1 /* 2 * Copyright (c) 2001, 2016, 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_GC_SHARED_TASKQUEUE_HPP 26 #define SHARE_VM_GC_SHARED_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 protected: 252 typedef typename TaskQueueSuper<N, F>::Age Age; 253 typedef typename TaskQueueSuper<N, F>::idx_t idx_t; 254 255 using TaskQueueSuper<N, F>::_bottom; 256 using TaskQueueSuper<N, F>::_age; 257 using TaskQueueSuper<N, F>::increment_index; 258 using TaskQueueSuper<N, F>::decrement_index; 259 using TaskQueueSuper<N, F>::dirty_size; 260 261 public: 262 using TaskQueueSuper<N, F>::max_elems; 263 using TaskQueueSuper<N, F>::size; 264 265 #if TASKQUEUE_STATS 266 using TaskQueueSuper<N, F>::stats; 267 #endif 268 269 private: 270 // Slow paths for push, pop_local. (pop_global has no fast path.) 271 bool push_slow(E t, uint dirty_n_elems); 272 bool pop_local_slow(uint localBot, Age oldAge); 273 274 public: 275 typedef E element_type; 276 277 // Initializes the queue to empty. 278 GenericTaskQueue(); 279 280 void initialize(); 281 282 // Push the task "t" on the queue. Returns "false" iff the queue is full. 283 inline bool push(E t); 284 285 // Attempts to claim a task from the "local" end of the queue (the most 286 // recently pushed). If successful, returns true and sets t to the task; 287 // otherwise, returns false (the queue is empty). 288 inline bool pop_local(volatile E& t); 289 290 // Like pop_local(), but uses the "global" end of the queue (the least 291 // recently pushed). 292 bool pop_global(volatile E& t); 293 294 // Delete any resource associated with the queue. 295 ~GenericTaskQueue(); 296 297 // Apply fn to each element in the task queue. The queue must not 298 // be modified while iterating. 299 template<typename Fn> void iterate(Fn fn); 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 // Try to push task t onto the queue only. Returns true if successful, false otherwise. 334 inline bool try_push_to_taskqueue(E t); 335 336 // Attempt to pop from the overflow stack; return true if anything was popped. 337 inline bool pop_overflow(E& t); 338 339 inline overflow_t* overflow_stack() { return &_overflow_stack; } 340 341 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); } 342 inline bool overflow_empty() const { return _overflow_stack.is_empty(); } 343 inline bool is_empty() const { 344 return taskqueue_empty() && overflow_empty(); 345 } 346 347 private: 348 overflow_t _overflow_stack; 349 }; 350 351 class TaskQueueSetSuper { 352 protected: 353 static int randomParkAndMiller(int* seed0); 354 public: 355 // Returns "true" if some TaskQueue in the set contains a task. 356 virtual bool peek() = 0; 357 }; 358 359 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper { 360 }; 361 362 template<class T, MEMFLAGS F> 363 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> { 364 private: 365 uint _n; 366 T** _queues; 367 368 public: 369 typedef typename T::element_type E; 370 371 GenericTaskQueueSet(int n); 372 373 bool steal_best_of_2(uint queue_num, int* seed, E& t); 374 375 void register_queue(uint i, T* q); 376 377 T* queue(uint n); 378 379 // The thread with queue number "queue_num" (and whose random number seed is 380 // at "seed") is trying to steal a task from some other queue. (It may try 381 // several queues, according to some configuration parameter.) If some steal 382 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns 383 // false. 384 bool steal(uint queue_num, int* seed, E& t); 385 386 bool peek(); 387 388 uint size() const { return _n; } 389 }; 390 391 template<class T, MEMFLAGS F> void 392 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) { 393 assert(i < _n, "index out of range."); 394 _queues[i] = q; 395 } 396 397 template<class T, MEMFLAGS F> T* 398 GenericTaskQueueSet<T, F>::queue(uint i) { 399 return _queues[i]; 400 } 401 402 template<class T, MEMFLAGS F> 403 bool GenericTaskQueueSet<T, F>::peek() { 404 // Try all the queues. 405 for (uint j = 0; j < _n; j++) { 406 if (_queues[j]->peek()) 407 return true; 408 } 409 return false; 410 } 411 412 // When to terminate from the termination protocol. 413 class TerminatorTerminator: public CHeapObj<mtInternal> { 414 public: 415 virtual bool should_exit_termination() = 0; 416 }; 417 418 // A class to aid in the termination of a set of parallel tasks using 419 // TaskQueueSet's for work stealing. 420 421 #undef TRACESPINNING 422 423 class ParallelTaskTerminator: public StackObj { 424 private: 425 uint _n_threads; 426 TaskQueueSetSuper* _queue_set; 427 uint _offered_termination; 428 429 #ifdef TRACESPINNING 430 static uint _total_yields; 431 static uint _total_spins; 432 static uint _total_peeks; 433 #endif 434 435 bool peek_in_queue_set(); 436 protected: 437 virtual void yield(); 438 void sleep(uint millis); 439 440 public: 441 442 // "n_threads" is the number of threads to be terminated. "queue_set" is a 443 // queue sets of work queues of other threads. 444 ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set); 445 446 // The current thread has no work, and is ready to terminate if everyone 447 // else is. If returns "true", all threads are terminated. If returns 448 // "false", available work has been observed in one of the task queues, 449 // so the global task is not complete. 450 bool offer_termination() { 451 return offer_termination(NULL); 452 } 453 454 // As above, but it also terminates if the should_exit_termination() 455 // method of the terminator parameter returns true. If terminator is 456 // NULL, then it is ignored. 457 bool offer_termination(TerminatorTerminator* terminator); 458 459 // Reset the terminator, so that it may be reused again. 460 // The caller is responsible for ensuring that this is done 461 // in an MT-safe manner, once the previous round of use of 462 // the terminator is finished. 463 void reset_for_reuse(); 464 // Same as above but the number of parallel threads is set to the 465 // given number. 466 void reset_for_reuse(uint n_threads); 467 468 #ifdef TRACESPINNING 469 static uint total_yields() { return _total_yields; } 470 static uint total_spins() { return _total_spins; } 471 static uint total_peeks() { return _total_peeks; } 472 static void print_termination_counts(); 473 #endif 474 }; 475 476 typedef GenericTaskQueue<oop, mtGC> OopTaskQueue; 477 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet; 478 479 #ifdef _MSC_VER 480 #pragma warning(push) 481 // warning C4522: multiple assignment operators specified 482 #pragma warning(disable:4522) 483 #endif 484 485 // This is a container class for either an oop* or a narrowOop*. 486 // Both are pushed onto a task queue and the consumer will test is_narrow() 487 // to determine which should be processed. 488 class StarTask { 489 void* _holder; // either union oop* or narrowOop* 490 491 enum { COMPRESSED_OOP_MASK = 1 }; 492 493 public: 494 StarTask(narrowOop* p) { 495 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); 496 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK); 497 } 498 StarTask(oop* p) { 499 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); 500 _holder = (void*)p; 501 } 502 StarTask() { _holder = NULL; } 503 operator oop*() { return (oop*)_holder; } 504 operator narrowOop*() { 505 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK); 506 } 507 508 StarTask& operator=(const StarTask& t) { 509 _holder = t._holder; 510 return *this; 511 } 512 volatile StarTask& operator=(const volatile StarTask& t) volatile { 513 _holder = t._holder; 514 return *this; 515 } 516 517 bool is_narrow() const { 518 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0); 519 } 520 }; 521 522 class ObjArrayTask 523 { 524 public: 525 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { } 526 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) { 527 assert(idx <= size_t(max_jint), "too big"); 528 } 529 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { } 530 531 ObjArrayTask& operator =(const ObjArrayTask& t) { 532 _obj = t._obj; 533 _index = t._index; 534 return *this; 535 } 536 volatile ObjArrayTask& 537 operator =(const volatile ObjArrayTask& t) volatile { 538 (void)const_cast<oop&>(_obj = t._obj); 539 _index = t._index; 540 return *this; 541 } 542 543 inline oop obj() const { return _obj; } 544 inline int index() const { return _index; } 545 546 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid. 547 548 private: 549 oop _obj; 550 int _index; 551 }; 552 553 #ifdef _MSC_VER 554 #pragma warning(pop) 555 #endif 556 557 typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue; 558 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet; 559 560 typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue; 561 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet; 562 563 564 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP