--- old/src/share/vm/memory/sharedHeap.hpp 2015-04-02 12:41:39.472299895 +0200 +++ new/src/share/vm/memory/sharedHeap.hpp 2015-04-02 12:41:39.360299900 +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; @@ -90,46 +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 { - public: - StrongRootsScope(bool activate = true); - ~StrongRootsScope(); - }; }; #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP