masamitsu wrote:
> Stefan,
>
> I'll send mail for each of the CR's (so hold applause :-) until you
> see the last one).
>
>
> On 05/13/2015 06:17 AM, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review these patches to unify the ways we specify the number 
>> of used worker threads. The main goal for these patches is to get rid 
>> of CollectedHeap::set_par_threads() and CollectedHeap::n_par_threads().
>>
>> The RFE has been split into multiple sub-tasks:
>>  8080109: Use single-threaded code in 
>> Threads::possibly_parallel_oops_do when running with only one worker 
>> thread
>>  8080110: Remove usage of CollectedHeap::n_par_threads() from root 
>> processing
>>  8080111: Remove SubTaskDone::_n_threads
>>  8080112: Replace and remove the last usages of 
>> CollectedHeap::n_par_threads()
>>  8080113: Remove CollectedHeap::set_par_threads()
>>
>> See the description below for each individual patch:
>>
>> ---
>> http://cr.openjdk.java.net/~stefank/8080109/webrev.00
>> 8080109: Use single-threaded code in 
>> Threads::possibly_parallel_oops_do when running with only one worker 
>> thread
>>
>> Today, the root processing code differentiates between two types of 
>> single-threaded executions:
>>
>> 1) n_par_threads() == 0, used from Serial GC and other code paths 
>> that executes the root processing from the VM Thread.
>> 2) n_par_threads() == 1, used from non-Serial GCs when the 
>> root_processing is executed by one GC worker thread.
>>
>> Today, the only code difference is that the latter will use cmpxchg 
>> to claim the threads in Threads::possibly_parallel_oops_do.
>>
>> I propose that we use the same code for both values of 
>> n_par_threads(), and only use the cmpxchg version if we are running 
>> with more than one worker thread.
>>
>> ---
> Looks good.  Reviewed.

Thanks,
StefanK

>
> Jon
>