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.
   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 "memory/padded.hpp"
  30 #include "oops/oopsHierarchy.hpp"
  31 #include "utilities/ostream.hpp"
  32 #include "utilities/stack.hpp"
  33 
  34 // Simple TaskQueue stats that are collected by default in debug builds.
  35 
  36 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
  37 #define TASKQUEUE_STATS 1
  38 #elif !defined(TASKQUEUE_STATS)
  39 #define TASKQUEUE_STATS 0
  40 #endif
  41 
  42 #if TASKQUEUE_STATS
  43 #define TASKQUEUE_STATS_ONLY(code) code
  44 #else
  45 #define TASKQUEUE_STATS_ONLY(code)
  46 #endif // TASKQUEUE_STATS
  47 
  48 #if TASKQUEUE_STATS
  49 class TaskQueueStats {
  50 public:
  51   enum StatId {
  52     push,             // number of taskqueue pushes
  53     pop,              // number of taskqueue pops
  54     pop_slow,         // subset of taskqueue pops that were done slow-path
  55     steal_attempt,    // number of taskqueue steal attempts
  56     steal,            // number of taskqueue steals
  57     overflow,         // number of overflow pushes
  58     overflow_max_len, // max length of overflow stack
  59     last_stat_id
  60   };
  61 
  62 public:
  63   inline TaskQueueStats()       { reset(); }
  64 
  65   inline void record_push()     { ++_stats[push]; }
  66   inline void record_pop()      { ++_stats[pop]; }
  67   inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
  68   inline void record_steal(bool success);
  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_steal(bool success) {
  92   ++_stats[steal_attempt];
  93   if (success) ++_stats[steal];
  94 }
  95 
  96 void TaskQueueStats::record_overflow(size_t new_len) {
  97   ++_stats[overflow];
  98   if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
  99 }
 100 
 101 void TaskQueueStats::reset() {
 102   memset(_stats, 0, sizeof(_stats));
 103 }
 104 #endif // TASKQUEUE_STATS
 105 
 106 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
 107 
 108 template <unsigned int N, MEMFLAGS F>
 109 class TaskQueueSuper: public CHeapObj<F> {
 110 protected:
 111   // Internal type for indexing the queue; also used for the tag.
 112   typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
 113 
 114   // The first free element after the last one pushed (mod N).
 115   volatile uint _bottom;
 116 
 117   enum { MOD_N_MASK = N - 1 };
 118 
 119   class Age {
 120   public:
 121     Age(size_t data = 0)         { _data = data; }
 122     Age(const Age& age)          { _data = age._data; }
 123     Age(idx_t top, idx_t tag)    { _fields._top = top; _fields._tag = tag; }
 124 
 125     Age   get()        const volatile { return _data; }
 126     void  set(Age age) volatile       { _data = age._data; }
 127 
 128     idx_t top()        const volatile { return _fields._top; }
 129     idx_t tag()        const volatile { return _fields._tag; }
 130 
 131     // Increment top; if it wraps, increment tag also.
 132     void increment() {
 133       _fields._top = increment_index(_fields._top);
 134       if (_fields._top == 0) ++_fields._tag;
 135     }
 136 
 137     Age cmpxchg(const Age new_age, const Age old_age) volatile;
 138 
 139     bool operator ==(const Age& other) const { return _data == other._data; }
 140 
 141   private:
 142     struct fields {
 143       idx_t _top;
 144       idx_t _tag;
 145     };
 146     union {
 147       size_t _data;
 148       fields _fields;
 149     };
 150   };
 151 
 152   volatile Age _age;
 153 
 154   // These both operate mod N.
 155   static uint increment_index(uint ind) {
 156     return (ind + 1) & MOD_N_MASK;
 157   }
 158   static uint decrement_index(uint ind) {
 159     return (ind - 1) & MOD_N_MASK;
 160   }
 161 
 162   // Returns a number in the range [0..N).  If the result is "N-1", it should be
 163   // interpreted as 0.
 164   uint dirty_size(uint bot, uint top) const {
 165     return (bot - top) & MOD_N_MASK;
 166   }
 167 
 168   // Returns the size corresponding to the given "bot" and "top".
 169   uint size(uint bot, uint top) const {
 170     uint sz = dirty_size(bot, top);
 171     // Has the queue "wrapped", so that bottom is less than top?  There's a
 172     // complicated special case here.  A pair of threads could perform pop_local
 173     // and pop_global operations concurrently, starting from a state in which
 174     // _bottom == _top+1.  The pop_local could succeed in decrementing _bottom,
 175     // and the pop_global in incrementing _top (in which case the pop_global
 176     // will be awarded the contested queue element.)  The resulting state must
 177     // be interpreted as an empty queue.  (We only need to worry about one such
 178     // event: only the queue owner performs pop_local's, and several concurrent
 179     // threads attempting to perform the pop_global will all perform the same
 180     // CAS, and only one can succeed.)  Any stealing thread that reads after
 181     // either the increment or decrement will see an empty queue, and will not
 182     // join the competitors.  The "sz == -1 || sz == N-1" state will not be
 183     // modified by concurrent queues, so the owner thread can reset the state to
 184     // _bottom == top so subsequent pushes will be performed normally.
 185     return (sz == N - 1) ? 0 : sz;
 186   }
 187 
 188 public:
 189   TaskQueueSuper() : _bottom(0), _age() {}
 190 
 191   // Return true if the TaskQueue contains/does not contain any tasks.
 192   bool peek()     const { return _bottom != _age.top(); }
 193   bool is_empty() const { return size() == 0; }
 194 
 195   // Return an estimate of the number of elements in the queue.
 196   // The "careful" version admits the possibility of pop_local/pop_global
 197   // races.
 198   uint size() const {
 199     return size(_bottom, _age.top());
 200   }
 201 
 202   uint dirty_size() const {
 203     return dirty_size(_bottom, _age.top());
 204   }
 205 
 206   void set_empty() {
 207     _bottom = 0;
 208     _age.set(0);
 209   }
 210 
 211   // Maximum number of elements allowed in the queue.  This is two less
 212   // than the actual queue size, for somewhat complicated reasons.
 213   uint max_elems() const { return N - 2; }
 214 
 215   // Total size of queue.
 216   static const uint total_size() { return N; }
 217 
 218   TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
 219 };
 220 
 221 //
 222 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
 223 // ended-queue (deque), intended for use in work stealing. Queue operations
 224 // are non-blocking.
 225 //
 226 // A queue owner thread performs push() and pop_local() operations on one end
 227 // of the queue, while other threads may steal work using the pop_global()
 228 // method.
 229 //
 230 // The main difference to the original algorithm is that this
 231 // implementation allows wrap-around at the end of its allocated
 232 // storage, which is an array.
 233 //
 234 // The original paper is:
 235 //
 236 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
 237 // Thread scheduling for multiprogrammed multiprocessors.
 238 // Theory of Computing Systems 34, 2 (2001), 115-144.
 239 //
 240 // The following paper provides an correctness proof and an
 241 // implementation for weakly ordered memory models including (pseudo-)
 242 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
 243 // similar to ABP, with the main difference that it allows resizing of the
 244 // underlying storage:
 245 //
 246 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
 247 // Correct and efficient work-stealing for weak memory models
 248 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
 249 // practice of parallel programming (PPoPP 2013), 69-80
 250 //
 251 
 252 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 253 class GenericTaskQueue: public TaskQueueSuper<N, F> {
 254 protected:
 255   typedef typename TaskQueueSuper<N, F>::Age Age;
 256   typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
 257 
 258   using TaskQueueSuper<N, F>::_bottom;
 259   using TaskQueueSuper<N, F>::_age;
 260   using TaskQueueSuper<N, F>::increment_index;
 261   using TaskQueueSuper<N, F>::decrement_index;
 262   using TaskQueueSuper<N, F>::dirty_size;
 263 
 264 public:
 265   using TaskQueueSuper<N, F>::max_elems;
 266   using TaskQueueSuper<N, F>::size;
 267 
 268 #if  TASKQUEUE_STATS
 269   using TaskQueueSuper<N, F>::stats;
 270 #endif
 271 
 272 private:
 273   // Slow paths for push, pop_local.  (pop_global has no fast path.)
 274   bool push_slow(E t, uint dirty_n_elems);
 275   bool pop_local_slow(uint localBot, Age oldAge);
 276 
 277 public:
 278   typedef E element_type;
 279 
 280   // Initializes the queue to empty.
 281   GenericTaskQueue();
 282 
 283   void initialize();
 284 
 285   // Push the task "t" on the queue.  Returns "false" iff the queue is full.
 286   inline bool push(E t);
 287 
 288   // Attempts to claim a task from the "local" end of the queue (the most
 289   // recently pushed) as long as the number of entries exceeds the threshold.
 290   // If successful, returns true and sets t to the task; otherwise, returns false
 291   // (the queue is empty or the number of elements below the threshold).
 292   inline bool pop_local(volatile E& t, uint threshold = 0);
 293 
 294   // Like pop_local(), but uses the "global" end of the queue (the least
 295   // recently pushed).
 296   bool pop_global(volatile E& t);
 297 
 298   // Delete any resource associated with the queue.
 299   ~GenericTaskQueue();
 300 
 301   // Apply fn to each element in the task queue.  The queue must not
 302   // be modified while iterating.
 303   template<typename Fn> void iterate(Fn fn);
 304 
 305 private:
 306   // Element array.
 307   volatile E* _elems;
 308 };
 309 
 310 template<class E, MEMFLAGS F, unsigned int N>
 311 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
 312   assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
 313 }
 314 
 315 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
 316 // elements that do not fit in the TaskQueue.
 317 //
 318 // This class hides two methods from super classes:
 319 //
 320 // push() - push onto the task queue or, if that fails, onto the overflow stack
 321 // is_empty() - return true if both the TaskQueue and overflow stack are empty
 322 //
 323 // Note that size() is not hidden--it returns the number of elements in the
 324 // TaskQueue, and does not include the size of the overflow stack.  This
 325 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
 326 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
 327 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
 328 {
 329 public:
 330   typedef Stack<E, F>               overflow_t;
 331   typedef GenericTaskQueue<E, F, N> taskqueue_t;
 332 
 333   TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
 334 
 335   // Push task t onto the queue or onto the overflow stack.  Return true.
 336   inline bool push(E t);
 337   // Try to push task t onto the queue only. Returns true if successful, false otherwise.
 338   inline bool try_push_to_taskqueue(E t);
 339 
 340   // Attempt to pop from the overflow stack; return true if anything was popped.
 341   inline bool pop_overflow(E& t);
 342 
 343   inline overflow_t* overflow_stack() { return &_overflow_stack; }
 344 
 345   inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
 346   inline bool overflow_empty()  const { return _overflow_stack.is_empty(); }
 347   inline bool is_empty()        const {
 348     return taskqueue_empty() && overflow_empty();
 349   }
 350 
 351 private:
 352   overflow_t _overflow_stack;
 353 };
 354 
 355 class TaskQueueSetSuper {
 356 protected:
 357   static int randomParkAndMiller(int* seed0);
 358 public:
 359   // Returns "true" if some TaskQueue in the set contains a task.
 360   virtual bool peek() = 0;

 361 };
 362 
 363 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
 364 };
 365 
 366 template<class T, MEMFLAGS F>
 367 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
 368 private:
 369   uint _n;
 370   T** _queues;
 371 
 372 public:
 373   typedef typename T::element_type E;
 374 
 375   GenericTaskQueueSet(int n);
 376   ~GenericTaskQueueSet();
 377 
 378   bool steal_best_of_2(uint queue_num, int* seed, E& t);
 379 
 380   void register_queue(uint i, T* q);
 381 
 382   T* queue(uint n);
 383 
 384   // The thread with queue number "queue_num" (and whose random number seed is
 385   // at "seed") is trying to steal a task from some other queue.  (It may try
 386   // several queues, according to some configuration parameter.)  If some steal
 387   // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
 388   // false.
 389   bool steal(uint queue_num, int* seed, E& t);
 390 
 391   bool peek();

 392 
 393   uint size() const { return _n; }
 394 };
 395 
 396 template<class T, MEMFLAGS F> void
 397 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
 398   assert(i < _n, "index out of range.");
 399   _queues[i] = q;
 400 }
 401 
 402 template<class T, MEMFLAGS F> T*
 403 GenericTaskQueueSet<T, F>::queue(uint i) {
 404   return _queues[i];
 405 }
 406 
 407 template<class T, MEMFLAGS F>
 408 bool GenericTaskQueueSet<T, F>::peek() {
 409   // Try all the queues.
 410   for (uint j = 0; j < _n; j++) {
 411     if (_queues[j]->peek())
 412       return true;
 413   }
 414   return false;
 415 }
 416 










 417 // When to terminate from the termination protocol.
 418 class TerminatorTerminator: public CHeapObj<mtInternal> {
 419 public:
 420   virtual bool should_exit_termination() = 0;
 421 };
 422 
 423 // A class to aid in the termination of a set of parallel tasks using
 424 // TaskQueueSet's for work stealing.
 425 
 426 #undef TRACESPINNING
 427 
 428 class ParallelTaskTerminator: public StackObj {
 429 private:
 430   uint _n_threads;
 431   TaskQueueSetSuper* _queue_set;
 432 
 433   DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);
 434   volatile uint _offered_termination;
 435   DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile uint));
 436 
 437 #ifdef TRACESPINNING
 438   static uint _total_yields;
 439   static uint _total_spins;
 440   static uint _total_peeks;
 441 #endif
 442 
 443   bool peek_in_queue_set();
 444 protected:
 445   virtual void yield();
 446   void sleep(uint millis);
 447 
 448 public:
 449 
 450   // "n_threads" is the number of threads to be terminated.  "queue_set" is a
 451   // queue sets of work queues of other threads.
 452   ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);
 453 
 454   // The current thread has no work, and is ready to terminate if everyone
 455   // else is.  If returns "true", all threads are terminated.  If returns
 456   // "false", available work has been observed in one of the task queues,
 457   // so the global task is not complete.
 458   bool offer_termination() {
 459     return offer_termination(NULL);
 460   }
 461 
 462   // As above, but it also terminates if the should_exit_termination()
 463   // method of the terminator parameter returns true. If terminator is
 464   // NULL, then it is ignored.
 465   bool offer_termination(TerminatorTerminator* terminator);
 466 
 467   // Reset the terminator, so that it may be reused again.
 468   // The caller is responsible for ensuring that this is done
 469   // in an MT-safe manner, once the previous round of use of
 470   // the terminator is finished.
 471   void reset_for_reuse();
 472   // Same as above but the number of parallel threads is set to the
 473   // given number.
 474   void reset_for_reuse(uint n_threads);
 475 
 476 #ifdef TRACESPINNING
 477   static uint total_yields() { return _total_yields; }
 478   static uint total_spins() { return _total_spins; }
 479   static uint total_peeks() { return _total_peeks; }
 480   static void print_termination_counts();
 481 #endif
 482 };
 483 
 484 typedef GenericTaskQueue<oop, mtGC>             OopTaskQueue;
 485 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
 486 
 487 #ifdef _MSC_VER
 488 #pragma warning(push)
 489 // warning C4522: multiple assignment operators specified
 490 #pragma warning(disable:4522)
 491 #endif
 492 
 493 // This is a container class for either an oop* or a narrowOop*.
 494 // Both are pushed onto a task queue and the consumer will test is_narrow()
 495 // to determine which should be processed.
 496 class StarTask {
 497   void*  _holder;        // either union oop* or narrowOop*
 498 
 499   enum { COMPRESSED_OOP_MASK = 1 };
 500 
 501  public:
 502   StarTask(narrowOop* p) {
 503     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 504     _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
 505   }
 506   StarTask(oop* p)       {
 507     assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
 508     _holder = (void*)p;
 509   }
 510   StarTask()             { _holder = NULL; }
 511   operator oop*()        { return (oop*)_holder; }
 512   operator narrowOop*()  {
 513     return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
 514   }
 515 
 516   StarTask& operator=(const StarTask& t) {
 517     _holder = t._holder;
 518     return *this;
 519   }
 520   volatile StarTask& operator=(const volatile StarTask& t) volatile {
 521     _holder = t._holder;
 522     return *this;
 523   }
 524 
 525   bool is_narrow() const {
 526     return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
 527   }
 528 };
 529 
 530 class ObjArrayTask
 531 {
 532 public:
 533   ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
 534   ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
 535     assert(idx <= size_t(max_jint), "too big");
 536   }
 537   ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
 538 
 539   ObjArrayTask& operator =(const ObjArrayTask& t) {
 540     _obj = t._obj;
 541     _index = t._index;
 542     return *this;
 543   }
 544   volatile ObjArrayTask&
 545   operator =(const volatile ObjArrayTask& t) volatile {
 546     (void)const_cast<oop&>(_obj = t._obj);
 547     _index = t._index;
 548     return *this;
 549   }
 550 
 551   inline oop obj()   const { return _obj; }
 552   inline int index() const { return _index; }
 553 
 554   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 555 
 556 private:
 557   oop _obj;
 558   int _index;
 559 };
 560 
 561 #ifdef _MSC_VER
 562 #pragma warning(pop)
 563 #endif
 564 
 565 typedef OverflowTaskQueue<StarTask, mtGC>           OopStarTaskQueue;
 566 typedef GenericTaskQueueSet<OopStarTaskQueue, mtGC> OopStarTaskQueueSet;
 567 
 568 typedef OverflowTaskQueue<size_t, mtGC>             RegionTaskQueue;
 569 typedef GenericTaskQueueSet<RegionTaskQueue, mtGC>  RegionTaskQueueSet;
 570 
 571 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP
--- EOF ---