1 /* 2 * Copyright (c) 2001, 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. 22 * 23 */ 24 25 #ifndef SHARE_VM_UTILITIES_TASKQUEUE_HPP 26 #define SHARE_VM_UTILITIES_TASKQUEUE_HPP 27 28 #include "memory/allocation.hpp" 29 #include "utilities/stack.hpp" 30 31 // Simple TaskQueue stats that are collected by default in debug builds. 32 33 #if !defined(TASKQUEUE_STATS) && defined(ASSERT) 34 #define TASKQUEUE_STATS 1 35 #elif !defined(TASKQUEUE_STATS) 36 #define TASKQUEUE_STATS 0 37 #endif 38 39 #if TASKQUEUE_STATS 40 #define TASKQUEUE_STATS_ONLY(code) code 41 #else 42 #define TASKQUEUE_STATS_ONLY(code) 43 #endif // TASKQUEUE_STATS 44 45 #if TASKQUEUE_STATS 46 class TaskQueueStats { 47 public: 48 enum StatId { 49 push, // number of taskqueue pushes 50 pop, // number of taskqueue pops 51 pop_slow, // subset of taskqueue pops that were done slow-path 52 steal_attempt, // number of taskqueue steal attempts 53 steal, // number of taskqueue steals 54 overflow, // number of overflow pushes 55 overflow_max_len, // max length of overflow stack 56 last_stat_id 57 }; 58 59 public: 60 inline TaskQueueStats() { reset(); } 61 62 inline void record_push() { ++_stats[push]; } 63 inline void record_pop() { ++_stats[pop]; } 64 inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; } 65 inline void record_steal(bool success); 66 inline void record_overflow(size_t new_length); 67 68 TaskQueueStats & operator +=(const TaskQueueStats & addend); 69 70 inline size_t get(StatId id) const { return _stats[id]; } 71 inline const size_t* get() const { return _stats; } 72 73 inline void reset(); 74 75 // Print the specified line of the header (does not include a line separator). 76 static void print_header(unsigned int line, outputStream* const stream = tty, 77 unsigned int width = 10); 78 // Print the statistics (does not include a line separator). 79 void print(outputStream* const stream = tty, unsigned int width = 10) const; 80 81 DEBUG_ONLY(void verify() const;) 82 83 private: 84 size_t _stats[last_stat_id]; 85 static const char * const _names[last_stat_id]; 86 }; 87 88 void TaskQueueStats::record_steal(bool success) { 89 ++_stats[steal_attempt]; 90 if (success) ++_stats[steal]; 91 } 92 93 void TaskQueueStats::record_overflow(size_t new_len) { 94 ++_stats[overflow]; 95 if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len; 96 } 97 98 void TaskQueueStats::reset() { 99 memset(_stats, 0, sizeof(_stats)); 100 } 101 #endif // TASKQUEUE_STATS 102 103 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances. 104 105 template <unsigned int N, MEMFLAGS F> 106 class TaskQueueSuper: public CHeapObj<F> { 107 protected: 108 // Internal type for indexing the queue; also used for the tag. 109 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t; 110 111 // The first free element after the last one pushed (mod N). 112 volatile uint _bottom; 113 114 enum { MOD_N_MASK = N - 1 }; 115 116 class Age { 117 public: 118 Age(size_t data = 0) { _data = data; } 119 Age(const Age& age) { _data = age._data; } 120 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; } 121 122 Age get() const volatile { return _data; } 123 void set(Age age) volatile { _data = age._data; } 124 125 idx_t top() const volatile { return _fields._top; } 126 idx_t tag() const volatile { return _fields._tag; } 127 128 // Increment top; if it wraps, increment tag also. 129 void increment() { 130 _fields._top = increment_index(_fields._top); 131 if (_fields._top == 0) ++_fields._tag; 132 } 133 134 Age cmpxchg(const Age new_age, const Age old_age) volatile; 135 136 bool operator ==(const Age& other) const { return _data == other._data; } 137 138 private: 139 struct fields { 140 idx_t _top; 141 idx_t _tag; 142 }; 143 union { 144 size_t _data; 145 fields _fields; 146 }; 147 }; 148 149 volatile Age _age; 150 151 // These both operate mod N. 152 static uint increment_index(uint ind) { 153 return (ind + 1) & MOD_N_MASK; 154 } 155 static uint decrement_index(uint ind) { 156 return (ind - 1) & MOD_N_MASK; 157 } 158 159 // Returns a number in the range [0..N). If the result is "N-1", it should be 160 // interpreted as 0. 161 uint dirty_size(uint bot, uint top) const { 162 return (bot - top) & MOD_N_MASK; 163 } 164 165 // Returns the size corresponding to the given "bot" and "top". 166 uint size(uint bot, uint top) const { 167 uint sz = dirty_size(bot, top); 168 // Has the queue "wrapped", so that bottom is less than top? There's a 169 // complicated special case here. A pair of threads could perform pop_local 170 // and pop_global operations concurrently, starting from a state in which 171 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom, 172 // and the pop_global in incrementing _top (in which case the pop_global 173 // will be awarded the contested queue element.) The resulting state must 174 // be interpreted as an empty queue. (We only need to worry about one such 175 // event: only the queue owner performs pop_local's, and several concurrent 176 // threads attempting to perform the pop_global will all perform the same 177 // CAS, and only one can succeed.) Any stealing thread that reads after 178 // either the increment or decrement will see an empty queue, and will not 179 // join the competitors. The "sz == -1 || sz == N-1" state will not be 180 // modified by concurrent queues, so the owner thread can reset the state to 181 // _bottom == top so subsequent pushes will be performed normally. 182 return (sz == N - 1) ? 0 : sz; 183 } 184 185 public: 186 TaskQueueSuper() : _bottom(0), _age() {} 187 188 // Return true if the TaskQueue contains/does not contain any tasks. 189 bool peek() const { return _bottom != _age.top(); } 190 bool is_empty() const { return size() == 0; } 191 192 // Return an estimate of the number of elements in the queue. 193 // The "careful" version admits the possibility of pop_local/pop_global 194 // races. 195 uint size() const { 196 return size(_bottom, _age.top()); 197 } 198 199 uint dirty_size() const { 200 return dirty_size(_bottom, _age.top()); 201 } 202 203 void set_empty() { 204 _bottom = 0; 205 _age.set(0); 206 } 207 208 // Maximum number of elements allowed in the queue. This is two less 209 // than the actual queue size, for somewhat complicated reasons. 210 uint max_elems() const { return N - 2; } 211 212 // Total size of queue. 213 static const uint total_size() { return N; } 214 215 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;) 216 }; 217 218 // 219 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double- 220 // ended-queue (deque), intended for use in work stealing. Queue operations 221 // are non-blocking. 222 // 223 // A queue owner thread performs push() and pop_local() operations on one end 224 // of the queue, while other threads may steal work using the pop_global() 225 // method. 226 // 227 // The main difference to the original algorithm is that this 228 // implementation allows wrap-around at the end of its allocated 229 // storage, which is an array. 230 // 231 // The original paper is: 232 // 233 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G. 234 // Thread scheduling for multiprogrammed multiprocessors. 235 // Theory of Computing Systems 34, 2 (2001), 115-144. 236 // 237 // The following paper provides an correctness proof and an 238 // implementation for weakly ordered memory models including (pseudo-) 239 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is 240 // similar to ABP, with the main difference that it allows resizing of the 241 // underlying storage: 242 // 243 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z. 244 // Correct and efficient work-stealing for weak memory models 245 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and 246 // practice of parallel programming (PPoPP 2013), 69-80 247 // 248 249 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE> 250 class GenericTaskQueue: public TaskQueueSuper<N, F> { 251 ArrayAllocator<E, F> _array_allocator; 252 protected: 253 typedef typename TaskQueueSuper<N, F>::Age Age; 254 typedef typename TaskQueueSuper<N, F>::idx_t idx_t; 255 256 using TaskQueueSuper<N, F>::_bottom; 257 using TaskQueueSuper<N, F>::_age; 258 using TaskQueueSuper<N, F>::increment_index; 259 using TaskQueueSuper<N, F>::decrement_index; 260 using TaskQueueSuper<N, F>::dirty_size; 261 262 public: 263 using TaskQueueSuper<N, F>::max_elems; 264 using TaskQueueSuper<N, F>::size; 265 266 #if TASKQUEUE_STATS 267 using TaskQueueSuper<N, F>::stats; 268 #endif 269 270 private: 271 // Slow paths for push, pop_local. (pop_global has no fast path.) 272 bool push_slow(E t, uint dirty_n_elems); 273 bool pop_local_slow(uint localBot, Age oldAge); 274 275 public: 276 typedef E element_type; 277 278 // Initializes the queue to empty. 279 GenericTaskQueue(); 280 281 void initialize(); 282 283 // Push the task "t" on the queue. Returns "false" iff the queue is full. 284 inline bool push(E t); 285 286 // Attempts to claim a task from the "local" end of the queue (the most 287 // recently pushed). If successful, returns true and sets t to the task; 288 // otherwise, returns false (the queue is empty). 289 inline bool pop_local(volatile E& t); 290 291 // Like pop_local(), but uses the "global" end of the queue (the least 292 // recently pushed). 293 bool pop_global(volatile E& t); 294 295 // Delete any resource associated with the queue. 296 ~GenericTaskQueue(); 297 298 // apply the closure to all elements in the task queue 299 void oops_do(OopClosure* f); 300 301 private: 302 // Element array. 303 volatile E* _elems; 304 }; 305 306 template<class E, MEMFLAGS F, unsigned int N> 307 GenericTaskQueue<E, F, N>::GenericTaskQueue() { 308 assert(sizeof(Age) == sizeof(size_t), "Depends on this."); 309 } 310 311 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for 312 // elements that do not fit in the TaskQueue. 313 // 314 // This class hides two methods from super classes: 315 // 316 // push() - push onto the task queue or, if that fails, onto the overflow stack 317 // is_empty() - return true if both the TaskQueue and overflow stack are empty 318 // 319 // Note that size() is not hidden--it returns the number of elements in the 320 // TaskQueue, and does not include the size of the overflow stack. This 321 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues. 322 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE> 323 class OverflowTaskQueue: public GenericTaskQueue<E, F, N> 324 { 325 public: 326 typedef Stack<E, F> overflow_t; 327 typedef GenericTaskQueue<E, F, N> taskqueue_t; 328 329 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;) 330 331 // Push task t onto the queue or onto the overflow stack. Return true. 332 inline bool push(E t); 333 334 // Attempt to pop from the overflow stack; return true if anything was popped. 335 inline bool pop_overflow(E& t); 336 337 inline overflow_t* overflow_stack() { return &_overflow_stack; } 338 339 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); } 340 inline bool overflow_empty() const { return _overflow_stack.is_empty(); } 341 inline bool is_empty() const { 342 return taskqueue_empty() && overflow_empty(); 343 } 344 345 private: 346 overflow_t _overflow_stack; 347 }; 348 349 class TaskQueueSetSuper { 350 protected: 351 static int randomParkAndMiller(int* seed0); 352 public: 353 // Returns "true" if some TaskQueue in the set contains a task. 354 virtual bool peek() = 0; 355 }; 356 357 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper { 358 }; 359 360 template<class T, MEMFLAGS F> 361 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> { 362 private: 363 uint _n; 364 T** _queues; 365 366 public: 367 typedef typename T::element_type E; 368 369 GenericTaskQueueSet(int n); 370 371 bool steal_best_of_2(uint queue_num, int* seed, E& t); 372 373 void register_queue(uint i, T* q); 374 375 T* queue(uint n); 376 377 // The thread with queue number "queue_num" (and whose random number seed is 378 // at "seed") is trying to steal a task from some other queue. (It may try 379 // several queues, according to some configuration parameter.) If some steal 380 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns 381 // false. 382 bool steal(uint queue_num, int* seed, E& t); 383 384 bool peek(); 385 }; 386 387 template<class T, MEMFLAGS F> void 388 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) { 389 assert(i < _n, "index out of range."); 390 _queues[i] = q; 391 } 392 393 template<class T, MEMFLAGS F> T* 394 GenericTaskQueueSet<T, F>::queue(uint i) { 395 return _queues[i]; 396 } 397 398 template<class T, MEMFLAGS F> 399 bool GenericTaskQueueSet<T, F>::peek() { 400 // Try all the queues. 401 for (uint j = 0; j < _n; j++) { 402 if (_queues[j]->peek()) 403 return true; 404 } 405 return false; 406 } 407 408 // When to terminate from the termination protocol. 409 class TerminatorTerminator: public CHeapObj<mtInternal> { 410 public: 411 virtual bool should_exit_termination() = 0; 412 }; 413 414 // A class to aid in the termination of a set of parallel tasks using 415 // TaskQueueSet's for work stealing. 416 417 #undef TRACESPINNING 418 419 class ParallelTaskTerminator: public StackObj { 420 private: 421 uint _n_threads; 422 TaskQueueSetSuper* _queue_set; 423 uint _offered_termination; 424 425 #ifdef TRACESPINNING 426 static uint _total_yields; 427 static uint _total_spins; 428 static uint _total_peeks; 429 #endif 430 431 bool peek_in_queue_set(); 432 protected: 433 virtual void yield(); 434 void sleep(uint millis); 435 436 public: 437 438 // "n_threads" is the number of threads to be terminated. "queue_set" is a 439 // queue sets of work queues of other threads. 440 ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set); 441 442 // The current thread has no work, and is ready to terminate if everyone 443 // else is. If returns "true", all threads are terminated. If returns 444 // "false", available work has been observed in one of the task queues, 445 // so the global task is not complete. 446 bool offer_termination() { 447 return offer_termination(NULL); 448 } 449 450 // As above, but it also terminates if the should_exit_termination() 451 // method of the terminator parameter returns true. If terminator is 452 // NULL, then it is ignored. 453 bool offer_termination(TerminatorTerminator* terminator); 454 455 // Reset the terminator, so that it may be reused again. 456 // The caller is responsible for ensuring that this is done 457 // in an MT-safe manner, once the previous round of use of 458 // the terminator is finished. 459 void reset_for_reuse(); 460 // Same as above but the number of parallel threads is set to the 461 // given number. 462 void reset_for_reuse(uint n_threads); 463 464 #ifdef TRACESPINNING 465 static uint total_yields() { return _total_yields; } 466 static uint total_spins() { return _total_spins; } 467 static uint total_peeks() { return _total_peeks; } 468 static void print_termination_counts(); 469 #endif 470 }; 471 472 typedef GenericTaskQueue<oop, mtGC> OopTaskQueue; 473 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet; 474 475 #ifdef _MSC_VER 476 #pragma warning(push) 477 // warning C4522: multiple assignment operators specified 478 #pragma warning(disable:4522) 479 #endif 480 481 // This is a container class for either an oop* or a narrowOop*. 482 // Both are pushed onto a task queue and the consumer will test is_narrow() 483 // to determine which should be processed. 484 class StarTask { 485 void* _holder; // either union oop* or narrowOop* 486 487 enum { COMPRESSED_OOP_MASK = 1 }; 488 489 public: 490 StarTask(narrowOop* p) { 491 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); 492 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK); 493 } 494 StarTask(oop* p) { 495 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); 496 _holder = (void*)p; 497 } 498 StarTask() { _holder = NULL; } 499 operator oop*() { return (oop*)_holder; } 500 operator narrowOop*() { 501 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK); 502 } 503 504 StarTask& operator=(const StarTask& t) { 505 _holder = t._holder; 506 return *this; 507 } 508 volatile StarTask& operator=(const volatile StarTask& t) volatile { 509 _holder = t._holder; 510 return *this; 511 } 512 513 bool is_narrow() const { 514 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0); 515 } 516 }; 517 518 class ObjArrayTask 519 { 520 public: 521 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { } 522 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) { 523 assert(idx <= size_t(max_jint), "too big"); 524 } 525 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { } 526 527 ObjArrayTask& operator =(const ObjArrayTask& t) { 528 _obj = t._obj; 529 _index = t._index; 530 return *this; 531 } 532 volatile ObjArrayTask& 533 operator =(const volatile ObjArrayTask& t) volatile { 534 (void)const_cast<oop&>(_obj = t._obj); 535 _index = t._index; 536 return *this; 537 } 538 539 inline oop obj() const { return _obj; } 540 inline int index() const { return _index; } 541 542 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid. 543 544 private: 545 oop _obj; 546 int _index; 547 }; 548 549 #ifdef _MSC_VER 550 #pragma warning(pop) 551 #endif 552 553 typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue; 554 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet; 555 556 typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue; 557 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet; 558 559 560 #endif // SHARE_VM_UTILITIES_TASKQUEUE_HPP