1 /* 2 * Copyright (c) 2014, 2018, Red Hat, Inc. All rights reserved. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. 7 * 8 * This code is distributed in the hope that it will be useful, but WITHOUT 9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 11 * version 2 for more details (a copy is included in the LICENSE file that 12 * accompanied this code). 13 * 14 * You should have received a copy of the GNU General Public License version 15 * 2 along with this work; if not, write to the Free Software Foundation, 16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 17 * 18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 19 * or visit www.oracle.com if you need additional information or have any 20 * questions. 21 * 22 */ 23 24 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP 25 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP 26 27 #include "gc/shared/gcTimer.hpp" 28 #include "gc/shenandoah/shenandoahHeap.hpp" 29 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp" 30 31 /** 32 * This implements Full GC (e.g. when invoking System.gc()) using a mark-compact algorithm. 33 * 34 * Current implementation is parallel sliding Lisp-2-style algorithm, based on 35 * "Parallel Garbage Collection for Shared Memory Multiprocessors", by Christine Flood et al. 36 * http://people.csail.mit.edu/shanir/publications/dfsz2001.pdf 37 * 38 * It is implemented in four phases: 39 * 40 * 1. Mark all live objects of the heap by traversing objects starting at GC roots. 41 * 2. Calculate the new location of each live object. This is done by sequentially scanning 42 * the heap, keeping track of a next-location-pointer, which is then written to each 43 * object's fwdptr field. 44 * 3. Update all references. This is implemented by another scan of the heap, and updates 45 * all references in live objects by what's stored in the target object's fwdptr. 46 * 4. Compact the heap by copying all live objects to their new location. 47 * 48 * Parallelization is handled by assigning each GC worker the slice of the heap (the set of regions) 49 * where it does sliding compaction, without interfering with other threads. 50 */ 51 52 class ShenandoahMarkCompact : public CHeapObj<mtGC> { 53 private: 54 GCTimer* _gc_timer; 55 56 public: 57 void initialize(GCTimer* gc_timer); 58 void do_it(GCCause::Cause gc_cause); 59 60 private: 61 void phase1_mark_heap(); 62 void phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices); 63 void phase3_update_references(); 64 void phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices); 65 66 void calculate_target_humongous_objects(); 67 void compact_humongous_objects(); 68 69 }; 70 71 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHMARKCOMPACT_HPP