--- a/hotspot/src/share/vm/memory/sharedHeap.hpp Thu Apr 02 16:06:07 2015 +0200
+++ b/hotspot/src/share/vm/memory/sharedHeap.hpp Thu Apr 02 16:07:27 2015 +0200
@@ -27,62 +27,6 @@
#include "gc_interface/collectedHeap.hpp"
-// A "SharedHeap" is an implementation of a java heap for HotSpot. This
-// is an abstract class: there may be many different kinds of heaps. This
-// class defines the functions that a heap must implement, and contains
-// infrastructure common to all heaps.
-
-// Note on use of FlexibleWorkGang's for GC.
-// There are three places where task completion is determined.
-// In
-// 1) ParallelTaskTerminator::offer_termination() where _n_threads
-// must be set to the correct value so that count of workers that
-// have offered termination will exactly match the number
-// working on the task. Tasks such as those derived from GCTask
-// use ParallelTaskTerminator's. Tasks that want load balancing
-// by work stealing use this method to gauge completion.
-// 2) SubTasksDone has a variable _n_threads that is used in
-// all_tasks_completed() to determine completion. all_tasks_complete()
-// counts the number of tasks that have been done and then reset
-// the SubTasksDone so that it can be used again. When the number of
-// tasks is set to the number of GC workers, then _n_threads must
-// be set to the number of active GC workers. G1RootProcessor and
-// GenCollectedHeap have SubTasksDone.
-// 3) SequentialSubTasksDone has an _n_threads that is used in
-// a way similar to SubTasksDone and has the same dependency on the
-// number of active GC workers. CompactibleFreeListSpace and Space
-// have SequentialSubTasksDone's.
-//
-// Examples of using SubTasksDone and SequentialSubTasksDone:
-// G1RootProcessor and GenCollectedHeap::process_roots() use
-// SubTasksDone* _process_strong_tasks to claim tasks for workers
-//
-// GenCollectedHeap::gen_process_roots() calls
-// rem_set()->younger_refs_iterate()
-// to scan the card table and which eventually calls down into
-// CardTableModRefBS::par_non_clean_card_iterate_work(). This method
-// uses SequentialSubTasksDone* _pst to claim tasks.
-// Both SubTasksDone and SequentialSubTasksDone call their method
-// all_tasks_completed() to count the number of GC workers that have
-// finished their work. That logic is "when all the workers are
-// finished the tasks are finished".
-//
-// The pattern that appears in the code is to set _n_threads
-// to a value > 1 before a task that you would like executed in parallel
-// and then to set it to 0 after that task has completed. A value of
-// 0 is a "special" value in set_n_threads() which translates to
-// setting _n_threads to 1.
-//
-// Some code uses _n_termination to decide if work should be done in
-// parallel. The notorious possibly_parallel_oops_do() in threads.cpp
-// is an example of such code. Look for variable "is_par" for other
-// examples.
-//
-// The active_workers is not reset to 0 after a parallel phase. It's
-// value may be used in later phases and in one instance at least
-// (the parallel remark) it has to be used (the parallel remark depends
-// on the partitioning done in the previous parallel scavenge).
-
class SharedHeap : public CollectedHeap {
friend class VMStructs;
@@ -90,48 +34,6 @@
// Full initialization is done in a concrete subtype's "initialize"
// function.
SharedHeap();
-
-public:
- // Note, the below comment needs to be updated to reflect the changes
- // introduced by JDK-8076225. This should be done as part of JDK-8076289.
- //
- //Some collectors will perform "process_strong_roots" in parallel.
- // Such a call will involve claiming some fine-grained tasks, such as
- // scanning of threads. To make this process simpler, we provide the
- // "strong_roots_parity()" method. Collectors that start parallel tasks
- // whose threads invoke "process_strong_roots" must
- // call "change_strong_roots_parity" in sequential code starting such a
- // task. (This also means that a parallel thread may only call
- // process_strong_roots once.)
- //
- // For calls to process_roots by sequential code, the parity is
- // updated automatically.
- //
- // The idea is that objects representing fine-grained tasks, such as
- // threads, will contain a "parity" field. A task will is claimed in the
- // current "process_roots" call only if its parity field is the
- // same as the "strong_roots_parity"; task claiming is accomplished by
- // updating the parity field to the strong_roots_parity with a CAS.
- //
- // If the client meats this spec, then strong_roots_parity() will have
- // the following properties:
- // a) to return a different value than was returned before the last
- // call to change_strong_roots_parity, and
- // c) to never return a distinguished value (zero) with which such
- // task-claiming variables may be initialized, to indicate "never
- // claimed".
- public:
-
- // Call these in sequential code around process_roots.
- // strong_roots_prologue calls change_strong_roots_parity, if
- // parallel tasks are enabled.
- class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {
- SharedHeap* _sh;
-
- public:
- StrongRootsScope(SharedHeap* heap, bool activate = true);
- ~StrongRootsScope();
- };
};
#endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP