Request for Review (M) - 6858051: Create GC worker threads dynamically

Jon Masamitsu jon.masamitsu at
Thu Apr 28 22:40:57 UTC 2016


In order to reduce the dependency of WorkGang on AdaptiveSizePolicy,
removed AdaptiveSizePolicy::initial_number_of_workers() and duplicated 
the code
in GCTaskManager::initialize() and AbstractWorkGang::initialize_workers().

Moved AdaptiveSizePolicy::add_workers() to WorkerManager::add_workers() in
file shared/workerManager.hpp

Removed guard DisableStartThread from add_workers() and always start the

Removed the bool return value from WorkerManager::add_workers (and let 
that rippled down
to the callers).

Changed WorkerManager::add_workers() to return the number of created workers
(removed inout on parameters) and let the callers of 
adjust their _active_workers to be consistent with the number of created 

Changed number of workers created at initialization from 2 to 1.

Please let me know if I forgot anything.




On 04/26/2016 10:06 PM, Jon Masamitsu wrote:
> 6858051: Create GC worker threads dynamically
> This change creates a minimal number of GC workers at JVM initialization
> and then adds additional workers as they are needed.  This has been 
> made part of the
> UseDynamicNumberOfGCThreads feature.  When a parallel task is about to
> be executed, the number of workers needed to execute the task is 
> calculated (call
> that number N).  If that number of workers already exist, then no 
> additional workers
> are created.  If fewer than N exists, then additional workers are 
> created.  Workers
> are not destroyed if not needed for the task.
> The UseParallelGC way of executing parallel tasks is different from 
> the other
> collectors so it has a somewhat separate implementation.
> Testing: gc_test_suite with and without UseDynamicNumberOfGCThreads.
> Performance testing with the prototype did not show any regression with
> UseDynamicNumberOfGCThreads turned on.     RBT testing for hotspot_gc
> is in progress.
> Thanks.
> Jon

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