1 /*
2 * Copyright (c) 2015, 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.
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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.inline.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, F>::allocate(N);
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, F>::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 // pop_local_slow() is done by the owning thread and is trying to
107 // get the last task in the queue. It will compete with pop_global()
108 // that will be used by other threads. The tag age is incremented
109 // whenever the queue goes empty which it will do here if this thread
110 // gets the last task or in pop_global() if the queue wraps (top == 0
111 // and pop_global() succeeds, see pop_global()).
112 template<class E, MEMFLAGS F, unsigned int N>
113 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
114 // This queue was observed to contain exactly one element; either this
115 // thread will claim it, or a competing "pop_global". In either case,
116 // the queue will be logically empty afterwards. Create a new Age value
117 // that represents the empty queue for the given value of "_bottom". (We
118 // must also increment "tag" because of the case where "bottom == 1",
119 // "top == 0". A pop_global could read the queue element in that case,
120 // then have the owner thread do a pop followed by another push. Without
121 // the incrementing of "tag", the pop_global's CAS could succeed,
122 // allowing it to believe it has claimed the stale element.)
123 Age newAge((idx_t)localBot, oldAge.tag() + 1);
124 // Perhaps a competing pop_global has already incremented "top", in which
125 // case it wins the element.
126 if (localBot == oldAge.top()) {
127 // No competing pop_global has yet incremented "top"; we'll try to
128 // install new_age, thus claiming the element.
129 Age tempAge = _age.cmpxchg(newAge, oldAge);
130 if (tempAge == oldAge) {
131 // We win.
132 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
133 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
134 return true;
135 }
136 }
137 // We lose; a completing pop_global gets the element. But the queue is empty
138 // and top is greater than bottom. Fix this representation of the empty queue
139 // to become the canonical one.
140 _age.set(newAge);
141 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
142 return false;
143 }
144
145 template<class E, MEMFLAGS F, unsigned int N> inline bool
146 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
147 uint localBot = _bottom;
148 // This value cannot be N-1. That can only occur as a result of
149 // the assignment to bottom in this method. If it does, this method
150 // resets the size to 0 before the next call (which is sequential,
151 // since this is pop_local.)
152 uint dirty_n_elems = dirty_size(localBot, _age.top());
153 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
154 if (dirty_n_elems == 0) return false;
155 localBot = decrement_index(localBot);
156 _bottom = localBot;
157 // This is necessary to prevent any read below from being reordered
158 // before the store just above.
159 OrderAccess::fence();
160 // g++ complains if the volatile result of the assignment is
161 // unused, so we cast the volatile away. We cannot cast directly
162 // to void, because gcc treats that as not using the result of the
163 // assignment. However, casting to E& means that we trigger an
164 // unused-value warning. So, we cast the E& to void.
165 (void) const_cast<E&>(t = _elems[localBot]);
166 // This is a second read of "age"; the "size()" above is the first.
167 // If there's still at least one element in the queue, based on the
168 // "_bottom" and "age" we've read, then there can be no interference with
169 // a "pop_global" operation, and we're done.
170 idx_t tp = _age.top(); // XXX
171 if (size(localBot, tp) > 0) {
172 assert(dirty_size(localBot, tp) != N - 1, "sanity");
173 TASKQUEUE_STATS_ONLY(stats.record_pop());
174 return true;
175 } else {
176 // Otherwise, the queue contained exactly one element; we take the slow
177 // path.
178 return pop_local_slow(localBot, _age.get());
179 }
180 }
181
182 template <class E, MEMFLAGS F, unsigned int N>
183 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
184 {
185 if (overflow_empty()) return false;
186 t = overflow_stack()->pop();
187 return true;
188 }
189
190 template<class E, MEMFLAGS F, unsigned int N>
191 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
192 Age oldAge = _age.get();
193 // Architectures with weak memory model require a barrier here
194 // to guarantee that bottom is not older than age,
195 // which is crucial for the correctness of the algorithm.
196 #if !(defined SPARC || defined IA32 || defined AMD64)
197 OrderAccess::fence();
198 #endif
199 uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
200 uint n_elems = size(localBot, oldAge.top());
201 if (n_elems == 0) {
202 return false;
203 }
204
205 // g++ complains if the volatile result of the assignment is
206 // unused, so we cast the volatile away. We cannot cast directly
207 // to void, because gcc treats that as not using the result of the
208 // assignment. However, casting to E& means that we trigger an
209 // unused-value warning. So, we cast the E& to void.
210 (void) const_cast<E&>(t = _elems[oldAge.top()]);
211 Age newAge(oldAge);
212 newAge.increment();
213 Age resAge = _age.cmpxchg(newAge, oldAge);
214
215 // Note that using "_bottom" here might fail, since a pop_local might
216 // have decremented it.
217 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
218 return resAge == oldAge;
219 }
220
221 template<class T, MEMFLAGS F> bool
222 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
223 if (_n > 2) {
224 uint k1 = queue_num;
225 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
226 uint k2 = queue_num;
227 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
228 // Sample both and try the larger.
229 uint sz1 = _queues[k1]->size();
230 uint sz2 = _queues[k2]->size();
231 if (sz2 > sz1) return _queues[k2]->pop_global(t);
232 else return _queues[k1]->pop_global(t);
233 } else if (_n == 2) {
234 // Just try the other one.
235 uint k = (queue_num + 1) % 2;
236 return _queues[k]->pop_global(t);
237 } else {
238 assert(_n == 1, "can't be zero.");
239 return false;
240 }
241 }
242
243 template<class T, MEMFLAGS F> bool
244 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
245 for (uint i = 0; i < 2 * _n; i++) {
246 if (steal_best_of_2(queue_num, seed, t)) {
247 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
248 return true;
249 }
250 }
251 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
252 return false;
253 }
254
255 template <unsigned int N, MEMFLAGS F>
256 inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile {
257 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
258 (volatile intptr_t *)&_data,
259 (intptr_t)old_age._data);
260 }
261
262 template<class E, MEMFLAGS F, unsigned int N>
263 template<class Fn>
264 inline void GenericTaskQueue<E, F, N>::iterate(Fn fn) {
265 uint iters = size();
266 uint index = _bottom;
267 for (uint i = 0; i < iters; ++i) {
268 index = decrement_index(index);
269 fn(const_cast<E&>(_elems[index])); // cast away volatility
270 }
271 }
272
273
274 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP