Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 2001-2006 Sun Microsystems, Inc.  All Rights Reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  *

  */

 class TaskQueueSuper: public CHeapObj {

 protected:

   // The first free element after the last one pushed (mod _n).

   // (For now we'll assume only 32-bit CAS).

   volatile juint _bottom;

   // log2 of the size of the queue.

   enum SomeProtectedConstants {

     Log_n = 14

   };

   // Size of the queue.

   juint n() { return (1 << Log_n); }

   // For computing "x mod n" efficiently.

   juint n_mod_mask() { return n() - 1; }

   struct Age {

     jushort _top;

     jushort _tag;

     jushort tag() const { return _tag; }

     jushort top() const { return _top; }

     Age() { _tag = 0; _top = 0; }

     friend bool operator ==(const Age& a1, const Age& a2) {

       return a1.tag() == a2.tag() && a1.top() == a2.top();

     }

   };

   Age _age;

   // These make sure we do single atomic reads and writes.

   Age get_age() {

     jint res = *(volatile jint*)(&_age);

     return *(Age*)(&res);

   }

   void set_age(Age a) {

     *(volatile jint*)(&_age) = *(int*)(&a);

   }

   jushort get_top() {

     return get_age().top();

   }

   // These both operate mod _n.

   juint increment_index(juint ind) {

     return (ind + 1) & n_mod_mask();

   }

   juint decrement_index(juint ind) {

     return (ind - 1) & n_mod_mask();

   }

   // Returns a number in the range [0.._n).  If the result is "n-1", it

   // should be interpreted as 0.

   juint dirty_size(juint bot, juint top) {

     return ((jint)bot - (jint)top) & n_mod_mask();

   }

   // Returns the size corresponding to the given "bot" and "top".

   juint size(juint bot, juint top) {

     juint sz = dirty_size(bot, top);

     // Has the queue "wrapped", so that bottom is less than top?

     // There's a complicated special case here.  A pair of threads could

     // perform pop_local and pop_global operations concurrently, starting

     // from a state in which _bottom == _top+1.  The pop_local could

     // succeed in decrementing _bottom, and the pop_global in incrementing

     // _top (in which case the pop_global will be awarded the contested

     // queue element.)  The resulting state must be interpreted as an empty

     // queue.  (We only need to worry about one such event: only the queue

     // owner performs pop_local's, and several concurrent threads

     // attempting to perform the pop_global will all perform the same CAS,

     // and only one can succeed.  Any stealing thread that reads after

     // either the increment or decrement will seen an empty queue, and will

     // not join the competitors.  The "sz == -1 || sz == _n-1" state will

     // not be modified  by concurrent queues, so the owner thread can reset

     // the state to _bottom == top so subsequent pushes will be performed

     // normally.

     if (sz == (n()-1)) return 0;

     else return sz;

   }

 public:

   TaskQueueSuper() : _bottom(0), _age() {}

   // Return "true" if the TaskQueue contains any tasks.

   bool peek();

   // Return an estimate of the number of elements in the queue.

   // The "careful" version admits the possibility of pop_local/pop_global

   // races.

   juint size() {

     return size(_bottom, get_top());

   }

   juint dirty_size() {

     return dirty_size(_bottom, get_top());

   }

   // Maximum number of elements allowed in the queue.  This is two less

   // than the actual queue size, for somewhat complicated reasons.

   juint max_elems() { return n() - 2; }

 };

 template<class E> class GenericTaskQueue: public TaskQueueSuper {

 private:

   // Slow paths for push, pop_local.  (pop_global has no fast path.)

   bool push_slow(E t, juint dirty_n_elems);

   bool pop_local_slow(juint localBot, Age oldAge);

 public:

   // Initializes the queue to empty.

   GenericTaskQueue();

   void initialize();

   // Push the task "t" on the queue.  Returns "false" iff the queue is

   // full.

   inline bool push(E t);

   // If succeeds in claiming a task (from the 'local' end, that is, the

   // most recently pushed task), returns "true" and sets "t" to that task.

   // Otherwise, the queue is empty and returns false.

   inline bool pop_local(E& t);

   // If succeeds in claiming a task (from the 'global' end, that is, the

   // least recently pushed task), returns "true" and sets "t" to that task.

   // Otherwise, the queue is empty and returns false.

   bool pop_global(E& t);

   // Delete any resource associated with the queue.

   ~GenericTaskQueue();

 private:

   // Element array.

   volatile E* _elems;

 };

 template<class E>

 GenericTaskQueue<E>::GenericTaskQueue():TaskQueueSuper() {

   assert(sizeof(Age) == sizeof(jint), "Depends on this.");

 }

 template<class E>

 void GenericTaskQueue<E>::initialize() {

   _elems = NEW_C_HEAP_ARRAY(E, n());

   guarantee(_elems != NULL, "Allocation failed.");

 }

 template<class E>

 bool GenericTaskQueue<E>::push_slow(E t, juint dirty_n_elems) {

   if (dirty_n_elems == n() - 1) {

     // Actually means 0, so do the push.

     juint localBot = _bottom;

     _elems[localBot] = t;

     _bottom = increment_index(localBot);

     return true;

   } else

     return false;

 }

 template<class E>

 bool GenericTaskQueue<E>::

 pop_local_slow(juint localBot, Age oldAge) {

   // This queue was observed to contain exactly one element; either this

   // thread will claim it, or a competing "pop_global".  In either case,

   // the queue will be logically empty afterwards.  Create a new Age value

   // that represents the empty queue for the given value of "_bottom".  (We

   // must also increment "tag" because of the case where "bottom == 1",

   // "top == 0".  A pop_global could read the queue element in that case,

   // then have the owner thread do a pop followed by another push.  Without

   // the incrementing of "tag", the pop_global's CAS could succeed,

   // allowing it to believe it has claimed the stale element.)

   Age newAge;

   newAge._top = localBot;

   newAge._tag = oldAge.tag() + 1;

   // Perhaps a competing pop_global has already incremented "top", in which

   // case it wins the element.

   if (localBot == oldAge.top()) {

     Age tempAge;

     // No competing pop_global has yet incremented "top"; we'll try to

     // install new_age, thus claiming the element.

     assert(sizeof(Age) == sizeof(jint) && sizeof(jint) == sizeof(juint),

            "Assumption about CAS unit.");

     *(jint*)&tempAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge);

     if (tempAge == oldAge) {

       // We win.

       assert(dirty_size(localBot, get_top()) != n() - 1,

              "Shouldn't be possible...");

       return true;

     }

   }

   // We fail; a completing pop_global gets the element.  But the queue is

   // empty (and top is greater than bottom.)  Fix this representation of

   // the empty queue to become the canonical one.

   set_age(newAge);

   assert(dirty_size(localBot, get_top()) != n() - 1,

          "Shouldn't be possible...");

   return false;

 }

 template<class E>

 bool GenericTaskQueue<E>::pop_global(E& t) {

   Age newAge;

   Age oldAge = get_age();

   juint localBot = _bottom;

   juint n_elems = size(localBot, oldAge.top());

   if (n_elems == 0) {

     return false;

   }

   t = _elems[oldAge.top()];

   newAge = oldAge;

   newAge._top = increment_index(newAge.top());

   if ( newAge._top == 0 ) newAge._tag++;

   Age resAge;

   *(jint*)&resAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge);

   // Note that using "_bottom" here might fail, since a pop_local might

   // have decremented it.

   assert(dirty_size(localBot, newAge._top) != n() - 1,

          "Shouldn't be possible...");

   return (resAge == oldAge);

 }

 template<class E>

 GenericTaskQueue<E>::~GenericTaskQueue() {

   FREE_C_HEAP_ARRAY(E, _elems);

 }

 // Inherits the typedef of "Task" from above.

 class TaskQueueSetSuper: public CHeapObj {

 protected:

   static int randomParkAndMiller(int* seed0);

 public:

   // Returns "true" if some TaskQueue in the set contains a task.

   virtual bool peek() = 0;

 };

 template<class E> class GenericTaskQueueSet: public TaskQueueSetSuper {

 private:

   int _n;

   GenericTaskQueue<E>** _queues;

 public:

   GenericTaskQueueSet(int n) : _n(n) {

     typedef GenericTaskQueue<E>* GenericTaskQueuePtr;

     _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n);

     guarantee(_queues != NULL, "Allocation failure.");

     for (int i = 0; i < n; i++) {

       _queues[i] = NULL;

     }

   }

   bool steal_1_random(int queue_num, int* seed, E& t);

   bool steal_best_of_2(int queue_num, int* seed, E& t);

   bool steal_best_of_all(int queue_num, int* seed, E& t);

   void register_queue(int i, GenericTaskQueue<E>* q);

   GenericTaskQueue<E>* queue(int n);

   // The thread with queue number "queue_num" (and whose random number seed

   // is at "seed") is trying to steal a task from some other queue.  (It

   // may try several queues, according to some configuration parameter.)

   // If some steal succeeds, returns "true" and sets "t" the stolen task,

   // otherwise returns false.

   bool steal(int queue_num, int* seed, E& t);

   bool peek();

 };

 template<class E>

 void GenericTaskQueueSet<E>::register_queue(int i, GenericTaskQueue<E>* q) {

   assert(0 <= i && i < _n, "index out of range.");

   _queues[i] = q;

 }

 template<class E>

 GenericTaskQueue<E>* GenericTaskQueueSet<E>::queue(int i) {

   return _queues[i];

 }

 template<class E>

 bool GenericTaskQueueSet<E>::steal(int queue_num, int* seed, E& t) {

   for (int i = 0; i < 2 * _n; i++)

     if (steal_best_of_2(queue_num, seed, t))

       return true;

   return false;

 }

 template<class E>

 bool GenericTaskQueueSet<E>::steal_best_of_all(int queue_num, int* seed, E& t) {

   if (_n > 2) {

     int best_k;

     jint best_sz = 0;

     for (int k = 0; k < _n; k++) {

       if (k == queue_num) continue;

       jint sz = _queues[k]->size();

       if (sz > best_sz) {

         best_sz = sz;

         best_k = k;

       }

     }

     return best_sz > 0 && _queues[best_k]->pop_global(t);

   } else if (_n == 2) {

     // Just try the other one.

     int k = (queue_num + 1) % 2;

     return _queues[k]->pop_global(t);

   } else {

     assert(_n == 1, "can't be zero.");

     return false;

   }

 }

 template<class E>

 bool GenericTaskQueueSet<E>::steal_1_random(int queue_num, int* seed, E& t) {

   if (_n > 2) {

     int k = queue_num;

     while (k == queue_num) k = randomParkAndMiller(seed) % _n;

     return _queues[2]->pop_global(t);

   } else if (_n == 2) {

     // Just try the other one.

     int k = (queue_num + 1) % 2;

     return _queues[k]->pop_global(t);

   } else {

     assert(_n == 1, "can't be zero.");

     return false;

   }

 }

 template<class E>

 bool GenericTaskQueueSet<E>::steal_best_of_2(int queue_num, int* seed, E& t) {

   if (_n > 2) {

     int k1 = queue_num;

     while (k1 == queue_num) k1 = randomParkAndMiller(seed) % _n;

     int k2 = queue_num;

     while (k2 == queue_num || k2 == k1) k2 = randomParkAndMiller(seed) % _n;

     // Sample both and try the larger.

     juint sz1 = _queues[k1]->size();

     juint sz2 = _queues[k2]->size();

     if (sz2 > sz1) return _queues[k2]->pop_global(t);

     else return _queues[k1]->pop_global(t);

   } else if (_n == 2) {

     // Just try the other one.

     int k = (queue_num + 1) % 2;

     return _queues[k]->pop_global(t);

   } else {

     assert(_n == 1, "can't be zero.");

     return false;

   }

 }

 template<class E>

 bool GenericTaskQueueSet<E>::peek() {

   // Try all the queues.

   for (int j = 0; j < _n; j++) {

     if (_queues[j]->peek())

       return true;

   }

   return false;

 }

 // A class to aid in the termination of a set of parallel tasks using

 // TaskQueueSet's for work stealing.

 class ParallelTaskTerminator: public StackObj {

 private:

   int _n_threads;

   TaskQueueSetSuper* _queue_set;

   jint _offered_termination;

   bool peek_in_queue_set();

 protected:

   virtual void yield();

   void sleep(uint millis);

 public:

   // "n_threads" is the number of threads to be terminated.  "queue_set" is a

   // queue sets of work queues of other threads.

   ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);

   // The current thread has no work, and is ready to terminate if everyone

   // else is.  If returns "true", all threads are terminated.  If returns

   // "false", available work has been observed in one of the task queues,

   // so the global task is not complete.

   bool offer_termination();

   // Reset the terminator, so that it may be reused again.

   // The caller is responsible for ensuring that this is done

   // in an MT-safe manner, once the previous round of use of

   // the terminator is finished.

   void reset_for_reuse();

 };

 #define SIMPLE_STACK 0

 template<class E> inline bool GenericTaskQueue<E>::push(E t) {

 #if SIMPLE_STACK

   juint localBot = _bottom;

   if (_bottom < max_elems()) {

     _elems[localBot] = t;

     _bottom = localBot + 1;

     return true;

   } else {

     return false;

   }

 #else

   juint localBot = _bottom;

   assert((localBot >= 0) && (localBot < n()), "_bottom out of range.");

   jushort top = get_top();

   juint dirty_n_elems = dirty_size(localBot, top);

   assert((dirty_n_elems >= 0) && (dirty_n_elems < n()),

          "n_elems out of range.");

   if (dirty_n_elems < max_elems()) {

     _elems[localBot] = t;

     _bottom = increment_index(localBot);

     return true;

   } else {

     return push_slow(t, dirty_n_elems);

   }

 #endif

 }

 template<class E> inline bool GenericTaskQueue<E>::pop_local(E& t) {

 #if SIMPLE_STACK

   juint localBot = _bottom;

   assert(localBot > 0, "precondition.");

   localBot--;

   t = _elems[localBot];

   _bottom = localBot;

   return true;

 #else

   juint localBot = _bottom;

   // This value cannot be n-1.  That can only occur as a result of

   // the assignment to bottom in this method.  If it does, this method

   // resets the size( to 0 before the next call (which is sequential,

   // since this is pop_local.)

   juint dirty_n_elems = dirty_size(localBot, get_top());

   assert(dirty_n_elems != n() - 1, "Shouldn't be possible...");

   if (dirty_n_elems == 0) return false;

   localBot = decrement_index(localBot);

   _bottom = localBot;

   // This is necessary to prevent any read below from being reordered

   // before the store just above.

   OrderAccess::fence();

   t = _elems[localBot];

   // This is a second read of "age"; the "size()" above is the first.

   // If there's still at least one element in the queue, based on the

   // "_bottom" and "age" we've read, then there can be no interference with

   // a "pop_global" operation, and we're done.

   juint tp = get_top();

   if (size(localBot, tp) > 0) {

     assert(dirty_size(localBot, tp) != n() - 1,

            "Shouldn't be possible...");

     return true;

   } else {

     // Otherwise, the queue contained exactly one element; we take the slow

     // path.

     return pop_local_slow(localBot, get_age());

   }

 #endif

 }

 typedef oop Task;

 typedef GenericTaskQueue<Task>         OopTaskQueue;

 typedef GenericTaskQueueSet<Task>      OopTaskQueueSet;

 #define COMPRESSED_OOP_MASK  1

 // This is a container class for either an oop* or a narrowOop*.

 // Both are pushed onto a task queue and the consumer will test is_narrow()

 // to determine which should be processed.

 class StarTask {

   void*  _holder;        // either union oop* or narrowOop*

  public:

   StarTask(narrowOop *p) { _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK); }

   StarTask(oop *p)       { _holder = (void*)p; }

   StarTask()             { _holder = NULL; }

   operator oop*()        { return (oop*)_holder; }

   operator narrowOop*()  {

     return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);

   }

   // Operators to preserve const/volatile in assignments required by gcc

   void operator=(const volatile StarTask& t) volatile { _holder = t._holder; }

   bool is_narrow() const {

     return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);

   }

 };

 typedef GenericTaskQueue<StarTask>     OopStarTaskQueue;

 typedef GenericTaskQueueSet<StarTask>  OopStarTaskQueueSet;

 typedef size_t ChunkTask;  // index for chunk

 typedef GenericTaskQueue<ChunkTask>    ChunkTaskQueue;

 typedef GenericTaskQueueSet<ChunkTask> ChunkTaskQueueSet;

 class ChunkTaskQueueWithOverflow: public CHeapObj {

  protected:

   ChunkTaskQueue              _chunk_queue;

   GrowableArray<ChunkTask>*   _overflow_stack;

  public:

   ChunkTaskQueueWithOverflow() : _overflow_stack(NULL) {}

   // Initialize both stealable queue and overflow

   void initialize();

   // Save first to stealable queue and then to overflow

   void save(ChunkTask t);

   // Retrieve first from overflow and then from stealable queue

   bool retrieve(ChunkTask& chunk_index);

   // Retrieve from stealable queue

   bool retrieve_from_stealable_queue(ChunkTask& chunk_index);

   // Retrieve from overflow

   bool retrieve_from_overflow(ChunkTask& chunk_index);

   bool is_empty();

   bool stealable_is_empty();

   bool overflow_is_empty();

   juint stealable_size() { return _chunk_queue.size(); }

   ChunkTaskQueue* task_queue() { return &_chunk_queue; }

 };

 #define USE_ChunkTaskQueueWithOverflow