1 /* 2 * Copyright (c) 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_GC_SHARED_OOPSTORAGEPARSTATE_HPP 26 #define SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP 27 28 #include "gc/shared/oopStorage.hpp" 29 #include "utilities/macros.hpp" 30 31 ////////////////////////////////////////////////////////////////////////////// 32 // Support for parallel and optionally concurrent state iteration. 33 // 34 // Parallel iteration is for the exclusive use of the GC. Other iteration 35 // clients must use serial iteration. 36 // 37 // Concurrent Iteration 38 // 39 // Iteration involves the _active_array (an ActiveArray), which contains all 40 // of the blocks owned by a storage object. 41 // 42 // At most one concurrent ParState can exist at a time for a given storage 43 // object. 44 // 45 // A concurrent ParState sets the associated storage's 46 // _concurrent_iteration_active flag true when the state is constructed, and 47 // sets it false when the state is destroyed. These assignments are made with 48 // _active_mutex locked. Meanwhile, empty block deletion is not done while 49 // _concurrent_iteration_active is true. The flag check and the dependent 50 // removal of a block from the _active_array is performed with _active_mutex 51 // locked. This prevents concurrent iteration and empty block deletion from 52 // interfering with with each other. 53 // 54 // Both allocate() and delete_empty_blocks_concurrent() lock the 55 // _allocation_mutex while performing their respective list and array 56 // manipulations, preventing them from interfering with each other. 57 // 58 // When allocate() creates a new block, it is added to the end of the 59 // _active_array. Then _active_array's _block_count is incremented to account 60 // for the new block. When concurrent iteration is started (by a parallel 61 // worker thread calling the state's iterate() function), the current 62 // _active_array and its _block_count are captured for use by the iteration, 63 // with iteration processing all blocks in that array up to that block count. 64 // 65 // As a result, the sequence over which concurrent iteration operates is 66 // stable. However, once the iteration is started, later allocations may add 67 // blocks to the end of the array that won't be examined by the iteration. 68 // An allocation may even require expansion of the array, so the iteration is 69 // no longer processing the current array, but rather the previous one. 70 // And while the sequence is stable, concurrent allocate() and release() 71 // operations may change the set of allocated entries in a block at any time 72 // during the iteration. 73 // 74 // As a result, a concurrent iteration handler must accept that some 75 // allocations and releases that occur after the iteration started will not be 76 // seen by the iteration. Further, some may overlap examination by the 77 // iteration. To help with this, allocate() and release() have an invariant 78 // that an entry's value must be NULL when it is not in use. 79 // 80 // An in-progress delete_empty_blocks_concurrent() operation can contend with 81 // the start of a concurrent iteration over the _active_mutex. Since both are 82 // under GC control, that potential contention can be eliminated by never 83 // scheduling both operations to run at the same time. 84 // 85 // ParState<concurrent, is_const> 86 // concurrent must be true if iteration is concurrent with the 87 // mutator, false if iteration is at a safepoint. 88 // 89 // is_const must be true if the iteration is over a constant storage 90 // object, false if the iteration may modify the storage object. 91 // 92 // ParState([const] OopStorage* storage) 93 // Construct an object for managing an iteration over storage. For a 94 // concurrent ParState, empty block deletion for the associated storage 95 // is inhibited for the life of the ParState. There can be no more 96 // than one live concurrent ParState at a time for a given storage object. 97 // 98 // template<typename F> void iterate(F f) 99 // Repeatedly claims a block from the associated storage that has 100 // not been processed by this iteration (possibly by other threads), 101 // and applies f to each entry in the claimed block. Assume p is of 102 // type const oop* or oop*, according to is_const. Then f(p) must be 103 // a valid expression whose value is ignored. Concurrent uses must 104 // be prepared for an entry's value to change at any time, due to 105 // mutator activity. 106 // 107 // template<typename Closure> void oops_do(Closure* cl) 108 // Wrapper around iterate, providing an adaptation layer allowing 109 // the use of OopClosures and similar objects for iteration. Assume 110 // p is of type const oop* or oop*, according to is_const. Then 111 // cl->do_oop(p) must be a valid expression whose value is ignored. 112 // Concurrent uses must be prepared for the entry's value to change 113 // at any time, due to mutator activity. 114 // 115 // Optional operations, provided only if !concurrent && !is_const. 116 // These are not provided when is_const, because the storage object 117 // may be modified by the iteration infrastructure, even if the 118 // provided closure doesn't modify the storage object. These are not 119 // provided when concurrent because any pre-filtering behavior by the 120 // iteration infrastructure is inappropriate for concurrent iteration; 121 // modifications of the storage by the mutator could result in the 122 // pre-filtering being applied (successfully or not) to objects that 123 // are unrelated to what the closure finds in the entry. 124 // 125 // template<typename Closure> void weak_oops_do(Closure* cl) 126 // template<typename IsAliveClosure, typename Closure> 127 // void weak_oops_do(IsAliveClosure* is_alive, Closure* cl) 128 // Wrappers around iterate, providing an adaptation layer allowing 129 // the use of is-alive closures and OopClosures for iteration. 130 // Assume p is of type oop*. Then 131 // 132 // - cl->do_oop(p) must be a valid expression whose value is ignored. 133 // 134 // - is_alive->do_object_b(*p) must be a valid expression whose value 135 // is convertible to bool. 136 // 137 // If *p == NULL then neither is_alive nor cl will be invoked for p. 138 // If is_alive->do_object_b(*p) is false, then cl will not be 139 // invoked on p. 140 141 class OopStorage::BasicParState { 142 const OopStorage* _storage; 143 ActiveArray* _active_array; 144 size_t _block_count; 145 volatile size_t _next_block; 146 uint _estimated_thread_count; 147 bool _concurrent; 148 149 // Noncopyable. 150 BasicParState(const BasicParState&); 151 BasicParState& operator=(const BasicParState&); 152 153 struct IterationData; 154 155 void update_iteration_state(bool value); 156 bool claim_next_segment(IterationData* data); 157 bool finish_iteration(const IterationData* data) const; 158 159 // Wrapper for iteration handler; ignore handler result and return true. 160 template<typename F> class AlwaysTrueFn; 161 162 public: 163 BasicParState(const OopStorage* storage, 164 uint estimated_thread_count, 165 bool concurrent); 166 ~BasicParState(); 167 168 template<bool is_const, typename F> void iterate(F f); 169 170 static uint default_estimated_thread_count(bool concurrent); 171 }; 172 173 template<bool concurrent, bool is_const> 174 class OopStorage::ParState { 175 BasicParState _basic_state; 176 177 typedef typename Conditional<is_const, 178 const OopStorage*, 179 OopStorage*>::type StoragePtr; 180 181 public: 182 ParState(StoragePtr storage, 183 uint estimated_thread_count = BasicParState::default_estimated_thread_count(concurrent)) : 184 _basic_state(storage, estimated_thread_count, concurrent) 185 {} 186 187 template<typename F> void iterate(F f); 188 template<typename Closure> void oops_do(Closure* cl); 189 }; 190 191 template<> 192 class OopStorage::ParState<false, false> { 193 BasicParState _basic_state; 194 195 public: 196 ParState(OopStorage* storage, 197 uint estimated_thread_count = BasicParState::default_estimated_thread_count(false)) : 198 _basic_state(storage, estimated_thread_count, false) 199 {} 200 201 template<typename F> void iterate(F f); 202 template<typename Closure> void oops_do(Closure* cl); 203 template<typename Closure> void weak_oops_do(Closure* cl); 204 template<typename IsAliveClosure, typename Closure> 205 void weak_oops_do(IsAliveClosure* is_alive, Closure* cl); 206 }; 207 208 #endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP