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
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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 = _array_allocator.allocate(N);
48 }
49
50 template<class E, MEMFLAGS F, unsigned int N>
51 inline GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
52 FREE_C_HEAP_ARRAY(E, _elems);
53 }
54
55 template<class E, MEMFLAGS F, unsigned int N>
56 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
57 if (dirty_n_elems == N - 1) {
58 // Actually means 0, so do the push.
59 uint localBot = _bottom;
60 // g++ complains if the volatile result of the assignment is
61 // unused, so we cast the volatile away. We cannot cast directly
62 // to void, because gcc treats that as not using the result of the
63 // assignment. However, casting to E& means that we trigger an
64 // unused-value warning. So, we cast the E& to void.
65 (void)const_cast<E&>(_elems[localBot] = t);
66 OrderAccess::release_store(&_bottom, increment_index(localBot));
67 TASKQUEUE_STATS_ONLY(stats.record_push());
68 return true;
69 }
70 return false;
71 }
72
73 template<class E, MEMFLAGS F, unsigned int N> inline bool
74 GenericTaskQueue<E, F, N>::push(E t) {
75 uint localBot = _bottom;
76 assert(localBot < N, "_bottom out of range.");
77 idx_t top = _age.top();
78 uint dirty_n_elems = dirty_size(localBot, top);
79 assert(dirty_n_elems < N, "n_elems out of range.");
80 if (dirty_n_elems < max_elems()) {
81 // g++ complains if the volatile result of the assignment is
82 // unused, so we cast the volatile away. We cannot cast directly
83 // to void, because gcc treats that as not using the result of the
84 // assignment. However, casting to E& means that we trigger an
85 // unused-value warning. So, we cast the E& to void.
86 (void) const_cast<E&>(_elems[localBot] = t);
87 OrderAccess::release_store(&_bottom, increment_index(localBot));
88 TASKQUEUE_STATS_ONLY(stats.record_push());
89 return true;
90 } else {
91 return push_slow(t, dirty_n_elems);
92 }
93 }
94
95 template <class E, MEMFLAGS F, unsigned int N>
96 inline bool OverflowTaskQueue<E, F, N>::push(E t)
97 {
98 if (!taskqueue_t::push(t)) {
99 overflow_stack()->push(t);
100 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
101 }
102 return true;
103 }
104
105 // pop_local_slow() is done by the owning thread and is trying to
106 // get the last task in the queue. It will compete with pop_global()
107 // that will be used by other threads. The tag age is incremented
108 // whenever the queue goes empty which it will do here if this thread
109 // gets the last task or in pop_global() if the queue wraps (top == 0
110 // and pop_global() succeeds, see pop_global()).
111 template<class E, MEMFLAGS F, unsigned int N>
112 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
113 // This queue was observed to contain exactly one element; either this
114 // thread will claim it, or a competing "pop_global". In either case,
115 // the queue will be logically empty afterwards. Create a new Age value
116 // that represents the empty queue for the given value of "_bottom". (We
117 // must also increment "tag" because of the case where "bottom == 1",
118 // "top == 0". A pop_global could read the queue element in that case,
119 // then have the owner thread do a pop followed by another push. Without
120 // the incrementing of "tag", the pop_global's CAS could succeed,
121 // allowing it to believe it has claimed the stale element.)
122 Age newAge((idx_t)localBot, oldAge.tag() + 1);
123 // Perhaps a competing pop_global has already incremented "top", in which
124 // case it wins the element.
125 if (localBot == oldAge.top()) {
126 // No competing pop_global has yet incremented "top"; we'll try to
127 // install new_age, thus claiming the element.
128 Age tempAge = _age.cmpxchg(newAge, oldAge);
129 if (tempAge == oldAge) {
130 // We win.
131 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
132 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
133 return true;
134 }
135 }
136 // We lose; a completing pop_global gets the element. But the queue is empty
137 // and top is greater than bottom. Fix this representation of the empty queue
138 // to become the canonical one.
139 _age.set(newAge);
140 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
141 return false;
142 }
143
144 template<class E, MEMFLAGS F, unsigned int N> inline bool
145 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
146 uint localBot = _bottom;
147 // This value cannot be N-1. That can only occur as a result of
148 // the assignment to bottom in this method. If it does, this method
149 // resets the size to 0 before the next call (which is sequential,
150 // since this is pop_local.)
151 uint dirty_n_elems = dirty_size(localBot, _age.top());
152 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
153 if (dirty_n_elems == 0) return false;
154 localBot = decrement_index(localBot);
155 _bottom = localBot;
156 // This is necessary to prevent any read below from being reordered
157 // before the store just above.
158 OrderAccess::fence();
159 // g++ complains if the volatile result of the assignment is
160 // unused, so we cast the volatile away. We cannot cast directly
161 // to void, because gcc treats that as not using the result of the
162 // assignment. However, casting to E& means that we trigger an
163 // unused-value warning. So, we cast the E& to void.
164 (void) const_cast<E&>(t = _elems[localBot]);
165 // This is a second read of "age"; the "size()" above is the first.
166 // If there's still at least one element in the queue, based on the
167 // "_bottom" and "age" we've read, then there can be no interference with
168 // a "pop_global" operation, and we're done.
169 idx_t tp = _age.top(); // XXX
170 if (size(localBot, tp) > 0) {
171 assert(dirty_size(localBot, tp) != N - 1, "sanity");
172 TASKQUEUE_STATS_ONLY(stats.record_pop());
173 return true;
174 } else {
175 // Otherwise, the queue contained exactly one element; we take the slow
176 // path.
177 return pop_local_slow(localBot, _age.get());
178 }
179 }
180
181 template <class E, MEMFLAGS F, unsigned int N>
182 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
183 {
184 if (overflow_empty()) return false;
185 t = overflow_stack()->pop();
186 return true;
187 }
188
189 template<class E, MEMFLAGS F, unsigned int N>
190 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
191 Age oldAge = _age.get();
192 // Architectures with weak memory model require a barrier here
193 // to guarantee that bottom is not older than age,
194 // which is crucial for the correctness of the algorithm.
195 #if !(defined SPARC || defined IA32 || defined AMD64)
196 OrderAccess::fence();
197 #endif
198 uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
199 uint n_elems = size(localBot, oldAge.top());
200 if (n_elems == 0) {
201 return false;
202 }
203
204 // g++ complains if the volatile result of the assignment is
205 // unused, so we cast the volatile away. We cannot cast directly
206 // to void, because gcc treats that as not using the result of the
207 // assignment. However, casting to E& means that we trigger an
208 // unused-value warning. So, we cast the E& to void.
209 (void) const_cast<E&>(t = _elems[oldAge.top()]);
210 Age newAge(oldAge);
211 newAge.increment();
212 Age resAge = _age.cmpxchg(newAge, oldAge);
213
214 // Note that using "_bottom" here might fail, since a pop_local might
215 // have decremented it.
216 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
217 return resAge == oldAge;
218 }
219
220 template<class T, MEMFLAGS F> bool
221 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
222 if (_n > 2) {
223 uint k1 = queue_num;
224 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
225 uint k2 = queue_num;
226 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
227 // Sample both and try the larger.
228 uint sz1 = _queues[k1]->size();
229 uint sz2 = _queues[k2]->size();
230 if (sz2 > sz1) return _queues[k2]->pop_global(t);
231 else return _queues[k1]->pop_global(t);
232 } else if (_n == 2) {
233 // Just try the other one.
234 uint k = (queue_num + 1) % 2;
235 return _queues[k]->pop_global(t);
236 } else {
237 assert(_n == 1, "can't be zero.");
238 return false;
239 }
240 }
241
242 template<class T, MEMFLAGS F> bool
243 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
244 for (uint i = 0; i < 2 * _n; i++) {
245 if (steal_best_of_2(queue_num, seed, t)) {
246 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
247 return true;
248 }
249 }
250 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
251 return false;
252 }
253
254 template <unsigned int N, MEMFLAGS F>
255 inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile {
256 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
257 (volatile intptr_t *)&_data,
258 (intptr_t)old_age._data);
259 }
260
261 template<class E, MEMFLAGS F, unsigned int N>
262 inline void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {
263 // tty->print_cr("START OopTaskQueue::oops_do");
264 uint iters = size();
265 uint index = _bottom;
266 for (uint i = 0; i < iters; ++i) {
267 index = decrement_index(index);
268 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
269 // index, &_elems[index], _elems[index]);
270 E* t = (E*)&_elems[index]; // cast away volatility
271 oop* p = (oop*)t;
272 assert((*t)->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(*t)));
273 f->do_oop(p);
274 }
275 // tty->print_cr("END OopTaskQueue::oops_do");
276 }
277
278
279 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP