1 /* 2 * Copyright (c) 2015, 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_TASKQUEUE_INLINE_HPP 26 #define SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP 27 28 #include "gc/shared/taskqueue.hpp" 29 #include "memory/allocation.inline.hpp" 30 #include "oops/oop.inline.hpp" 31 #include "runtime/atomic.hpp" 32 #include "runtime/orderAccess.inline.hpp" 33 #include "utilities/debug.hpp" 34 #include "utilities/stack.inline.hpp" 35 36 template <class T, MEMFLAGS F> 37 inline GenericTaskQueueSet<T, F>::GenericTaskQueueSet(int n) : _n(n) { 38 typedef T* GenericTaskQueuePtr; 39 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F); 40 for (int i = 0; i < n; i++) { 41 _queues[i] = NULL; 42 } 43 } 44 45 template <class T, MEMFLAGS F> 46 inline GenericTaskQueueSet<T, F>::~GenericTaskQueueSet() { 47 FREE_C_HEAP_ARRAY(T*, _queues); 48 } 49 50 template<class E, MEMFLAGS F, unsigned int N> 51 inline void GenericTaskQueue<E, F, N>::initialize() { 52 _elems = ArrayAllocator<E>::allocate(N, F); 53 } 54 55 template<class E, MEMFLAGS F, unsigned int N> 56 inline GenericTaskQueue<E, F, N>::~GenericTaskQueue() { 57 ArrayAllocator<E>::free(const_cast<E*>(_elems), N); 58 } 59 60 template<class E, MEMFLAGS F, unsigned int N> 61 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) { 62 if (dirty_n_elems == N - 1) { 63 // Actually means 0, so do the push. 64 uint localBot = _bottom; 65 // g++ complains if the volatile result of the assignment is 66 // unused, so we cast the volatile away. We cannot cast directly 67 // to void, because gcc treats that as not using the result of the 68 // assignment. However, casting to E& means that we trigger an 69 // unused-value warning. So, we cast the E& to void. 70 (void)const_cast<E&>(_elems[localBot] = t); 71 OrderAccess::release_store(&_bottom, increment_index(localBot)); 72 TASKQUEUE_STATS_ONLY(stats.record_push()); 73 return true; 74 } 75 return false; 76 } 77 78 template<class E, MEMFLAGS F, unsigned int N> inline bool 79 GenericTaskQueue<E, F, N>::push(E t) { 80 uint localBot = _bottom; 81 assert(localBot < N, "_bottom out of range."); 82 idx_t top = _age.top(); 83 uint dirty_n_elems = dirty_size(localBot, top); 84 assert(dirty_n_elems < N, "n_elems out of range."); 85 if (dirty_n_elems < max_elems()) { 86 // g++ complains if the volatile result of the assignment is 87 // unused, so we cast the volatile away. We cannot cast directly 88 // to void, because gcc treats that as not using the result of the 89 // assignment. However, casting to E& means that we trigger an 90 // unused-value warning. So, we cast the E& to void. 91 (void) const_cast<E&>(_elems[localBot] = t); 92 OrderAccess::release_store(&_bottom, increment_index(localBot)); 93 TASKQUEUE_STATS_ONLY(stats.record_push()); 94 return true; 95 } else { 96 return push_slow(t, dirty_n_elems); 97 } 98 } 99 100 template <class E, MEMFLAGS F, unsigned int N> 101 inline bool OverflowTaskQueue<E, F, N>::push(E t) 102 { 103 if (!taskqueue_t::push(t)) { 104 overflow_stack()->push(t); 105 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size())); 106 } 107 return true; 108 } 109 110 template <class E, MEMFLAGS F, unsigned int N> 111 inline bool OverflowTaskQueue<E, F, N>::try_push_to_taskqueue(E t) { 112 return taskqueue_t::push(t); 113 } 114 115 // pop_local_slow() is done by the owning thread and is trying to 116 // get the last task in the queue. It will compete with pop_global() 117 // that will be used by other threads. The tag age is incremented 118 // whenever the queue goes empty which it will do here if this thread 119 // gets the last task or in pop_global() if the queue wraps (top == 0 120 // and pop_global() succeeds, see pop_global()). 121 template<class E, MEMFLAGS F, unsigned int N> 122 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) { 123 // This queue was observed to contain exactly one element; either this 124 // thread will claim it, or a competing "pop_global". In either case, 125 // the queue will be logically empty afterwards. Create a new Age value 126 // that represents the empty queue for the given value of "_bottom". (We 127 // must also increment "tag" because of the case where "bottom == 1", 128 // "top == 0". A pop_global could read the queue element in that case, 129 // then have the owner thread do a pop followed by another push. Without 130 // the incrementing of "tag", the pop_global's CAS could succeed, 131 // allowing it to believe it has claimed the stale element.) 132 Age newAge((idx_t)localBot, oldAge.tag() + 1); 133 // Perhaps a competing pop_global has already incremented "top", in which 134 // case it wins the element. 135 if (localBot == oldAge.top()) { 136 // No competing pop_global has yet incremented "top"; we'll try to 137 // install new_age, thus claiming the element. 138 Age tempAge = _age.cmpxchg(newAge, oldAge); 139 if (tempAge == oldAge) { 140 // We win. 141 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity"); 142 TASKQUEUE_STATS_ONLY(stats.record_pop_slow()); 143 return true; 144 } 145 } 146 // We lose; a completing pop_global gets the element. But the queue is empty 147 // and top is greater than bottom. Fix this representation of the empty queue 148 // to become the canonical one. 149 _age.set(newAge); 150 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity"); 151 return false; 152 } 153 154 template<class E, MEMFLAGS F, unsigned int N> inline bool 155 GenericTaskQueue<E, F, N>::pop_local(volatile E& t, uint threshold) { 156 uint localBot = _bottom; 157 // This value cannot be N-1. That can only occur as a result of 158 // the assignment to bottom in this method. If it does, this method 159 // resets the size to 0 before the next call (which is sequential, 160 // since this is pop_local.) 161 uint dirty_n_elems = dirty_size(localBot, _age.top()); 162 assert(dirty_n_elems != N - 1, "Shouldn't be possible..."); 163 if (dirty_n_elems <= threshold) return false; 164 localBot = decrement_index(localBot); 165 _bottom = localBot; 166 // This is necessary to prevent any read below from being reordered 167 // before the store just above. 168 OrderAccess::fence(); 169 // g++ complains if the volatile result of the assignment is 170 // unused, so we cast the volatile away. We cannot cast directly 171 // to void, because gcc treats that as not using the result of the 172 // assignment. However, casting to E& means that we trigger an 173 // unused-value warning. So, we cast the E& to void. 174 (void) const_cast<E&>(t = _elems[localBot]); 175 // This is a second read of "age"; the "size()" above is the first. 176 // If there's still at least one element in the queue, based on the 177 // "_bottom" and "age" we've read, then there can be no interference with 178 // a "pop_global" operation, and we're done. 179 idx_t tp = _age.top(); // XXX 180 if (size(localBot, tp) > 0) { 181 assert(dirty_size(localBot, tp) != N - 1, "sanity"); 182 TASKQUEUE_STATS_ONLY(stats.record_pop()); 183 return true; 184 } else { 185 // Otherwise, the queue contained exactly one element; we take the slow 186 // path. 187 return pop_local_slow(localBot, _age.get()); 188 } 189 } 190 191 template <class E, MEMFLAGS F, unsigned int N> 192 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t) 193 { 194 if (overflow_empty()) return false; 195 t = overflow_stack()->pop(); 196 return true; 197 } 198 199 template<class E, MEMFLAGS F, unsigned int N> 200 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) { 201 Age oldAge = _age.get(); 202 // Architectures with weak memory model require a barrier here 203 // to guarantee that bottom is not older than age, 204 // which is crucial for the correctness of the algorithm. 205 #if !(defined SPARC || defined IA32 || defined AMD64) 206 OrderAccess::fence(); 207 #endif 208 uint localBot = OrderAccess::load_acquire(&_bottom); 209 uint n_elems = size(localBot, oldAge.top()); 210 if (n_elems == 0) { 211 return false; 212 } 213 214 // g++ complains if the volatile result of the assignment is 215 // unused, so we cast the volatile away. We cannot cast directly 216 // to void, because gcc treats that as not using the result of the 217 // assignment. However, casting to E& means that we trigger an 218 // unused-value warning. So, we cast the E& to void. 219 (void) const_cast<E&>(t = _elems[oldAge.top()]); 220 Age newAge(oldAge); 221 newAge.increment(); 222 Age resAge = _age.cmpxchg(newAge, oldAge); 223 224 // Note that using "_bottom" here might fail, since a pop_local might 225 // have decremented it. 226 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity"); 227 return resAge == oldAge; 228 } 229 230 template<class T, MEMFLAGS F> bool 231 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) { 232 if (_n > 2) { 233 uint k1 = queue_num; 234 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n; 235 uint k2 = queue_num; 236 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n; 237 // Sample both and try the larger. 238 uint sz1 = _queues[k1]->size(); 239 uint sz2 = _queues[k2]->size(); 240 if (sz2 > sz1) return _queues[k2]->pop_global(t); 241 else return _queues[k1]->pop_global(t); 242 } else if (_n == 2) { 243 // Just try the other one. 244 uint k = (queue_num + 1) % 2; 245 return _queues[k]->pop_global(t); 246 } else { 247 assert(_n == 1, "can't be zero."); 248 return false; 249 } 250 } 251 252 template<class T, MEMFLAGS F> bool 253 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) { 254 for (uint i = 0; i < 2 * _n; i++) { 255 if (steal_best_of_2(queue_num, seed, t)) { 256 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true)); 257 return true; 258 } 259 } 260 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false)); 261 return false; 262 } 263 264 template <unsigned int N, MEMFLAGS F> 265 inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile { 266 return Atomic::cmpxchg(new_age._data, &_data, old_age._data); 267 } 268 269 template<class E, MEMFLAGS F, unsigned int N> 270 template<class Fn> 271 inline void GenericTaskQueue<E, F, N>::iterate(Fn fn) { 272 uint iters = size(); 273 uint index = _bottom; 274 for (uint i = 0; i < iters; ++i) { 275 index = decrement_index(index); 276 fn(const_cast<E&>(_elems[index])); // cast away volatility 277 } 278 } 279 280 281 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP