1 /* 2 * Copyright (c) 2018, 2019, 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_GC_SHARED_OOPSTORAGEPARSTATE_HPP 26 #define SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP 27 28 #include "gc/shared/oopStorage.hpp" 29 #include "utilities/globalDefinitions.hpp" 30 31 ////////////////////////////////////////////////////////////////////////////// 32 // Support for parallel and optionally concurrent state iteration. 33 // 34 // Concurrent Iteration 35 // 36 // Iteration involves the _active_array (an ActiveArray), which contains all 37 // of the blocks owned by a storage object. 38 // 39 // A concurrent ParState increments the associated storage's 40 // _concurrent_iteration_count when the state is constructed, and 41 // decrements it when the state is destroyed. These assignments are made with 42 // _active_mutex locked. Meanwhile, empty block deletion is not done while 43 // _concurrent_iteration_count is non-zero. The counter check and the dependent 44 // removal of a block from the _active_array is performed with _active_mutex 45 // locked. This prevents concurrent iteration and empty block deletion from 46 // interfering with with each other. 47 // 48 // Both allocate() and delete_empty_blocks() lock the 49 // _allocation_mutex while performing their respective list and array 50 // manipulations, preventing them from interfering with each other. 51 // 52 // When allocate() creates a new block, it is added to the end of the 53 // _active_array. Then _active_array's _block_count is incremented to account 54 // for the new block. When concurrent iteration is started (by a parallel 55 // worker thread calling the state's iterate() function), the current 56 // _active_array and its _block_count are captured for use by the iteration, 57 // with iteration processing all blocks in that array up to that block count. 58 // 59 // As a result, the sequence over which concurrent iteration operates is 60 // stable. However, once the iteration is started, later allocations may add 61 // blocks to the end of the array that won't be examined by the iteration. 62 // An allocation may even require expansion of the array, so the iteration is 63 // no longer processing the current array, but rather the previous one. 64 // And while the sequence is stable, concurrent allocate() and release() 65 // operations may change the set of allocated entries in a block at any time 66 // during the iteration. 67 // 68 // As a result, a concurrent iteration handler must accept that some 69 // allocations and releases that occur after the iteration started will not be 70 // seen by the iteration. Further, some may overlap examination by the 71 // iteration. To help with this, allocate() and release() have an invariant 72 // that an entry's value must be NULL when it is not in use. 73 // 74 // ParState<concurrent, is_const> 75 // concurrent must be true if iteration may be concurrent with the 76 // mutators. 77 // 78 // is_const must be true if the iteration is over a constant storage 79 // object, false if the iteration may modify the storage object. 80 // 81 // ParState([const] OopStorage* storage) 82 // Construct an object for managing an iteration over storage. For a 83 // concurrent ParState, empty block deletion for the associated storage 84 // is inhibited for the life of the ParState. 85 // 86 // template<typename F> void iterate(F f) 87 // Repeatedly claims a block from the associated storage that has 88 // not been processed by this iteration (possibly by other threads), 89 // and applies f to each entry in the claimed block. Assume p is of 90 // type const oop* or oop*, according to is_const. Then f(p) must be 91 // a valid expression whose value is ignored. Concurrent uses must 92 // be prepared for an entry's value to change at any time, due to 93 // mutator activity. 94 // 95 // template<typename Closure> void oops_do(Closure* cl) 96 // Wrapper around iterate, providing an adaptation layer allowing 97 // the use of OopClosures and similar objects for iteration. Assume 98 // p is of type const oop* or oop*, according to is_const. Then 99 // cl->do_oop(p) must be a valid expression whose value is ignored. 100 // Concurrent uses must be prepared for the entry's value to change 101 // at any time, due to mutator activity. 102 // 103 // Optional operations, provided only if !concurrent && !is_const. 104 // These are not provided when is_const, because the storage object 105 // may be modified by the iteration infrastructure, even if the 106 // provided closure doesn't modify the storage object. These are not 107 // provided when concurrent because any pre-filtering behavior by the 108 // iteration infrastructure is inappropriate for concurrent iteration; 109 // modifications of the storage by the mutator could result in the 110 // pre-filtering being applied (successfully or not) to objects that 111 // are unrelated to what the closure finds in the entry. 112 // 113 // template<typename Closure> void weak_oops_do(Closure* cl) 114 // template<typename IsAliveClosure, typename Closure> 115 // void weak_oops_do(IsAliveClosure* is_alive, Closure* cl) 116 // Wrappers around iterate, providing an adaptation layer allowing 117 // the use of is-alive closures and OopClosures for iteration. 118 // Assume p is of type oop*. Then 119 // 120 // - cl->do_oop(p) must be a valid expression whose value is ignored. 121 // 122 // - is_alive->do_object_b(*p) must be a valid expression whose value 123 // is convertible to bool. 124 // 125 // If *p == NULL then neither is_alive nor cl will be invoked for p. 126 // If is_alive->do_object_b(*p) is false, then cl will not be 127 // invoked on p. 128 129 class OopStorage::BasicParState { 130 const OopStorage* _storage; 131 ActiveArray* _active_array; 132 size_t _block_count; 133 volatile size_t _next_block; 134 uint _estimated_thread_count; 135 bool _concurrent; 136 137 NONCOPYABLE(BasicParState); 138 139 struct IterationData; 140 141 void update_concurrent_iteration_count(int value); 142 bool claim_next_segment(IterationData* data); 143 bool finish_iteration(const IterationData* data) const; 144 145 // Wrapper for iteration handler; ignore handler result and return true. 146 template<typename F> class AlwaysTrueFn; 147 148 public: 149 BasicParState(const OopStorage* storage, 150 uint estimated_thread_count, 151 bool concurrent); 152 ~BasicParState(); 153 154 const OopStorage* storage() const { return _storage; } 155 156 template<bool is_const, typename F> void iterate(F f); 157 158 static uint default_estimated_thread_count(bool concurrent); 159 }; 160 161 template<bool concurrent, bool is_const> 162 class OopStorage::ParState { 163 BasicParState _basic_state; 164 165 typedef typename Conditional<is_const, 166 const OopStorage*, 167 OopStorage*>::type StoragePtr; 168 169 public: 170 ParState(StoragePtr storage, 171 uint estimated_thread_count = BasicParState::default_estimated_thread_count(concurrent)) : 172 _basic_state(storage, estimated_thread_count, concurrent) 173 {} 174 175 const OopStorage* storage() const { return _basic_state.storage(); } 176 template<typename F> void iterate(F f); 177 template<typename Closure> void oops_do(Closure* cl); 178 }; 179 180 template<> 181 class OopStorage::ParState<false, false> { 182 BasicParState _basic_state; 183 184 public: 185 ParState(OopStorage* storage, 186 uint estimated_thread_count = BasicParState::default_estimated_thread_count(false)) : 187 _basic_state(storage, estimated_thread_count, false) 188 {} 189 190 const OopStorage* storage() const { return _basic_state.storage(); } 191 template<typename F> void iterate(F f); 192 template<typename Closure> void oops_do(Closure* cl); 193 template<typename Closure> void weak_oops_do(Closure* cl); 194 template<typename IsAliveClosure, typename Closure> 195 void weak_oops_do(IsAliveClosure* is_alive, Closure* cl); 196 }; 197 198 #endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP