1 /* 2 * Copyright (c) 2000, 2018, Oracle and/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_SHARED_CARDTABLEMODREFBS_HPP 26 #define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP 27 28 #include "gc/shared/modRefBarrierSet.hpp" 29 #include "utilities/align.hpp" 30 31 class CardTable; 32 33 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and 34 // enumerate ref fields that have been modified (since the last 35 // enumeration.) 36 37 // As it currently stands, this barrier is *imprecise*: when a ref field in 38 // an object "o" is modified, the card table entry for the card containing 39 // the head of "o" is dirtied, not necessarily the card containing the 40 // modified field itself. For object arrays, however, the barrier *is* 41 // precise; only the card containing the modified element is dirtied. 42 // Closures used to scan dirty cards should take these 43 // considerations into account. 44 45 class CardTableModRefBS: public ModRefBarrierSet { 46 // Some classes get to look at some private stuff. 47 friend class VMStructs; 48 protected: 49 50 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 51 // or INCLUDE_JVMCI is being used 52 bool _defer_initial_card_mark; 53 CardTable* _card_table; 54 55 CardTableModRefBS(CardTable* card_table, const BarrierSet::FakeRtti& fake_rtti); 56 57 BarrierSetCodeGen* make_code_gen(); 58 59 public: 60 CardTableModRefBS(CardTable* card_table); 61 ~CardTableModRefBS(); 62 63 CardTable* card_table() const { return _card_table; } 64 65 virtual void initialize(); 66 67 void write_region(MemRegion mr) { 68 invalidate(mr); 69 } 70 71 void write_ref_array_work(MemRegion mr); 72 73 public: 74 // Record a reference update. Note that these versions are precise! 75 // The scanning code has to handle the fact that the write barrier may be 76 // either precise or imprecise. We make non-virtual inline variants of 77 // these functions here for performance. 78 template <DecoratorSet decorators, typename T> 79 void write_ref_field_post(T* field, oop newVal); 80 81 virtual void invalidate(MemRegion mr); 82 83 // ReduceInitialCardMarks 84 void initialize_deferred_card_mark_barriers(); 85 86 // If the CollectedHeap was asked to defer a store barrier above, 87 // this informs it to flush such a deferred store barrier to the 88 // remembered set. 89 void flush_deferred_card_mark_barrier(JavaThread* thread); 90 91 // Can a compiler initialize a new object without store barriers? 92 // This permission only extends from the creation of a new object 93 // via a TLAB up to the first subsequent safepoint. If such permission 94 // is granted for this heap type, the compiler promises to call 95 // defer_store_barrier() below on any slow path allocation of 96 // a new object for which such initializing store barriers will 97 // have been elided. G1, like CMS, allows this, but should be 98 // ready to provide a compensating write barrier as necessary 99 // if that storage came out of a non-young region. The efficiency 100 // of this implementation depends crucially on being able to 101 // answer very efficiently in constant time whether a piece of 102 // storage in the heap comes from a young region or not. 103 // See ReduceInitialCardMarks. 104 virtual bool can_elide_tlab_store_barriers() const { 105 return true; 106 } 107 108 // If a compiler is eliding store barriers for TLAB-allocated objects, 109 // we will be informed of a slow-path allocation by a call 110 // to on_slowpath_allocation_exit() below. Such a call precedes the 111 // initialization of the object itself, and no post-store-barriers will 112 // be issued. Some heap types require that the barrier strictly follows 113 // the initializing stores. (This is currently implemented by deferring the 114 // barrier until the next slow-path allocation or gc-related safepoint.) 115 // This interface answers whether a particular barrier type needs the card 116 // mark to be thus strictly sequenced after the stores. 117 virtual bool card_mark_must_follow_store() const; 118 119 virtual void on_slowpath_allocation_exit(JavaThread* thread, oop new_obj); 120 virtual void on_thread_detach(JavaThread* thread); 121 122 virtual void make_parsable(JavaThread* thread) { flush_deferred_card_mark_barrier(thread); } 123 124 virtual void print_on(outputStream* st) const; 125 126 template <DecoratorSet decorators, typename BarrierSetT = CardTableModRefBS> 127 class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {}; 128 }; 129 130 template<> 131 struct BarrierSet::GetName<CardTableModRefBS> { 132 static const BarrierSet::Name value = BarrierSet::CardTableModRef; 133 }; 134 135 template<> 136 struct BarrierSet::GetType<BarrierSet::CardTableModRef> { 137 typedef CardTableModRefBS type; 138 }; 139 140 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP