1 /* 2 * Copyright (c) 2021, Amazon.com, Inc. or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP 26 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP 27 28 #include "gc/shenandoah/shenandoahGeneration.hpp" 29 30 class ShenandoahHeapRegion; 31 class ShenandoahHeapRegionClosure; 32 33 class ShenandoahOldGeneration : public ShenandoahGeneration { 34 public: 35 ShenandoahOldGeneration(uint max_queues, size_t max_capacity, size_t soft_max_capacity); 36 37 const char* name() const override; 38 39 bool contains(ShenandoahHeapRegion* region) const override; 40 41 bool contains(oop obj) const override; 42 43 void parallel_heap_region_iterate(ShenandoahHeapRegionClosure* cl) override; 44 45 void heap_region_iterate(ShenandoahHeapRegionClosure* cl) override; 46 47 void set_concurrent_mark_in_progress(bool in_progress) override; 48 49 virtual void cancel_marking() override; 50 51 void prepare_regions_and_collection_set(bool concurrent) override; 52 53 virtual ShenandoahHeuristics* initialize_heuristics(ShenandoahMode* gc_mode) override; 54 55 // We leave the SATB barrier on for the entirety of the old generation 56 // marking phase. In some cases, this can cause a write to a perfectly 57 // reachable oop to enqueue a pointer that later becomes garbage (because 58 // it points at an object in the collection set, for example). There are 59 // also cases where the referent of a weak reference ends up in the SATB 60 // and is later collected. In these cases the oop in the SATB buffer becomes 61 // invalid and the _next_ cycle will crash during its marking phase. To 62 // avoid this problem, we "purge" the SATB buffers during the final update 63 // references phase if (and only if) an old generation mark is in progress. 64 // At this stage we can safely determine if any of the oops in the SATB 65 // buffer belong to trashed regions (before they are recycled). As it 66 // happens, flushing a SATB queue also filters out oops which have already 67 // been marked - which is the case for anything that is being evacuated 68 // from the collection set. 69 // 70 // Alternatively, we could inspect the state of the heap and the age of the 71 // object at the barrier, but we reject this approach because it is likely 72 // the performance impact would be too severe. 73 void transfer_pointers_from_satb(); 74 75 bool is_concurrent_mark_in_progress() override; 76 }; 77 78 79 #endif //SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP