1 /*

     2  * Copyright (c) 2001, 2017, 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, mtGC>           OopStarTaskQueue;

   558 typedef GenericTaskQueueSet<OopStarTaskQueue, mtGC> OopStarTaskQueueSet;

   559 

   560 typedef OverflowTaskQueue<size_t, mtGC>             RegionTaskQueue;

   561 typedef GenericTaskQueueSet<RegionTaskQueue, mtGC>  RegionTaskQueueSet;

   562 

   563 #endif // SHARE_VM_GC_SHARED_TASKQUEUE_HPP