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
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  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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  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 
 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   uint size() const { return _n; }
 387 };
 388 
 389 template<class T, MEMFLAGS F> void
 390 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
 391   assert(i < _n, "index out of range.");
 392   _queues[i] = q;
 393 }
 394 
 395 template<class T, MEMFLAGS F> T*
 396 GenericTaskQueueSet<T, F>::queue(uint i) {
 397   return _queues[i];
 398 }
 399 
 400 template<class T, MEMFLAGS F>
 401 bool GenericTaskQueueSet<T, F>::peek() {
 402   // Try all the queues.
 403   for (uint j = 0; j < _n; j++) {
 404     if (_queues[j]->peek())
 405       return true;
 406   }
 407   return false;
 408 }
 409 
 410 // When to terminate from the termination protocol.
 411 class TerminatorTerminator: public CHeapObj<mtInternal> {
 412 public:
 413   virtual bool should_exit_termination() = 0;
 414 };
 415 
 416 // A class to aid in the termination of a set of parallel tasks using
 417 // TaskQueueSet's for work stealing.
 418 
 419 #undef TRACESPINNING
 420 
 421 class ParallelTaskTerminator: public StackObj {
 422 private:
 423   uint _n_threads;
 424   TaskQueueSetSuper* _queue_set;
 425   uint _offered_termination;
 426 
 427 #ifdef TRACESPINNING
 428   static uint _total_yields;
 429   static uint _total_spins;
 430   static uint _total_peeks;
 431 #endif
 432 
 433   bool peek_in_queue_set();
 434 protected:
 435   virtual void yield();
 436   void sleep(uint millis);
 437 
 438 public:
 439 
 440   // "n_threads" is the number of threads to be terminated.  "queue_set" is a
 441   // queue sets of work queues of other threads.
 442   ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);
 443 
 444   // The current thread has no work, and is ready to terminate if everyone
 445   // else is.  If returns "true", all threads are terminated.  If returns
 446   // "false", available work has been observed in one of the task queues,
 447   // so the global task is not complete.
 448   bool offer_termination() {
 449     return offer_termination(NULL);
 450   }
 451 
 452   // As above, but it also terminates if the should_exit_termination()
 453   // method of the terminator parameter returns true. If terminator is
 454   // NULL, then it is ignored.
 455   bool offer_termination(TerminatorTerminator* terminator);
 456 
 457   // Reset the terminator, so that it may be reused again.
 458   // The caller is responsible for ensuring that this is done
 459   // in an MT-safe manner, once the previous round of use of
 460   // the terminator is finished.
 461   void reset_for_reuse();
 462   // Same as above but the number of parallel threads is set to the
 463   // given number.
 464   void reset_for_reuse(uint n_threads);
 465 
 466 #ifdef TRACESPINNING
 467   static uint total_yields() { return _total_yields; }
 468   static uint total_spins() { return _total_spins; }
 469   static uint total_peeks() { return _total_peeks; }
 470   static void print_termination_counts();
 471 #endif
 472 };
 473 
 474 typedef GenericTaskQueue<oop, mtGC>             OopTaskQueue;
 475 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
 476 
 477 #ifdef _MSC_VER
 478 #pragma warning(push)
 479 // warning C4522: multiple assignment operators specified
 480 #pragma warning(disable:4522)
 481 #endif
 482 
 483 // This is a container class for either an oop* or a narrowOop*.
 484 // Both are pushed onto a task queue and the consumer will test is_narrow()
 485 // to determine which should be processed.
 486 class StarTask {
 487   void*  _holder;        // either union oop* or narrowOop*
 488 
 489   enum { COMPRESSED_OOP_MASK = 1 };
 490 
 491  public:
 492   StarTask(narrowOop* p) {
 493     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 494     _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
 495   }
 496   StarTask(oop* p)       {
 497     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 498     _holder = (void*)p;
 499   }
 500   StarTask()             { _holder = NULL; }
 501   operator oop*()        { return (oop*)_holder; }
 502   operator narrowOop*()  {
 503     return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
 504   }
 505 
 506   StarTask& operator=(const StarTask& t) {
 507     _holder = t._holder;
 508     return *this;
 509   }
 510   volatile StarTask& operator=(const volatile StarTask& t) volatile {
 511     _holder = t._holder;
 512     return *this;
 513   }
 514 
 515   bool is_narrow() const {
 516     return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
 517   }
 518 };
 519 
 520 class ObjArrayTask
 521 {
 522 public:
 523   ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
 524   ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
 525     assert(idx <= size_t(max_jint), "too big");
 526   }
 527   ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
 528 
 529   ObjArrayTask& operator =(const ObjArrayTask& t) {
 530     _obj = t._obj;
 531     _index = t._index;
 532     return *this;
 533   }
 534   volatile ObjArrayTask&
 535   operator =(const volatile ObjArrayTask& t) volatile {
 536     (void)const_cast<oop&>(_obj = t._obj);
 537     _index = t._index;
 538     return *this;
 539   }
 540 
 541   inline oop obj()   const { return _obj; }
 542   inline int index() const { return _index; }
 543 
 544   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 545 
 546 private:
 547   oop _obj;
 548   int _index;
 549 };
 550 
 551 #ifdef _MSC_VER
 552 #pragma warning(pop)
 553 #endif
 554 
 555 typedef OverflowTaskQueue<StarTask, mtClass>           OopStarTaskQueue;
 556 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet;
 557 
 558 typedef OverflowTaskQueue<size_t, mtInternal>             RegionTaskQueue;
 559 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass>     RegionTaskQueueSet;
 560 
 561 
 562 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP