1 /*
   2  * Copyright (c) 2001, 2018, 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.
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   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.
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  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 "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 0
  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(bool success);
  68   inline void record_overflow(size_t new_length);
  69 
  70   TaskQueueStats & operator +=(const TaskQueueStats & addend);
  71 
  72   inline size_t get(StatId id) const { return _stats[id]; }
  73   inline const size_t* get() const   { return _stats; }
  74 
  75   inline void reset();
  76 
  77   // Print the specified line of the header (does not include a line separator).
  78   static void print_header(unsigned int line, outputStream* const stream = tty,
  79                            unsigned int width = 10);
  80   // Print the statistics (does not include a line separator).
  81   void print(outputStream* const stream = tty, unsigned int width = 10) const;
  82 
  83   DEBUG_ONLY(void verify() const;)
  84 
  85 private:
  86   size_t                    _stats[last_stat_id];
  87   static const char * const _names[last_stat_id];
  88 };
  89 
  90 void TaskQueueStats::record_steal(bool success) {
  91   ++_stats[steal_attempt];
  92   if (success) ++_stats[steal];
  93 }
  94 
  95 void TaskQueueStats::record_overflow(size_t new_len) {
  96   ++_stats[overflow];
  97   if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
  98 }
  99 
 100 void TaskQueueStats::reset() {
 101   memset(_stats, 0, sizeof(_stats));
 102 }
 103 #endif // TASKQUEUE_STATS
 104 
 105 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
 106 
 107 template <unsigned int N, MEMFLAGS F>
 108 class TaskQueueSuper: public CHeapObj<F> {
 109 protected:
 110   // Internal type for indexing the queue; also used for the tag.
 111   typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
 112 
 113   // The first free element after the last one pushed (mod N).
 114   volatile uint _bottom;
 115 
 116   enum { MOD_N_MASK = N - 1 };
 117 
 118   class Age {
 119   public:
 120     Age(size_t data = 0)         { _data = data; }
 121     Age(const Age& age)          { _data = age._data; }
 122     Age(idx_t top, idx_t tag)    { _fields._top = top; _fields._tag = tag; }
 123 
 124     Age   get()        const volatile { return _data; }
 125     void  set(Age age) volatile       { _data = age._data; }
 126 
 127     idx_t top()        const volatile { return _fields._top; }
 128     idx_t tag()        const volatile { return _fields._tag; }
 129 
 130     // Increment top; if it wraps, increment tag also.
 131     void increment() {
 132       _fields._top = increment_index(_fields._top);
 133       if (_fields._top == 0) ++_fields._tag;
 134     }
 135 
 136     Age cmpxchg(const Age new_age, const Age old_age) volatile;
 137 
 138     bool operator ==(const Age& other) const { return _data == other._data; }
 139 
 140   private:
 141     struct fields {
 142       idx_t _top;
 143       idx_t _tag;
 144     };
 145     union {
 146       size_t _data;
 147       fields _fields;
 148     };
 149   };
 150 
 151   volatile Age _age;
 152 
 153   // These both operate mod N.
 154   static uint increment_index(uint ind) {
 155     return (ind + 1) & MOD_N_MASK;
 156   }
 157   static uint decrement_index(uint ind) {
 158     return (ind - 1) & MOD_N_MASK;
 159   }
 160 
 161   // Returns a number in the range [0..N).  If the result is "N-1", it should be
 162   // interpreted as 0.
 163   uint dirty_size(uint bot, uint top) const {
 164     return (bot - top) & MOD_N_MASK;
 165   }
 166 
 167   // Returns the size corresponding to the given "bot" and "top".
 168   uint size(uint bot, uint top) const {
 169     uint sz = dirty_size(bot, top);
 170     // Has the queue "wrapped", so that bottom is less than top?  There's a
 171     // complicated special case here.  A pair of threads could perform pop_local
 172     // and pop_global operations concurrently, starting from a state in which
 173     // _bottom == _top+1.  The pop_local could succeed in decrementing _bottom,
 174     // and the pop_global in incrementing _top (in which case the pop_global
 175     // will be awarded the contested queue element.)  The resulting state must
 176     // be interpreted as an empty queue.  (We only need to worry about one such
 177     // event: only the queue owner performs pop_local's, and several concurrent
 178     // threads attempting to perform the pop_global will all perform the same
 179     // CAS, and only one can succeed.)  Any stealing thread that reads after
 180     // either the increment or decrement will see an empty queue, and will not
 181     // join the competitors.  The "sz == -1 || sz == N-1" state will not be
 182     // modified by concurrent queues, so the owner thread can reset the state to
 183     // _bottom == top so subsequent pushes will be performed normally.
 184     return (sz == N - 1) ? 0 : sz;
 185   }
 186 
 187 public:
 188   TaskQueueSuper() : _bottom(0), _age() {}
 189 
 190   // Return true if the TaskQueue contains/does not contain any tasks.
 191   bool peek()     const { return _bottom != _age.top(); }
 192   bool is_empty() const { return size() == 0; }
 193 
 194   // Return an estimate of the number of elements in the queue.
 195   // The "careful" version admits the possibility of pop_local/pop_global
 196   // races.
 197   uint size() const {
 198     return size(_bottom, _age.top());
 199   }
 200 
 201   uint dirty_size() const {
 202     return dirty_size(_bottom, _age.top());
 203   }
 204 
 205   void set_empty() {
 206     _bottom = 0;
 207     _age.set(0);
 208   }
 209 
 210   // Maximum number of elements allowed in the queue.  This is two less
 211   // than the actual queue size, for somewhat complicated reasons.
 212   uint max_elems() const { return N - 2; }
 213 
 214   // Total size of queue.
 215   static const uint total_size() { return N; }
 216 
 217   TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
 218 };
 219 
 220 //
 221 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
 222 // ended-queue (deque), intended for use in work stealing. Queue operations
 223 // are non-blocking.
 224 //
 225 // A queue owner thread performs push() and pop_local() operations on one end
 226 // of the queue, while other threads may steal work using the pop_global()
 227 // method.
 228 //
 229 // The main difference to the original algorithm is that this
 230 // implementation allows wrap-around at the end of its allocated
 231 // storage, which is an array.
 232 //
 233 // The original paper is:
 234 //
 235 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
 236 // Thread scheduling for multiprogrammed multiprocessors.
 237 // Theory of Computing Systems 34, 2 (2001), 115-144.
 238 //
 239 // The following paper provides an correctness proof and an
 240 // implementation for weakly ordered memory models including (pseudo-)
 241 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
 242 // similar to ABP, with the main difference that it allows resizing of the
 243 // underlying storage:
 244 //
 245 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
 246 // Correct and efficient work-stealing for weak memory models
 247 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
 248 // practice of parallel programming (PPoPP 2013), 69-80
 249 //
 250 
 251 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 252 class GenericTaskQueue: public TaskQueueSuper<N, F> {
 253 protected:
 254   typedef typename TaskQueueSuper<N, F>::Age Age;
 255   typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
 256 
 257   using TaskQueueSuper<N, F>::_bottom;
 258   using TaskQueueSuper<N, F>::_age;
 259   using TaskQueueSuper<N, F>::increment_index;
 260   using TaskQueueSuper<N, F>::decrement_index;
 261   using TaskQueueSuper<N, F>::dirty_size;
 262 
 263 public:
 264   using TaskQueueSuper<N, F>::max_elems;
 265   using TaskQueueSuper<N, F>::size;
 266 
 267 #if  TASKQUEUE_STATS
 268   using TaskQueueSuper<N, F>::stats;
 269 #endif
 270 
 271 private:
 272   // Slow paths for push, pop_local.  (pop_global has no fast path.)
 273   bool push_slow(E t, uint dirty_n_elems);
 274   bool pop_local_slow(uint localBot, Age oldAge);
 275 
 276 public:
 277   typedef E element_type;
 278 
 279   // Initializes the queue to empty.
 280   GenericTaskQueue();
 281 
 282   void initialize();
 283 
 284   // Push the task "t" on the queue.  Returns "false" iff the queue is full.
 285   inline bool push(E t);
 286 
 287   // Attempts to claim a task from the "local" end of the queue (the most
 288   // recently pushed) as long as the number of entries exceeds the threshold.
 289   // If successful, returns true and sets t to the task; otherwise, returns false
 290   // (the queue is empty or the number of elements below the threshold).
 291   inline bool pop_local(volatile E& t, uint threshold = 0);
 292 
 293   // Like pop_local(), but uses the "global" end of the queue (the least
 294   // recently pushed).
 295   bool pop_global(volatile E& t);
 296 
 297   // Delete any resource associated with the queue.
 298   ~GenericTaskQueue();
 299 
 300   // Apply fn to each element in the task queue.  The queue must not
 301   // be modified while iterating.
 302   template<typename Fn> void iterate(Fn fn);
 303 
 304 private:
 305   // Element array.
 306   volatile E* _elems;
 307 };
 308 
 309 template<class E, MEMFLAGS F, unsigned int N>
 310 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
 311   assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
 312 }
 313 
 314 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
 315 // elements that do not fit in the TaskQueue.
 316 //
 317 // This class hides two methods from super classes:
 318 //
 319 // push() - push onto the task queue or, if that fails, onto the overflow stack
 320 // is_empty() - return true if both the TaskQueue and overflow stack are empty
 321 //
 322 // Note that size() is not hidden--it returns the number of elements in the
 323 // TaskQueue, and does not include the size of the overflow stack.  This
 324 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
 325 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 326 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
 327 {
 328 public:
 329   typedef Stack<E, F>               overflow_t;
 330   typedef GenericTaskQueue<E, F, N> taskqueue_t;
 331 
 332   TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
 333 
 334   // Push task t onto the queue or onto the overflow stack.  Return true.
 335   inline bool push(E t);
 336   // Try to push task t onto the queue only. Returns true if successful, false otherwise.
 337   inline bool try_push_to_taskqueue(E t);
 338 
 339   // Attempt to pop from the overflow stack; return true if anything was popped.
 340   inline bool pop_overflow(E& t);
 341 
 342   inline overflow_t* overflow_stack() { return &_overflow_stack; }
 343 
 344   inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
 345   inline bool overflow_empty()  const { return _overflow_stack.is_empty(); }
 346   inline bool is_empty()        const {
 347     return taskqueue_empty() && overflow_empty();
 348   }
 349 
 350 private:
 351   overflow_t _overflow_stack;
 352 };
 353 
 354 class TaskQueueSetSuper {
 355 protected:
 356   static int randomParkAndMiller(int* seed0);
 357 public:
 358   // Returns "true" if some TaskQueue in the set contains a task.
 359   virtual bool peek() = 0;
 360 };
 361 
 362 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
 363 };
 364 
 365 template<class T, MEMFLAGS F>
 366 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
 367 private:
 368   uint _n;
 369   T** _queues;
 370 
 371 public:
 372   typedef typename T::element_type E;
 373 
 374   GenericTaskQueueSet(int n);
 375   ~GenericTaskQueueSet();
 376 
 377   bool steal_best_of_2(uint queue_num, int* seed, E& t);
 378 
 379   void register_queue(uint i, T* q);
 380 
 381   T* queue(uint n);
 382 
 383   // The thread with queue number "queue_num" (and whose random number seed is
 384   // at "seed") is trying to steal a task from some other queue.  (It may try
 385   // several queues, according to some configuration parameter.)  If some steal
 386   // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
 387   // false.
 388   bool steal(uint queue_num, int* seed, E& t);
 389 
 390   bool peek();
 391 
 392   uint size() const { return _n; }
 393 };
 394 
 395 template<class T, MEMFLAGS F> void
 396 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
 397   assert(i < _n, "index out of range.");
 398   _queues[i] = q;
 399 }
 400 
 401 template<class T, MEMFLAGS F> T*
 402 GenericTaskQueueSet<T, F>::queue(uint i) {
 403   return _queues[i];
 404 }
 405 
 406 template<class T, MEMFLAGS F>
 407 bool GenericTaskQueueSet<T, F>::peek() {
 408   // Try all the queues.
 409   for (uint j = 0; j < _n; j++) {
 410     if (_queues[j]->peek())
 411       return true;
 412   }
 413   return false;
 414 }
 415 
 416 // When to terminate from the termination protocol.
 417 class TerminatorTerminator: public CHeapObj<mtInternal> {
 418 public:
 419   virtual bool should_exit_termination() = 0;
 420 };
 421 
 422 // A class to aid in the termination of a set of parallel tasks using
 423 // TaskQueueSet's for work stealing.
 424 
 425 #undef TRACESPINNING
 426 
 427 class ParallelTaskTerminator: public StackObj {
 428 private:
 429   uint _n_threads;
 430   TaskQueueSetSuper* _queue_set;
 431   volatile uint _offered_termination;
 432 
 433 #ifdef TRACESPINNING
 434   static uint _total_yields;
 435   static uint _total_spins;
 436   static uint _total_peeks;
 437 #endif
 438 
 439   bool peek_in_queue_set();
 440 protected:
 441   virtual void yield();
 442   void sleep(uint millis);
 443 
 444 public:
 445 
 446   // "n_threads" is the number of threads to be terminated.  "queue_set" is a
 447   // queue sets of work queues of other threads.
 448   ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);
 449 
 450   // The current thread has no work, and is ready to terminate if everyone
 451   // else is.  If returns "true", all threads are terminated.  If returns
 452   // "false", available work has been observed in one of the task queues,
 453   // so the global task is not complete.
 454   bool offer_termination() {
 455     return offer_termination(NULL);
 456   }
 457 
 458   // As above, but it also terminates if the should_exit_termination()
 459   // method of the terminator parameter returns true. If terminator is
 460   // NULL, then it is ignored.
 461   bool offer_termination(TerminatorTerminator* terminator);
 462 
 463   // Reset the terminator, so that it may be reused again.
 464   // The caller is responsible for ensuring that this is done
 465   // in an MT-safe manner, once the previous round of use of
 466   // the terminator is finished.
 467   void reset_for_reuse();
 468   // Same as above but the number of parallel threads is set to the
 469   // given number.
 470   void reset_for_reuse(uint n_threads);
 471 
 472 #ifdef TRACESPINNING
 473   static uint total_yields() { return _total_yields; }
 474   static uint total_spins() { return _total_spins; }
 475   static uint total_peeks() { return _total_peeks; }
 476   static void print_termination_counts();
 477 #endif
 478 };
 479 
 480 typedef GenericTaskQueue<oop, mtGC>             OopTaskQueue;
 481 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
 482 
 483 #ifdef _MSC_VER
 484 #pragma warning(push)
 485 // warning C4522: multiple assignment operators specified
 486 #pragma warning(disable:4522)
 487 #endif
 488 
 489 // This is a container class for either an oop* or a narrowOop*.
 490 // Both are pushed onto a task queue and the consumer will test is_narrow()
 491 // to determine which should be processed.
 492 class StarTask {
 493   void*  _holder;        // either union oop* or narrowOop*
 494 
 495   enum { COMPRESSED_OOP_MASK = 1 };
 496 
 497  public:
 498   StarTask(narrowOop* p) {
 499     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 500     _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
 501   }
 502   StarTask(oop* p)       {
 503     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 504     _holder = (void*)p;
 505   }
 506   StarTask()             { _holder = NULL; }
 507   operator oop*()        { return (oop*)_holder; }
 508   operator narrowOop*()  {
 509     return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
 510   }
 511 
 512   StarTask& operator=(const StarTask& t) {
 513     _holder = t._holder;
 514     return *this;
 515   }
 516   volatile StarTask& operator=(const volatile StarTask& t) volatile {
 517     _holder = t._holder;
 518     return *this;
 519   }
 520 
 521   bool is_narrow() const {
 522     return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
 523   }
 524 };
 525 
 526 class ObjArrayTask
 527 {
 528 public:
 529   ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
 530   ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
 531     assert(idx <= size_t(max_jint), "too big");
 532   }
 533   ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
 534 
 535   ObjArrayTask& operator =(const ObjArrayTask& t) {
 536     _obj = t._obj;
 537     _index = t._index;
 538     return *this;
 539   }
 540   volatile ObjArrayTask&
 541   operator =(const volatile ObjArrayTask& t) volatile {
 542     (void)const_cast<oop&>(_obj = t._obj);
 543     _index = t._index;
 544     return *this;
 545   }
 546 
 547   inline oop obj()   const { return _obj; }
 548   inline int index() const { return _index; }
 549 
 550   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 551 
 552 private:
 553   oop _obj;
 554   int _index;
 555 };
 556 
 557 #ifdef _MSC_VER
 558 #pragma warning(pop)
 559 #endif
 560 
 561 typedef OverflowTaskQueue<StarTask, mtGC>           OopStarTaskQueue;
 562 typedef GenericTaskQueueSet<OopStarTaskQueue, mtGC> OopStarTaskQueueSet;
 563 
 564 typedef OverflowTaskQueue<size_t, mtGC>             RegionTaskQueue;
 565 typedef GenericTaskQueueSet<RegionTaskQueue, mtGC>  RegionTaskQueueSet;
 566 
 567 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP