1 /*
2 * Copyright (c) 2015, 2016, 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.
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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
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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 E, MEMFLAGS F, unsigned int N>
46 inline void GenericTaskQueue<E, F, N>::initialize() {
47 _elems = ArrayAllocator<E>::allocate(N, F);
48 }
49
50 template<class E, MEMFLAGS F, unsigned int N>
51 inline GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
52 assert(false, "This code is currently never called");
53 ArrayAllocator<E>::free(const_cast<E*>(_elems), N);
54 }
55
56 template<class E, MEMFLAGS F, unsigned int N>
57 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
58 if (dirty_n_elems == N - 1) {
59 // Actually means 0, so do the push.
60 uint localBot = _bottom;
61 // g++ complains if the volatile result of the assignment is
62 // unused, so we cast the volatile away. We cannot cast directly
63 // to void, because gcc treats that as not using the result of the
64 // assignment. However, casting to E& means that we trigger an
65 // unused-value warning. So, we cast the E& to void.
66 (void)const_cast<E&>(_elems[localBot] = t);
67 OrderAccess::release_store(&_bottom, increment_index(localBot));
68 TASKQUEUE_STATS_ONLY(stats.record_push());
69 return true;
70 }
71 return false;
72 }
73
74 template<class E, MEMFLAGS F, unsigned int N> inline bool
75 GenericTaskQueue<E, F, N>::push(E t) {
76 uint localBot = _bottom;
77 assert(localBot < N, "_bottom out of range.");
78 idx_t top = _age.top();
79 uint dirty_n_elems = dirty_size(localBot, top);
80 assert(dirty_n_elems < N, "n_elems out of range.");
81 if (dirty_n_elems < max_elems()) {
82 // g++ complains if the volatile result of the assignment is
83 // unused, so we cast the volatile away. We cannot cast directly
84 // to void, because gcc treats that as not using the result of the
85 // assignment. However, casting to E& means that we trigger an
86 // unused-value warning. So, we cast the E& to void.
87 (void) const_cast<E&>(_elems[localBot] = t);
88 OrderAccess::release_store(&_bottom, increment_index(localBot));
89 TASKQUEUE_STATS_ONLY(stats.record_push());
90 return true;
91 } else {
92 return push_slow(t, dirty_n_elems);
93 }
94 }
95
96 template <class E, MEMFLAGS F, unsigned int N>
97 inline bool OverflowTaskQueue<E, F, N>::push(E t)
98 {
99 if (!taskqueue_t::push(t)) {
100 overflow_stack()->push(t);
101 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
102 }
103 return true;
104 }
105
106 template <class E, MEMFLAGS F, unsigned int N>
107 inline bool OverflowTaskQueue<E, F, N>::try_push_to_taskqueue(E t) {
108 return taskqueue_t::push(t);
109 }
110
111 // pop_local_slow() is done by the owning thread and is trying to
112 // get the last task in the queue. It will compete with pop_global()
113 // that will be used by other threads. The tag age is incremented
114 // whenever the queue goes empty which it will do here if this thread
115 // gets the last task or in pop_global() if the queue wraps (top == 0
116 // and pop_global() succeeds, see pop_global()).
117 template<class E, MEMFLAGS F, unsigned int N>
118 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
119 // This queue was observed to contain exactly one element; either this
120 // thread will claim it, or a competing "pop_global". In either case,
121 // the queue will be logically empty afterwards. Create a new Age value
122 // that represents the empty queue for the given value of "_bottom". (We
123 // must also increment "tag" because of the case where "bottom == 1",
124 // "top == 0". A pop_global could read the queue element in that case,
125 // then have the owner thread do a pop followed by another push. Without
126 // the incrementing of "tag", the pop_global's CAS could succeed,
127 // allowing it to believe it has claimed the stale element.)
128 Age newAge((idx_t)localBot, oldAge.tag() + 1);
129 // Perhaps a competing pop_global has already incremented "top", in which
130 // case it wins the element.
131 if (localBot == oldAge.top()) {
132 // No competing pop_global has yet incremented "top"; we'll try to
133 // install new_age, thus claiming the element.
134 Age tempAge = _age.cmpxchg(newAge, oldAge);
135 if (tempAge == oldAge) {
136 // We win.
137 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
138 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
139 return true;
140 }
141 }
142 // We lose; a completing pop_global gets the element. But the queue is empty
143 // and top is greater than bottom. Fix this representation of the empty queue
144 // to become the canonical one.
145 _age.set(newAge);
146 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
147 return false;
148 }
149
150 template<class E, MEMFLAGS F, unsigned int N> inline bool
151 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
152 uint localBot = _bottom;
153 // This value cannot be N-1. That can only occur as a result of
154 // the assignment to bottom in this method. If it does, this method
155 // resets the size to 0 before the next call (which is sequential,
156 // since this is pop_local.)
157 uint dirty_n_elems = dirty_size(localBot, _age.top());
158 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
159 if (dirty_n_elems == 0) return false;
160 localBot = decrement_index(localBot);
161 _bottom = localBot;
162 // This is necessary to prevent any read below from being reordered
163 // before the store just above.
164 OrderAccess::fence();
165 // g++ complains if the volatile result of the assignment is
166 // unused, so we cast the volatile away. We cannot cast directly
167 // to void, because gcc treats that as not using the result of the
168 // assignment. However, casting to E& means that we trigger an
169 // unused-value warning. So, we cast the E& to void.
170 (void) const_cast<E&>(t = _elems[localBot]);
171 // This is a second read of "age"; the "size()" above is the first.
172 // If there's still at least one element in the queue, based on the
173 // "_bottom" and "age" we've read, then there can be no interference with
174 // a "pop_global" operation, and we're done.
175 idx_t tp = _age.top(); // XXX
176 if (size(localBot, tp) > 0) {
177 assert(dirty_size(localBot, tp) != N - 1, "sanity");
178 TASKQUEUE_STATS_ONLY(stats.record_pop());
179 return true;
180 } else {
181 // Otherwise, the queue contained exactly one element; we take the slow
182 // path.
183 return pop_local_slow(localBot, _age.get());
184 }
185 }
186
187 template <class E, MEMFLAGS F, unsigned int N>
188 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
189 {
190 if (overflow_empty()) return false;
191 t = overflow_stack()->pop();
192 return true;
193 }
194
195 template<class E, MEMFLAGS F, unsigned int N>
196 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
197 Age oldAge = _age.get();
198 // Architectures with weak memory model require a barrier here
199 // to guarantee that bottom is not older than age,
200 // which is crucial for the correctness of the algorithm.
201 #if !(defined SPARC || defined IA32 || defined AMD64)
202 OrderAccess::fence();
203 #endif
204 uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
205 uint n_elems = size(localBot, oldAge.top());
206 if (n_elems == 0) {
207 return false;
208 }
209
210 // g++ complains if the volatile result of the assignment is
211 // unused, so we cast the volatile away. We cannot cast directly
212 // to void, because gcc treats that as not using the result of the
213 // assignment. However, casting to E& means that we trigger an
214 // unused-value warning. So, we cast the E& to void.
215 (void) const_cast<E&>(t = _elems[oldAge.top()]);
216 Age newAge(oldAge);
217 newAge.increment();
218 Age resAge = _age.cmpxchg(newAge, oldAge);
219
220 // Note that using "_bottom" here might fail, since a pop_local might
221 // have decremented it.
222 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
223 return resAge == oldAge;
224 }
225
226 template<class T, MEMFLAGS F> bool
227 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
228 if (_n > 2) {
229 uint k1 = queue_num;
230 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
231 uint k2 = queue_num;
232 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
233 // Sample both and try the larger.
234 uint sz1 = _queues[k1]->size();
235 uint sz2 = _queues[k2]->size();
236 if (sz2 > sz1) return _queues[k2]->pop_global(t);
237 else return _queues[k1]->pop_global(t);
238 } else if (_n == 2) {
239 // Just try the other one.
240 uint k = (queue_num + 1) % 2;
241 return _queues[k]->pop_global(t);
242 } else {
243 assert(_n == 1, "can't be zero.");
244 return false;
245 }
246 }
247
248 template<class T, MEMFLAGS F> bool
249 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
250 for (uint i = 0; i < 2 * _n; i++) {
251 if (steal_best_of_2(queue_num, seed, t)) {
252 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
253 return true;
254 }
255 }
256 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
257 return false;
258 }
259
260 template <unsigned int N, MEMFLAGS F>
261 inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile {
262 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
263 (volatile intptr_t *)&_data,
264 (intptr_t)old_age._data);
265 }
266
267 template<class E, MEMFLAGS F, unsigned int N>
268 template<class Fn>
269 inline void GenericTaskQueue<E, F, N>::iterate(Fn fn) {
270 uint iters = size();
271 uint index = _bottom;
272 for (uint i = 0; i < iters; ++i) {
273 index = decrement_index(index);
274 fn(const_cast<E&>(_elems[index])); // cast away volatility
275 }
276 }
277
278
279 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP