1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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.
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  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).
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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 "oops/oopsHierarchy.hpp"
  30 #include "utilities/ostream.hpp"
  31 #include "utilities/stack.hpp"
  32 
  33 // Simple TaskQueue stats that are collected by default in debug builds.
  34 
  35 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
  36 #define TASKQUEUE_STATS 1
  37 #elif !defined(TASKQUEUE_STATS)
  38 #define TASKQUEUE_STATS 1
  39 #endif
  40 
  41 #if TASKQUEUE_STATS
  42 #define TASKQUEUE_STATS_ONLY(code) code
  43 #else
  44 #define TASKQUEUE_STATS_ONLY(code)
  45 #endif // TASKQUEUE_STATS
  46 
  47 #if TASKQUEUE_STATS
  48 class TaskQueueStats {
  49 public:
  50   enum StatId {
  51     push,             // number of taskqueue pushes
  52     pop,              // number of taskqueue pops
  53     pop_slow,         // subset of taskqueue pops that were done slow-path
  54     steal_attempt,    // number of taskqueue steal attempts
  55     steal,            // number of taskqueue steals
  56     overflow,         // number of overflow pushes
  57     overflow_max_len, // max length of overflow stack
  58     last_stat_id
  59   };
  60 
  61 public:
  62   inline TaskQueueStats()       { reset(); }
  63 
  64   inline void record_push()          { ++_stats[push]; }
  65   inline void record_pop()           { ++_stats[pop]; }
  66   inline void record_pop_slow()      { record_pop(); ++_stats[pop_slow]; }
  67   inline void record_steal_attempt() { ++_stats[steal_attempt]; }
  68   inline void record_steal()         { ++_stats[steal]; }
  69   inline void record_overflow(size_t new_length);
  70 
  71   TaskQueueStats & operator +=(const TaskQueueStats & addend);
  72 
  73   inline size_t get(StatId id) const { return _stats[id]; }
  74   inline const size_t* get() const   { return _stats; }
  75 
  76   inline void reset();
  77 
  78   // Print the specified line of the header (does not include a line separator).
  79   static void print_header(unsigned int line, outputStream* const stream = tty,
  80                            unsigned int width = 10);
  81   // Print the statistics (does not include a line separator).
  82   void print(outputStream* const stream = tty, unsigned int width = 10) const;
  83 
  84   DEBUG_ONLY(void verify() const;)
  85 
  86 private:
  87   size_t                    _stats[last_stat_id];
  88   static const char * const _names[last_stat_id];
  89 };
  90 
  91 void TaskQueueStats::record_overflow(size_t new_len) {
  92   ++_stats[overflow];
  93   if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
  94 }
  95 
  96 void TaskQueueStats::reset() {
  97   memset(_stats, 0, sizeof(_stats));
  98 }
  99 #endif // TASKQUEUE_STATS
 100 
 101 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
 102 
 103 template <unsigned int N, MEMFLAGS F>
 104 class TaskQueueSuper: public CHeapObj<F> {
 105 protected:
 106   // Internal type for indexing the queue; also used for the tag.
 107   typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
 108 
 109   // The first free element after the last one pushed (mod N).
 110   volatile uint _bottom;
 111 
 112   enum { MOD_N_MASK = N - 1 };
 113 
 114   class Age {
 115   public:
 116     Age(size_t data = 0)         { _data = data; }
 117     Age(const Age& age)          { _data = age._data; }
 118     Age(idx_t top, idx_t tag)    { _fields._top = top; _fields._tag = tag; }
 119 
 120     Age   get()        const volatile { return _data; }
 121     void  set(Age age) volatile       { _data = age._data; }
 122 
 123     idx_t top()        const volatile { return _fields._top; }
 124     idx_t tag()        const volatile { return _fields._tag; }
 125 
 126     // Increment top; if it wraps, increment tag also.
 127     void increment() {
 128       _fields._top = increment_index(_fields._top);
 129       if (_fields._top == 0) ++_fields._tag;
 130     }
 131 
 132     Age cmpxchg(const Age new_age, const Age old_age) volatile;
 133 
 134     bool operator ==(const Age& other) const { return _data == other._data; }
 135 
 136   private:
 137     struct fields {
 138       idx_t _top;
 139       idx_t _tag;
 140     };
 141     union {
 142       size_t _data;
 143       fields _fields;
 144     };
 145   };
 146 
 147   volatile Age _age;
 148 
 149   // These both operate mod N.
 150   static uint increment_index(uint ind) {
 151     return (ind + 1) & MOD_N_MASK;
 152   }
 153   static uint decrement_index(uint ind) {
 154     return (ind - 1) & MOD_N_MASK;
 155   }
 156 
 157   // Returns a number in the range [0..N).  If the result is "N-1", it should be
 158   // interpreted as 0.
 159   uint dirty_size(uint bot, uint top) const {
 160     return (bot - top) & MOD_N_MASK;
 161   }
 162 
 163   // Returns the size corresponding to the given "bot" and "top".
 164   uint size(uint bot, uint top) const {
 165     uint sz = dirty_size(bot, top);
 166     // Has the queue "wrapped", so that bottom is less than top?  There's a
 167     // complicated special case here.  A pair of threads could perform pop_local
 168     // and pop_global operations concurrently, starting from a state in which
 169     // _bottom == _top+1.  The pop_local could succeed in decrementing _bottom,
 170     // and the pop_global in incrementing _top (in which case the pop_global
 171     // will be awarded the contested queue element.)  The resulting state must
 172     // be interpreted as an empty queue.  (We only need to worry about one such
 173     // event: only the queue owner performs pop_local's, and several concurrent
 174     // threads attempting to perform the pop_global will all perform the same
 175     // CAS, and only one can succeed.)  Any stealing thread that reads after
 176     // either the increment or decrement will see an empty queue, and will not
 177     // join the competitors.  The "sz == -1 || sz == N-1" state will not be
 178     // modified by concurrent queues, so the owner thread can reset the state to
 179     // _bottom == top so subsequent pushes will be performed normally.
 180     return (sz == N - 1) ? 0 : sz;
 181   }
 182 
 183 public:
 184   TaskQueueSuper() : _bottom(0), _age() {}
 185 
 186   // Return true if the TaskQueue contains/does not contain any tasks.
 187   bool peek()     const { return _bottom != _age.top(); }
 188   bool is_empty() const { return size() == 0; }
 189 
 190   // Return an estimate of the number of elements in the queue.
 191   // The "careful" version admits the possibility of pop_local/pop_global
 192   // races.
 193   uint size() const {
 194     return size(_bottom, _age.top());
 195   }
 196 
 197   uint dirty_size() const {
 198     return dirty_size(_bottom, _age.top());
 199   }
 200 
 201   void set_empty() {
 202     _bottom = 0;
 203     _age.set(0);
 204   }
 205 
 206   // Maximum number of elements allowed in the queue.  This is two less
 207   // than the actual queue size, for somewhat complicated reasons.
 208   uint max_elems() const { return N - 2; }
 209 
 210   // Total size of queue.
 211   static const uint total_size() { return N; }
 212 
 213   TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
 214 };
 215 
 216 //
 217 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
 218 // ended-queue (deque), intended for use in work stealing. Queue operations
 219 // are non-blocking.
 220 //
 221 // A queue owner thread performs push() and pop_local() operations on one end
 222 // of the queue, while other threads may steal work using the pop_global()
 223 // method.
 224 //
 225 // The main difference to the original algorithm is that this
 226 // implementation allows wrap-around at the end of its allocated
 227 // storage, which is an array.
 228 //
 229 // The original paper is:
 230 //
 231 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
 232 // Thread scheduling for multiprogrammed multiprocessors.
 233 // Theory of Computing Systems 34, 2 (2001), 115-144.
 234 //
 235 // The following paper provides an correctness proof and an
 236 // implementation for weakly ordered memory models including (pseudo-)
 237 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
 238 // similar to ABP, with the main difference that it allows resizing of the
 239 // underlying storage:
 240 //
 241 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
 242 // Correct and efficient work-stealing for weak memory models
 243 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
 244 // practice of parallel programming (PPoPP 2013), 69-80
 245 //
 246 
 247 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 248 class GenericTaskQueue: public TaskQueueSuper<N, F> {
 249 protected:
 250   typedef typename TaskQueueSuper<N, F>::Age Age;
 251   typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
 252 
 253   using TaskQueueSuper<N, F>::_bottom;
 254   using TaskQueueSuper<N, F>::_age;
 255   using TaskQueueSuper<N, F>::increment_index;
 256   using TaskQueueSuper<N, F>::decrement_index;
 257   using TaskQueueSuper<N, F>::dirty_size;
 258 
 259 public:
 260   using TaskQueueSuper<N, F>::max_elems;
 261   using TaskQueueSuper<N, F>::size;
 262 
 263 #if  TASKQUEUE_STATS
 264   using TaskQueueSuper<N, F>::stats;
 265 #endif
 266 
 267 private:
 268   // Slow paths for push, pop_local.  (pop_global has no fast path.)
 269   bool push_slow(E t, uint dirty_n_elems);
 270   bool pop_local_slow(uint localBot, Age oldAge);
 271 
 272 public:
 273   typedef E element_type;
 274 
 275   // Initializes the queue to empty.
 276   GenericTaskQueue();
 277 
 278   void initialize();
 279 
 280   // Push the task "t" on the queue.  Returns "false" iff the queue is full.
 281   inline bool push(E t);
 282 
 283   // Attempts to claim a task from the "local" end of the queue (the most
 284   // recently pushed) as long as the number of entries exceeds the threshold.
 285   // If successful, returns true and sets t to the task; otherwise, returns false
 286   // (the queue is empty or the number of elements below the threshold).
 287   inline bool pop_local(volatile E& t, uint threshold = 0);
 288 
 289   // Like pop_local(), but uses the "global" end of the queue (the least
 290   // recently pushed).
 291   bool pop_global(volatile E& t);
 292 
 293   // Delete any resource associated with the queue.
 294   ~GenericTaskQueue();
 295 
 296   // Apply fn to each element in the task queue.  The queue must not
 297   // be modified while iterating.
 298   template<typename Fn> void iterate(Fn fn);
 299 
 300 private:
 301   // Element array.
 302   volatile E* _elems;
 303 };
 304 
 305 template<class E, MEMFLAGS F, unsigned int N>
 306 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
 307   assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
 308 }
 309 
 310 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
 311 // elements that do not fit in the TaskQueue.
 312 //
 313 // This class hides two methods from super classes:
 314 //
 315 // push() - push onto the task queue or, if that fails, onto the overflow stack
 316 // is_empty() - return true if both the TaskQueue and overflow stack are empty
 317 //
 318 // Note that size() is not hidden--it returns the number of elements in the
 319 // TaskQueue, and does not include the size of the overflow stack.  This
 320 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
 321 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 322 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
 323 {
 324 public:
 325   typedef Stack<E, F>               overflow_t;
 326   typedef GenericTaskQueue<E, F, N> taskqueue_t;
 327 
 328   TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
 329 
 330   // Push task t onto the queue or onto the overflow stack.  Return true.
 331   inline bool push(E t);
 332   // Try to push task t onto the queue only. Returns true if successful, false otherwise.
 333   inline bool try_push_to_taskqueue(E t);
 334 
 335   // Attempt to pop from the overflow stack; return true if anything was popped.
 336   inline bool pop_overflow(E& t);
 337 
 338   inline overflow_t* overflow_stack() { return &_overflow_stack; }
 339 
 340   inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
 341   inline bool overflow_empty()  const { return _overflow_stack.is_empty(); }
 342   inline bool is_empty()        const {
 343     return taskqueue_empty() && overflow_empty();
 344   }
 345 
 346 private:
 347   overflow_t _overflow_stack;
 348 };
 349 
 350 class TaskQueueSetSuper {
 351 protected:
 352   static int randomParkAndMiller(int* seed0);
 353 public:
 354   // Returns "true" if some TaskQueue in the set contains a task.
 355   virtual bool peek() = 0;
 356 };
 357 
 358 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
 359 };
 360 
 361 template<class T, MEMFLAGS F>
 362 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
 363 public:
 364   typedef typename T::element_type E;
 365 
 366 private:
 367   uint _n;
 368   T** _queues;
 369 
 370   bool steal_best_of_2(uint queue_num, int* seed, E& t);
 371 
 372 public:
 373   GenericTaskQueueSet(int n);
 374   ~GenericTaskQueueSet();
 375 
 376   void register_queue(uint i, T* q);
 377 
 378   T* queue(uint n);
 379 
 380   // The thread with queue number "queue_num" (and whose random number seed is
 381   // at "seed") is trying to steal a task from some other queue.  (It may try
 382   // several queues, according to some configuration parameter.)  If some steal
 383   // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
 384   // false.
 385   bool steal(uint queue_num, int* seed, E& t);
 386 
 387   bool peek();
 388 
 389   uint size() const { return _n; }
 390 };
 391 
 392 template<class T, MEMFLAGS F> void
 393 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
 394   assert(i < _n, "index out of range.");
 395   _queues[i] = q;
 396 }
 397 
 398 template<class T, MEMFLAGS F> T*
 399 GenericTaskQueueSet<T, F>::queue(uint i) {
 400   return _queues[i];
 401 }
 402 
 403 template<class T, MEMFLAGS F>
 404 bool GenericTaskQueueSet<T, F>::peek() {
 405   // Try all the queues.
 406   for (uint j = 0; j < _n; j++) {
 407     if (_queues[j]->peek())
 408       return true;
 409   }
 410   return false;
 411 }
 412 
 413 // When to terminate from the termination protocol.
 414 class TerminatorTerminator: public CHeapObj<mtInternal> {
 415 public:
 416   virtual bool should_exit_termination() = 0;
 417 };
 418 
 419 // A class to aid in the termination of a set of parallel tasks using
 420 // TaskQueueSet's for work stealing.
 421 
 422 #undef TRACESPINNING
 423 
 424 class ParallelTaskTerminator: public StackObj {
 425 private:
 426   uint _n_threads;
 427   TaskQueueSetSuper* _queue_set;
 428   volatile uint _offered_termination;
 429 
 430 #ifdef TRACESPINNING
 431   static uint _total_yields;
 432   static uint _total_spins;
 433   static uint _total_peeks;
 434 #endif
 435 
 436   bool peek_in_queue_set();
 437 protected:
 438   virtual void yield();
 439   void sleep(uint millis);
 440 
 441 public:
 442 
 443   // "n_threads" is the number of threads to be terminated.  "queue_set" is a
 444   // queue sets of work queues of other threads.
 445   ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);
 446 
 447   // The current thread has no work, and is ready to terminate if everyone
 448   // else is.  If returns "true", all threads are terminated.  If returns
 449   // "false", available work has been observed in one of the task queues,
 450   // so the global task is not complete.
 451   bool offer_termination() {
 452     return offer_termination(NULL);
 453   }
 454 
 455   // As above, but it also terminates if the should_exit_termination()
 456   // method of the terminator parameter returns true. If terminator is
 457   // NULL, then it is ignored.
 458   bool offer_termination(TerminatorTerminator* terminator);
 459 
 460   // Reset the terminator, so that it may be reused again.
 461   // The caller is responsible for ensuring that this is done
 462   // in an MT-safe manner, once the previous round of use of
 463   // the terminator is finished.
 464   void reset_for_reuse();
 465   // Same as above but the number of parallel threads is set to the
 466   // given number.
 467   void reset_for_reuse(uint n_threads);
 468 
 469 #ifdef TRACESPINNING
 470   static uint total_yields() { return _total_yields; }
 471   static uint total_spins() { return _total_spins; }
 472   static uint total_peeks() { return _total_peeks; }
 473   static void print_termination_counts();
 474 #endif
 475 };
 476 
 477 typedef GenericTaskQueue<oop, mtGC>             OopTaskQueue;
 478 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
 479 
 480 #ifdef _MSC_VER
 481 #pragma warning(push)
 482 // warning C4522: multiple assignment operators specified
 483 #pragma warning(disable:4522)
 484 #endif
 485 
 486 // This is a container class for either an oop* or a narrowOop*.
 487 // Both are pushed onto a task queue and the consumer will test is_narrow()
 488 // to determine which should be processed.
 489 class StarTask {
 490   void*  _holder;        // either union oop* or narrowOop*
 491 
 492   enum { COMPRESSED_OOP_MASK = 1 };
 493 
 494  public:
 495   StarTask(narrowOop* p) {
 496     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 497     _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
 498   }
 499   StarTask(oop* p)       {
 500     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 501     _holder = (void*)p;
 502   }
 503   StarTask()             { _holder = NULL; }
 504   operator oop*()        { return (oop*)_holder; }
 505   operator narrowOop*()  {
 506     return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
 507   }
 508 
 509   StarTask& operator=(const StarTask& t) {
 510     _holder = t._holder;
 511     return *this;
 512   }
 513   volatile StarTask& operator=(const volatile StarTask& t) volatile {
 514     _holder = t._holder;
 515     return *this;
 516   }
 517 
 518   bool is_narrow() const {
 519     return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
 520   }
 521 };
 522 
 523 class ObjArrayTask
 524 {
 525 public:
 526   ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
 527   ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
 528     assert(idx <= size_t(max_jint), "too big");
 529   }
 530   ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
 531 
 532   ObjArrayTask& operator =(const ObjArrayTask& t) {
 533     _obj = t._obj;
 534     _index = t._index;
 535     return *this;
 536   }
 537   volatile ObjArrayTask&
 538   operator =(const volatile ObjArrayTask& t) volatile {
 539     (void)const_cast<oop&>(_obj = t._obj);
 540     _index = t._index;
 541     return *this;
 542   }
 543 
 544   inline oop obj()   const { return _obj; }
 545   inline int index() const { return _index; }
 546 
 547   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 548 
 549 private:
 550   oop _obj;
 551   int _index;
 552 };
 553 
 554 #ifdef _MSC_VER
 555 #pragma warning(pop)
 556 #endif
 557 
 558 typedef OverflowTaskQueue<StarTask, mtGC>           OopStarTaskQueue;
 559 typedef GenericTaskQueueSet<OopStarTaskQueue, mtGC> OopStarTaskQueueSet;
 560 
 561 typedef OverflowTaskQueue<size_t, mtGC>             RegionTaskQueue;
 562 typedef GenericTaskQueueSet<RegionTaskQueue, mtGC>  RegionTaskQueueSet;
 563 
 564 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP