1 /*
2 * Copyright (c) 2016, Red Hat, Inc. and/or its affiliates.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
25 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
26
27 #include "memory/padded.hpp"
28 #include "utilities/taskqueue.hpp"
29 #include "runtime/mutex.hpp"
30
31 class Thread;
32
33 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
34 class BufferedOverflowTaskQueue: public OverflowTaskQueue<E, F, N>
35 {
36 public:
37 typedef OverflowTaskQueue<E, F, N> taskqueue_t;
38
39 BufferedOverflowTaskQueue() : _buf_empty(true) {};
40
41 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
42
43 // Push task t onto:
44 // - first, try buffer;
45 // - then, try the queue;
46 // - then, overflow stack.
47 // Return true.
48 inline bool push(E t);
49
50 // Attempt to pop from the buffer; return true if anything was popped.
51 inline bool pop_buffer(E &t);
52
53 inline void clear_buffer() { _buf_empty = true; }
54 inline bool buffer_empty() const { return _buf_empty; }
55 inline bool is_empty() const {
56 return taskqueue_t::is_empty() && buffer_empty();
57 }
58
59 private:
60 bool _buf_empty;
61 E _elem;
62 };
63
64 #ifdef _MSC_VER
65 #pragma warning(push)
66 // warning C4522: multiple assignment operators specified
67 #pragma warning(disable:4522)
68 #endif
69
70 // ObjArrayChunkedTask
71 //
72 // Encodes both regular oops, and the array oops plus chunking data for parallel array processing.
73 // The design goal is to make the regular oop ops very fast, because that would be the prevailing
74 // case. On the other hand, it should not block parallel array processing from efficiently dividing
75 // the array work.
76 //
77 // The idea is to steal the bits from the 64-bit oop to encode array data, if needed. For the
78 // proper divide-and-conquer strategies, we want to encode the "blocking" data. It turns out, the
79 // most efficient way to do this is to encode the array block as (chunk * 2^pow), where it is assumed
80 // that the block has the size of 2^pow. This requires for pow to have only 5 bits (2^32) to encode
81 // all possible arrays.
82 //
83 // |---------oop---------|-pow-|--chunk---|
84 // 0 49 54 64
85 //
86 // By definition, chunk == 0 means "no chunk", i.e. chunking starts from 1.
87 //
88 // This encoding gives a few interesting benefits:
89 //
90 // a) Encoding/decoding regular oops is very simple, because the upper bits are zero in that task:
91 //
92 // |---------oop---------|00000|0000000000| // no chunk data
93 //
94 // This helps the most ubiquitous path. The initialization amounts to putting the oop into the word
95 // with zero padding. Testing for "chunkedness" is testing for zero with chunk mask.
96 //
97 // b) Splitting tasks for divide-and-conquer is possible. Suppose we have chunk <C, P> that covers
98 // interval [ (C-1)*2^P; C*2^P ). We can then split it into two chunks:
99 // <2*C - 1, P-1>, that covers interval [ (2*C - 2)*2^(P-1); (2*C - 1)*2^(P-1) )
100 // <2*C, P-1>, that covers interval [ (2*C - 1)*2^(P-1); 2*C*2^(P-1) )
101 //
102 // Observe that the union of these two intervals is:
103 // [ (2*C - 2)*2^(P-1); 2*C*2^(P-1) )
104 //
105 // ...which is the original interval:
106 // [ (C-1)*2^P; C*2^P )
107 //
108 // c) The divide-and-conquer strategy could even start with chunk <1, round-log2-len(arr)>, and split
109 // down in the parallel threads, which alleviates the upfront (serial) splitting costs.
110 //
111 // Encoding limitations caused by current bitscales mean:
112 // 10 bits for chunk: max 1024 blocks per array
113 // 5 bits for power: max 2^32 array
114 // 49 bits for oop: max 512 TB of addressable space
115 //
116 // Stealing bits from oop trims down the addressable space. Stealing too few bits for chunk ID limits
117 // potential parallelism. Stealing too few bits for pow limits the maximum array size that can be handled.
118 // In future, these might be rebalanced to favor one degree of freedom against another. For example,
119 // if/when Arrays 2.0 bring 2^64-sized arrays, we might need to steal another bit for power. We could regain
120 // some bits back if chunks are counted in ObjArrayMarkingStride units.
121 //
122 // There is also a fallback version that uses plain fields, when we don't have enough space to steal the
123 // bits from the native pointer. It is useful to debug the _LP64 version.
124 //
125 #ifdef _LP64
126 class ObjArrayChunkedTask
127 {
128 public:
129 enum {
130 chunk_bits = 10,
131 pow_bits = 5,
132 oop_bits = sizeof(uintptr_t)*8 - chunk_bits - pow_bits,
133 };
134 enum {
135 oop_shift = 0,
136 pow_shift = oop_shift + oop_bits,
137 chunk_shift = pow_shift + pow_bits,
138 };
139
140 public:
141 ObjArrayChunkedTask(oop o = NULL) {
142 _obj = ((uintptr_t)(void*) o) << oop_shift;
143 }
144 ObjArrayChunkedTask(oop o, int chunk, int mult) {
145 assert(0 <= chunk && chunk < nth_bit(chunk_bits), err_msg("chunk is sane: %d", chunk));
146 assert(0 <= mult && mult < nth_bit(pow_bits), err_msg("pow is sane: %d", mult));
147 uintptr_t t_b = ((uintptr_t) chunk) << chunk_shift;
148 uintptr_t t_m = ((uintptr_t) mult) << pow_shift;
149 uintptr_t obj = (uintptr_t)(void*)o;
150 assert(obj < nth_bit(oop_bits), err_msg("obj ref is sane: " PTR_FORMAT, obj));
151 intptr_t t_o = obj << oop_shift;
152 _obj = t_o | t_m | t_b;
153 }
154 ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj) { }
155
156 ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {
157 _obj = t._obj;
158 return *this;
159 }
160 volatile ObjArrayChunkedTask&
161 operator =(const volatile ObjArrayChunkedTask& t) volatile {
162 (void)const_cast<uintptr_t&>(_obj = t._obj);
163 return *this;
164 }
165
166 inline oop obj() const { return (oop) reinterpret_cast<void*>((_obj >> oop_shift) & right_n_bits(oop_bits)); }
167 inline int chunk() const { return (int) (_obj >> chunk_shift) & right_n_bits(chunk_bits); }
168 inline int pow() const { return (int) ((_obj >> pow_shift) & right_n_bits(pow_bits)); }
169 inline bool is_not_chunked() const { return (_obj & ~right_n_bits(oop_bits + pow_bits)) == 0; }
170
171 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
172
173 static size_t max_addressable() {
174 return nth_bit(oop_bits);
175 }
176
177 static int chunk_size() {
178 return nth_bit(chunk_bits);
179 }
180
181 private:
182 uintptr_t _obj;
183 };
184 #else
185 class ObjArrayChunkedTask
186 {
187 public:
188 enum {
189 chunk_bits = 10,
190 pow_bits = 5,
191 };
192 public:
193 ObjArrayChunkedTask(oop o = NULL, int chunk = 0, int pow = 0): _obj(o) {
194 assert(0 <= chunk && chunk < nth_bit(chunk_bits), err_msg("chunk is sane: %d", chunk));
195 assert(0 <= pow && pow < nth_bit(pow_bits), err_msg("pow is sane: %d", pow));
196 _chunk = chunk;
197 _pow = pow;
198 }
199 ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj), _chunk(t._chunk), _pow(t._pow) { }
200
201 ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {
202 _obj = t._obj;
203 _chunk = t._chunk;
204 _pow = t._pow;
205 return *this;
206 }
207 volatile ObjArrayChunkedTask&
208 operator =(const volatile ObjArrayChunkedTask& t) volatile {
209 (void)const_cast<oop&>(_obj = t._obj);
210 _chunk = t._chunk;
211 _pow = t._pow;
212 return *this;
213 }
214
215 inline oop obj() const { return _obj; }
216 inline int chunk() const { return _chunk; }
217 inline int pow() const { return _pow; }
218
219 inline bool is_not_chunked() const { return _chunk == 0; }
220
221 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
222
223 static size_t max_addressable() {
224 return sizeof(oop);
225 }
226
227 static int chunk_size() {
228 return nth_bit(chunk_bits);
229 }
230
231 private:
232 oop _obj;
233 int _chunk;
234 int _pow;
235 };
236 #endif
237
238 typedef ObjArrayChunkedTask ShenandoahMarkTask;
239 typedef BufferedOverflowTaskQueue<ShenandoahMarkTask, mtGC> ShenandoahBufferedOverflowTaskQueue;
240 typedef Padded<ShenandoahBufferedOverflowTaskQueue> ShenandoahObjToScanQueue;
241
242 template <class T, MEMFLAGS F>
243 class ParallelClaimableQueueSet: public GenericTaskQueueSet<T, F> {
244 private:
245 volatile jint _claimed_index;
246 debug_only(uint _reserved; )
247
248 public:
249 using GenericTaskQueueSet<T, F>::size;
250
251 public:
252 ParallelClaimableQueueSet(int n) : GenericTaskQueueSet<T, F>(n), _claimed_index(0) {
253 debug_only(_reserved = 0; )
254 }
255
256 void clear_claimed() { _claimed_index = 0; }
257 T* claim_next();
258
259 // reserve queues that not for parallel claiming
260 void reserve(uint n) {
261 assert(n <= size(), "Sanity");
262 _claimed_index = (jint)n;
263 debug_only(_reserved = n;)
264 }
265
266 debug_only(uint get_reserved() const { return (uint)_reserved; })
267 };
268
269
270 template <class T, MEMFLAGS F>
271 T* ParallelClaimableQueueSet<T, F>::claim_next() {
272 jint size = (jint)GenericTaskQueueSet<T, F>::size();
273
274 if (_claimed_index >= size) {
275 return NULL;
276 }
277
278 jint index = Atomic::add(1, &_claimed_index);
279
280 if (index <= size) {
281 return GenericTaskQueueSet<T, F>::queue((uint)index - 1);
282 } else {
283 return NULL;
284 }
285 }
286
287 class ShenandoahObjToScanQueueSet: public ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC> {
288
289 public:
290 ShenandoahObjToScanQueueSet(int n) : ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC>(n) {
291 }
292
293 bool is_empty();
294 void clear();
295
296 #if TASKQUEUE_STATS
297 static void print_taskqueue_stats_hdr(outputStream* const st);
298 void print_taskqueue_stats();
299 void reset_taskqueue_stats();
300 #endif // TASKQUEUE_STATS
301 };
302
303
304 /*
305 * This is an enhanced implementation of Google's work stealing
306 * protocol, which is described in the paper:
307 * Understanding and improving JVM GC work stealing at the data center scale
308 * (http://dl.acm.org/citation.cfm?id=2926706)
309 *
310 * Instead of a dedicated spin-master, our implementation will let spin-master to relinquish
311 * the role before it goes to sleep/wait, so allows newly arrived thread to compete for the role.
312 * The intention of above enhancement, is to reduce spin-master's latency on detecting new tasks
313 * for stealing and termination condition.
314 */
315
316 class ShenandoahTaskTerminator: public ParallelTaskTerminator {
317 private:
318 Monitor* _blocker;
319 Thread* _spin_master;
320
321
322 public:
323 ShenandoahTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :
324 ParallelTaskTerminator(n_threads, queue_set), _spin_master(NULL) {
325 _blocker = new Monitor(Mutex::leaf, "ShenandoahTaskTerminator", false);
326 }
327
328 ~ShenandoahTaskTerminator() {
329 assert(_blocker != NULL, "Can not be NULL");
330 delete _blocker;
331 }
332
333 bool offer_termination(TerminatorTerminator* terminator);
334
335 private:
336 size_t tasks_in_queue_set() { return _queue_set->tasks(); }
337
338
339 /*
340 * Perform spin-master task.
341 * return true if termination condition is detected
342 * otherwise, return false
343 */
344 bool do_spin_master_work(TerminatorTerminator* terminator);
345 };
346
347 class ShenandoahCancelledTerminatorTerminator : public TerminatorTerminator {
348 virtual bool should_exit_termination() {
349 return false;
350 }
351 virtual bool should_force_termination() {
352 return true;
353 }
354 };
355
356 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP