1 /*
2 * Copyright (c) 2016, 2020, Red Hat, Inc. 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_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
27
28 #include "gc/shared/taskTerminator.hpp"
29 #include "gc/shared/taskqueue.hpp"
30 #include "gc/shenandoah/shenandoahPadding.hpp"
31 #include "memory/allocation.hpp"
32 #include "runtime/atomic.hpp"
33 #include "runtime/mutex.hpp"
34 #include "runtime/thread.hpp"
35
36 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
37 class BufferedOverflowTaskQueue: public OverflowTaskQueue<E, F, N>
38 {
39 public:
40 typedef OverflowTaskQueue<E, F, N> taskqueue_t;
41
42 BufferedOverflowTaskQueue() : _buf_empty(true) {};
43
44 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
45
46 // Push task t into the queue. Returns true on success.
47 inline bool push(E t);
48
49 // Attempt to pop from the queue. Returns true on success.
50 inline bool pop(E &t);
51
52 inline void clear();
53
54 inline bool is_empty() const {
55 return _buf_empty && taskqueue_t::is_empty();
56 }
57
58 private:
59 bool _buf_empty;
60 E _elem;
61 };
62
63 // ObjArrayChunkedTask
64 //
65 // Encodes both regular oops, and the array oops plus chunking data for parallel array processing.
66 // The design goal is to make the regular oop ops very fast, because that would be the prevailing
67 // case. On the other hand, it should not block parallel array processing from efficiently dividing
68 // the array work.
69 //
70 // The idea is to steal the bits from the 64-bit oop to encode array data, if needed. For the
71 // proper divide-and-conquer strategies, we want to encode the "blocking" data. It turns out, the
72 // most efficient way to do this is to encode the array block as (chunk * 2^pow), where it is assumed
73 // that the block has the size of 2^pow. This requires for pow to have only 5 bits (2^32) to encode
74 // all possible arrays.
75 //
76 // |---------oop---------|-pow-|--chunk---|
77 // 0 49 54 64
78 //
79 // By definition, chunk == 0 means "no chunk", i.e. chunking starts from 1.
80 //
81 // This encoding gives a few interesting benefits:
82 //
83 // a) Encoding/decoding regular oops is very simple, because the upper bits are zero in that task:
84 //
85 // |---------oop---------|00000|0000000000| // no chunk data
86 //
87 // This helps the most ubiquitous path. The initialization amounts to putting the oop into the word
88 // with zero padding. Testing for "chunkedness" is testing for zero with chunk mask.
89 //
90 // b) Splitting tasks for divide-and-conquer is possible. Suppose we have chunk <C, P> that covers
91 // interval [ (C-1)*2^P; C*2^P ). We can then split it into two chunks:
92 // <2*C - 1, P-1>, that covers interval [ (2*C - 2)*2^(P-1); (2*C - 1)*2^(P-1) )
93 // <2*C, P-1>, that covers interval [ (2*C - 1)*2^(P-1); 2*C*2^(P-1) )
94 //
95 // Observe that the union of these two intervals is:
96 // [ (2*C - 2)*2^(P-1); 2*C*2^(P-1) )
97 //
98 // ...which is the original interval:
99 // [ (C-1)*2^P; C*2^P )
100 //
101 // c) The divide-and-conquer strategy could even start with chunk <1, round-log2-len(arr)>, and split
102 // down in the parallel threads, which alleviates the upfront (serial) splitting costs.
103 //
104 // Encoding limitations caused by current bitscales mean:
105 // 10 bits for chunk: max 1024 blocks per array
106 // 5 bits for power: max 2^32 array
107 // 49 bits for oop: max 512 TB of addressable space
108 //
109 // Stealing bits from oop trims down the addressable space. Stealing too few bits for chunk ID limits
110 // potential parallelism. Stealing too few bits for pow limits the maximum array size that can be handled.
111 // In future, these might be rebalanced to favor one degree of freedom against another. For example,
112 // if/when Arrays 2.0 bring 2^64-sized arrays, we might need to steal another bit for power. We could regain
113 // some bits back if chunks are counted in ObjArrayMarkingStride units.
114 //
115 // There is also a fallback version that uses plain fields, when we don't have enough space to steal the
116 // bits from the native pointer. It is useful to debug the optimized version.
117 //
118
119 #ifdef _MSC_VER
120 #pragma warning(push)
121 // warning C4522: multiple assignment operators specified
122 #pragma warning( disable:4522 )
123 #endif
124
125 #ifdef _LP64
126 #define SHENANDOAH_OPTIMIZED_OBJTASK 1
127 #else
128 #define SHENANDOAH_OPTIMIZED_OBJTASK 0
129 #endif
130
131 #if SHENANDOAH_OPTIMIZED_OBJTASK
132 class ObjArrayChunkedTask
133 {
134 public:
135 enum {
136 chunk_bits = 10,
137 pow_bits = 5,
138 oop_bits = sizeof(uintptr_t)*8 - chunk_bits - pow_bits
139 };
140 enum {
141 oop_shift = 0,
142 pow_shift = oop_shift + oop_bits,
143 chunk_shift = pow_shift + pow_bits
144 };
145
146 public:
147 ObjArrayChunkedTask(oop o = NULL) {
148 assert(decode_oop(encode_oop(o)) == o, "oop can be encoded: " PTR_FORMAT, p2i(o));
149 _obj = encode_oop(o);
150 }
151 ObjArrayChunkedTask(oop o, int chunk, int pow) {
152 assert(decode_oop(encode_oop(o)) == o, "oop can be encoded: " PTR_FORMAT, p2i(o));
153 assert(decode_chunk(encode_chunk(chunk)) == chunk, "chunk can be encoded: %d", chunk);
154 assert(decode_pow(encode_pow(pow)) == pow, "pow can be encoded: %d", pow);
155 _obj = encode_oop(o) | encode_chunk(chunk) | encode_pow(pow);
156 }
157
158 // Trivially copyable.
159
160 inline oop decode_oop(uintptr_t val) const {
161 return (oop) reinterpret_cast<void*>((val >> oop_shift) & right_n_bits(oop_bits));
162 }
163
164 inline int decode_chunk(uintptr_t val) const {
165 return (int) ((val >> chunk_shift) & right_n_bits(chunk_bits));
166 }
167
168 inline int decode_pow(uintptr_t val) const {
169 return (int) ((val >> pow_shift) & right_n_bits(pow_bits));
170 }
171
172 inline uintptr_t encode_oop(oop obj) const {
173 return ((uintptr_t)(void*) obj) << oop_shift;
174 }
175
176 inline uintptr_t encode_chunk(int chunk) const {
177 return ((uintptr_t) chunk) << chunk_shift;
178 }
179
180 inline uintptr_t encode_pow(int pow) const {
181 return ((uintptr_t) pow) << pow_shift;
182 }
183
184 inline oop obj() const { return decode_oop(_obj); }
185 inline int chunk() const { return decode_chunk(_obj); }
186 inline int pow() const { return decode_pow(_obj); }
187 inline bool is_not_chunked() const { return (_obj & ~right_n_bits(oop_bits + pow_bits)) == 0; }
188
189 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
190
191 static uintptr_t max_addressable() {
192 return nth_bit(oop_bits);
193 }
194
195 static int chunk_size() {
196 return nth_bit(chunk_bits);
197 }
198
199 private:
200 uintptr_t _obj;
201 };
202 #else
203 class ObjArrayChunkedTask
204 {
205 public:
206 enum {
207 chunk_bits = 10,
208 pow_bits = 5,
209 };
210 public:
211 ObjArrayChunkedTask(oop o = NULL, int chunk = 0, int pow = 0): _obj(o) {
212 assert(0 <= chunk && chunk < nth_bit(chunk_bits), "chunk is sane: %d", chunk);
213 assert(0 <= pow && pow < nth_bit(pow_bits), "pow is sane: %d", pow);
214 _chunk = chunk;
215 _pow = pow;
216 }
217
218 // Trivially copyable.
219
220 inline oop obj() const { return _obj; }
221 inline int chunk() const { return _chunk; }
222 inline int pow() const { return _pow; }
223
224 inline bool is_not_chunked() const { return _chunk == 0; }
225
226 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
227
228 static size_t max_addressable() {
229 return sizeof(oop);
230 }
231
232 static int chunk_size() {
233 return nth_bit(chunk_bits);
234 }
235
236 private:
237 oop _obj;
238 int _chunk;
239 int _pow;
240 };
241 #endif // SHENANDOAH_OPTIMIZED_OBJTASK
242
243 #ifdef _MSC_VER
244 #pragma warning(pop)
245 #endif
246
247 typedef ObjArrayChunkedTask ShenandoahMarkTask;
248 typedef BufferedOverflowTaskQueue<ShenandoahMarkTask, mtGC> ShenandoahBufferedOverflowTaskQueue;
249 typedef Padded<ShenandoahBufferedOverflowTaskQueue> ShenandoahObjToScanQueue;
250
251 template <class T, MEMFLAGS F>
252 class ParallelClaimableQueueSet: public GenericTaskQueueSet<T, F> {
253 private:
254 shenandoah_padding(0);
255 volatile jint _claimed_index;
256 shenandoah_padding(1);
257
258 debug_only(uint _reserved; )
259
260 public:
261 using GenericTaskQueueSet<T, F>::size;
262
263 public:
264 ParallelClaimableQueueSet(int n) : GenericTaskQueueSet<T, F>(n), _claimed_index(0) {
265 debug_only(_reserved = 0; )
266 }
267
268 void clear_claimed() { _claimed_index = 0; }
269 T* claim_next();
270
271 // reserve queues that not for parallel claiming
272 void reserve(uint n) {
273 assert(n <= size(), "Sanity");
274 _claimed_index = (jint)n;
275 debug_only(_reserved = n;)
276 }
277
278 debug_only(uint get_reserved() const { return (uint)_reserved; })
279 };
280
281 template <class T, MEMFLAGS F>
282 T* ParallelClaimableQueueSet<T, F>::claim_next() {
283 jint size = (jint)GenericTaskQueueSet<T, F>::size();
284
285 if (_claimed_index >= size) {
286 return NULL;
287 }
288
289 jint index = Atomic::add(&_claimed_index, 1);
290
291 if (index <= size) {
292 return GenericTaskQueueSet<T, F>::queue((uint)index - 1);
293 } else {
294 return NULL;
295 }
296 }
297
298 class ShenandoahObjToScanQueueSet: public ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC> {
299 public:
300 ShenandoahObjToScanQueueSet(int n) : ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC>(n) {}
301
302 bool is_empty();
303 void clear();
304
305 #if TASKQUEUE_STATS
306 static void print_taskqueue_stats_hdr(outputStream* const st);
307 void print_taskqueue_stats() const;
308 void reset_taskqueue_stats();
309 #endif // TASKQUEUE_STATS
310 };
311
312 class ShenandoahTerminatorTerminator : public TerminatorTerminator {
313 private:
314 ShenandoahHeap* _heap;
315 public:
316 ShenandoahTerminatorTerminator(ShenandoahHeap* const heap) : _heap(heap) { }
317 virtual bool should_exit_termination();
318 };
319
320 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP