500 lines
18 KiB
C++
500 lines
18 KiB
C++
/*
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* Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*
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*/
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// ReferenceProcessor class encapsulates the per-"collector" processing
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// of "weak" references for GC. The interface is useful for supporting
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// a generational abstraction, in particular when there are multiple
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// generations that are being independently collected -- possibly
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// concurrently and/or incrementally. Note, however, that the
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// ReferenceProcessor class abstracts away from a generational setting
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// by using only a heap interval (called "span" below), thus allowing
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// its use in a straightforward manner in a general, non-generational
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// setting.
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//
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// The basic idea is that each ReferenceProcessor object concerns
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// itself with ("weak") reference processing in a specific "span"
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// of the heap of interest to a specific collector. Currently,
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// the span is a convex interval of the heap, but, efficiency
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// apart, there seems to be no reason it couldn't be extended
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// (with appropriate modifications) to any "non-convex interval".
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// forward references
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class ReferencePolicy;
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class AbstractRefProcTaskExecutor;
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class DiscoveredList;
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class ReferenceProcessor : public CHeapObj {
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friend class DiscoveredList;
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friend class DiscoveredListIterator;
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protected:
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// End of list marker
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static oop _sentinelRef;
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MemRegion _span; // (right-open) interval of heap
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// subject to wkref discovery
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bool _discovering_refs; // true when discovery enabled
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bool _discovery_is_atomic; // if discovery is atomic wrt
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// other collectors in configuration
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bool _discovery_is_mt; // true if reference discovery is MT.
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bool _enqueuing_is_done; // true if all weak references enqueued
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bool _processing_is_mt; // true during phases when
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// reference processing is MT.
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int _next_id; // round-robin counter in
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// support of work distribution
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// For collectors that do not keep GC marking information
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// in the object header, this field holds a closure that
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// helps the reference processor determine the reachability
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// of an oop (the field is currently initialized to NULL for
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// all collectors but the CMS collector).
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BoolObjectClosure* _is_alive_non_header;
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// The discovered ref lists themselves
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int _num_q; // the MT'ness degree of the queues below
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DiscoveredList* _discoveredSoftRefs; // pointer to array of oops
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DiscoveredList* _discoveredWeakRefs;
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DiscoveredList* _discoveredFinalRefs;
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DiscoveredList* _discoveredPhantomRefs;
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public:
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int num_q() { return _num_q; }
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DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
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static oop* sentinel_ref() { return &_sentinelRef; }
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public:
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// Process references with a certain reachability level.
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void process_discovered_reflist(DiscoveredList refs_lists[],
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ReferencePolicy* policy,
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bool clear_referent,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc,
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AbstractRefProcTaskExecutor* task_executor);
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void process_phaseJNI(BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc);
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// Work methods used by the method process_discovered_reflist
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// Phase1: keep alive all those referents that are otherwise
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// dead but which must be kept alive by policy (and their closure).
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void process_phase1(DiscoveredList& refs_list_addr,
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ReferencePolicy* policy,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc);
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// Phase2: remove all those references whose referents are
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// reachable.
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inline void process_phase2(DiscoveredList& refs_list_addr,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc) {
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if (discovery_is_atomic()) {
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// complete_gc is ignored in this case for this phase
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pp2_work(refs_list_addr, is_alive, keep_alive);
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} else {
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assert(complete_gc != NULL, "Error");
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pp2_work_concurrent_discovery(refs_list_addr, is_alive,
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keep_alive, complete_gc);
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}
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}
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// Work methods in support of process_phase2
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void pp2_work(DiscoveredList& refs_list_addr,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive);
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void pp2_work_concurrent_discovery(
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DiscoveredList& refs_list_addr,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc);
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// Phase3: process the referents by either clearing them
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// or keeping them alive (and their closure)
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void process_phase3(DiscoveredList& refs_list_addr,
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bool clear_referent,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc);
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// Enqueue references with a certain reachability level
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void enqueue_discovered_reflist(DiscoveredList& refs_list, oop* pending_list_addr);
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// "Preclean" all the discovered reference lists
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// by removing references with strongly reachable referents.
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// The first argument is a predicate on an oop that indicates
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// its (strong) reachability and the second is a closure that
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// may be used to incrementalize or abort the precleaning process.
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// The caller is responsible for taking care of potential
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// interference with concurrent operations on these lists
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// (or predicates involved) by other threads. Currently
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// only used by the CMS collector.
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void preclean_discovered_references(BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc,
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YieldClosure* yield);
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// Delete entries in the discovered lists that have
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// either a null referent or are not active. Such
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// Reference objects can result from the clearing
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// or enqueueing of Reference objects concurrent
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// with their discovery by a (concurrent) collector.
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// For a definition of "active" see java.lang.ref.Reference;
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// Refs are born active, become inactive when enqueued,
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// and never become active again. The state of being
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// active is encoded as follows: A Ref is active
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// if and only if its "next" field is NULL.
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void clean_up_discovered_references();
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void clean_up_discovered_reflist(DiscoveredList& refs_list);
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// Returns the name of the discovered reference list
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// occupying the i / _num_q slot.
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const char* list_name(int i);
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protected:
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// "Preclean" the given discovered reference list
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// by removing references with strongly reachable referents.
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// Currently used in support of CMS only.
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void preclean_discovered_reflist(DiscoveredList& refs_list,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc,
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YieldClosure* yield);
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void enqueue_discovered_reflists(oop* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
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int next_id() {
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int id = _next_id;
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if (++_next_id == _num_q) {
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_next_id = 0;
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}
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return id;
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}
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DiscoveredList* get_discovered_list(ReferenceType rt);
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inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
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oop* discovered_addr);
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void verify_ok_to_handle_reflists() PRODUCT_RETURN;
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void abandon_partial_discovered_list(DiscoveredList& refs_list);
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void abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]);
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// Calculate the number of jni handles.
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unsigned int count_jni_refs();
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// Balances reference queues.
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void balance_queues(DiscoveredList ref_lists[]);
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// Update (advance) the soft ref master clock field.
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void update_soft_ref_master_clock();
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public:
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// constructor
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ReferenceProcessor():
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_span((HeapWord*)NULL, (HeapWord*)NULL),
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_discoveredSoftRefs(NULL), _discoveredWeakRefs(NULL),
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_discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
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_discovering_refs(false),
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_discovery_is_atomic(true),
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_enqueuing_is_done(false),
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_discovery_is_mt(false),
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_is_alive_non_header(NULL),
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_num_q(0),
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_processing_is_mt(false),
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_next_id(0)
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{}
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ReferenceProcessor(MemRegion span, bool atomic_discovery,
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bool mt_discovery, int mt_degree = 1,
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bool mt_processing = false);
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// Allocates and initializes a reference processor.
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static ReferenceProcessor* create_ref_processor(
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MemRegion span,
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bool atomic_discovery,
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bool mt_discovery,
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BoolObjectClosure* is_alive_non_header = NULL,
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int parallel_gc_threads = 1,
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bool mt_processing = false);
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// RefDiscoveryPolicy values
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enum {
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ReferenceBasedDiscovery = 0,
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ReferentBasedDiscovery = 1
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};
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static void init_statics();
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public:
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// get and set "is_alive_non_header" field
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BoolObjectClosure* is_alive_non_header() {
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return _is_alive_non_header;
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}
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void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
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_is_alive_non_header = is_alive_non_header;
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}
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// get and set span
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MemRegion span() { return _span; }
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void set_span(MemRegion span) { _span = span; }
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// start and stop weak ref discovery
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void enable_discovery() { _discovering_refs = true; }
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void disable_discovery() { _discovering_refs = false; }
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bool discovery_enabled() { return _discovering_refs; }
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// whether discovery is atomic wrt other collectors
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bool discovery_is_atomic() const { return _discovery_is_atomic; }
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void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
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// whether discovery is done by multiple threads same-old-timeously
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bool discovery_is_mt() const { return _discovery_is_mt; }
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void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
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// Whether we are in a phase when _processing_ is MT.
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bool processing_is_mt() const { return _processing_is_mt; }
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void set_mt_processing(bool mt) { _processing_is_mt = mt; }
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// whether all enqueuing of weak references is complete
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bool enqueuing_is_done() { return _enqueuing_is_done; }
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void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
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// iterate over oops
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void weak_oops_do(OopClosure* f); // weak roots
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static void oops_do(OopClosure* f); // strong root(s)
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// Discover a Reference object, using appropriate discovery criteria
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bool discover_reference(oop obj, ReferenceType rt);
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// Process references found during GC (called by the garbage collector)
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void process_discovered_references(ReferencePolicy* policy,
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc,
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AbstractRefProcTaskExecutor* task_executor);
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public:
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// Enqueue references at end of GC (called by the garbage collector)
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bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
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// debugging
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void verify_no_references_recorded() PRODUCT_RETURN;
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static void verify();
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// clear the discovered lists (unlinking each entry).
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void clear_discovered_references() PRODUCT_RETURN;
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};
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// A utility class to disable reference discovery in
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// the scope which contains it, for given ReferenceProcessor.
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class NoRefDiscovery: StackObj {
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private:
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ReferenceProcessor* _rp;
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bool _was_discovering_refs;
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public:
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NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
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if (_was_discovering_refs = _rp->discovery_enabled()) {
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_rp->disable_discovery();
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}
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}
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~NoRefDiscovery() {
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if (_was_discovering_refs) {
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_rp->enable_discovery();
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}
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}
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};
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// A utility class to temporarily mutate the span of the
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// given ReferenceProcessor in the scope that contains it.
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class ReferenceProcessorSpanMutator: StackObj {
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private:
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ReferenceProcessor* _rp;
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MemRegion _saved_span;
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public:
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ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
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MemRegion span):
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_rp(rp) {
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_saved_span = _rp->span();
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_rp->set_span(span);
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}
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~ReferenceProcessorSpanMutator() {
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_rp->set_span(_saved_span);
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}
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};
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// A utility class to temporarily change the MT'ness of
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// reference discovery for the given ReferenceProcessor
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// in the scope that contains it.
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class ReferenceProcessorMTMutator: StackObj {
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private:
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ReferenceProcessor* _rp;
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bool _saved_mt;
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public:
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ReferenceProcessorMTMutator(ReferenceProcessor* rp,
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bool mt):
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_rp(rp) {
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_saved_mt = _rp->discovery_is_mt();
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_rp->set_mt_discovery(mt);
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}
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~ReferenceProcessorMTMutator() {
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_rp->set_mt_discovery(_saved_mt);
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}
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};
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// A utility class to temporarily change the disposition
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// of the "is_alive_non_header" closure field of the
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// given ReferenceProcessor in the scope that contains it.
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class ReferenceProcessorIsAliveMutator: StackObj {
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private:
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ReferenceProcessor* _rp;
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BoolObjectClosure* _saved_cl;
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public:
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ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
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BoolObjectClosure* cl):
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_rp(rp) {
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_saved_cl = _rp->is_alive_non_header();
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_rp->set_is_alive_non_header(cl);
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}
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~ReferenceProcessorIsAliveMutator() {
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_rp->set_is_alive_non_header(_saved_cl);
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}
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};
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// A utility class to temporarily change the disposition
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// of the "discovery_is_atomic" field of the
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// given ReferenceProcessor in the scope that contains it.
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class ReferenceProcessorAtomicMutator: StackObj {
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private:
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ReferenceProcessor* _rp;
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bool _saved_atomic_discovery;
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public:
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ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
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bool atomic):
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_rp(rp) {
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_saved_atomic_discovery = _rp->discovery_is_atomic();
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_rp->set_atomic_discovery(atomic);
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}
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~ReferenceProcessorAtomicMutator() {
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_rp->set_atomic_discovery(_saved_atomic_discovery);
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}
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};
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// A utility class to temporarily change the MT processing
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// disposition of the given ReferenceProcessor instance
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// in the scope that contains it.
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class ReferenceProcessorMTProcMutator: StackObj {
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private:
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ReferenceProcessor* _rp;
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bool _saved_mt;
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public:
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ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
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bool mt):
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_rp(rp) {
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_saved_mt = _rp->processing_is_mt();
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_rp->set_mt_processing(mt);
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}
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~ReferenceProcessorMTProcMutator() {
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_rp->set_mt_processing(_saved_mt);
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}
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};
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// This class is an interface used to implement task execution for the
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// reference processing.
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class AbstractRefProcTaskExecutor {
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public:
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// Abstract tasks to execute.
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class ProcessTask;
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class EnqueueTask;
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// Executes a task using worker threads.
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virtual void execute(ProcessTask& task) = 0;
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virtual void execute(EnqueueTask& task) = 0;
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// Switch to single threaded mode.
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virtual void set_single_threaded_mode() { };
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};
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// Abstract reference processing task to execute.
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class AbstractRefProcTaskExecutor::ProcessTask {
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protected:
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ProcessTask(ReferenceProcessor& ref_processor,
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DiscoveredList refs_lists[],
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bool marks_oops_alive)
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: _ref_processor(ref_processor),
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_refs_lists(refs_lists),
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_marks_oops_alive(marks_oops_alive)
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{ }
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public:
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virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
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OopClosure& keep_alive,
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VoidClosure& complete_gc) = 0;
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// Returns true if a task marks some oops as alive.
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bool marks_oops_alive() const
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{ return _marks_oops_alive; }
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protected:
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ReferenceProcessor& _ref_processor;
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DiscoveredList* _refs_lists;
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const bool _marks_oops_alive;
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};
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// Abstract reference processing task to execute.
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class AbstractRefProcTaskExecutor::EnqueueTask {
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protected:
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EnqueueTask(ReferenceProcessor& ref_processor,
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DiscoveredList refs_lists[],
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oop* pending_list_addr,
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oop sentinel_ref,
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int n_queues)
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: _ref_processor(ref_processor),
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_refs_lists(refs_lists),
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_pending_list_addr(pending_list_addr),
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_sentinel_ref(sentinel_ref),
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_n_queues(n_queues)
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{ }
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public:
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virtual void work(unsigned int work_id) = 0;
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protected:
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ReferenceProcessor& _ref_processor;
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DiscoveredList* _refs_lists;
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oop* _pending_list_addr;
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oop _sentinel_ref;
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int _n_queues;
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};
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