29 #include "memory/allocation.inline.hpp"

    30 #include "runtime/mutex.hpp"

    31 #include "runtime/orderAccess.inline.hpp"

   318 template<class E, MEMFLAGS F, unsigned int N>

   319 void GenericTaskQueue<E, F, N>::initialize() {

   320   _elems = _array_allocator.allocate(N);

   321 }

   322 

   323 template<class E, MEMFLAGS F, unsigned int N>

   324 void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {

   325   // tty->print_cr("START OopTaskQueue::oops_do");

   326   uint iters = size();

   327   uint index = _bottom;

   328   for (uint i = 0; i < iters; ++i) {

   329     index = decrement_index(index);

   330     // tty->print_cr("  doing entry %d," INTPTR_T " -> " INTPTR_T,

   331     //            index, &_elems[index], _elems[index]);

   332     E* t = (E*)&_elems[index];      // cast away volatility

   333     oop* p = (oop*)t;

   334     assert((*t)->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(*t)));

   335     f->do_oop(p);

   336   }

   337   // tty->print_cr("END OopTaskQueue::oops_do");

   338 }

   339 

   340 template<class E, MEMFLAGS F, unsigned int N>

   341 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {

   342   if (dirty_n_elems == N - 1) {

   343     // Actually means 0, so do the push.

   344     uint localBot = _bottom;

   345     // g++ complains if the volatile result of the assignment is

   346     // unused, so we cast the volatile away.  We cannot cast directly

   347     // to void, because gcc treats that as not using the result of the

   348     // assignment.  However, casting to E& means that we trigger an

   349     // unused-value warning.  So, we cast the E& to void.

   350     (void)const_cast<E&>(_elems[localBot] = t);

   351     OrderAccess::release_store(&_bottom, increment_index(localBot));

   352     TASKQUEUE_STATS_ONLY(stats.record_push());

   353     return true;

   354   }

   355   return false;

   356 }

   357 

   358 // pop_local_slow() is done by the owning thread and is trying to

   359 // get the last task in the queue.  It will compete with pop_global()

   360 // that will be used by other threads.  The tag age is incremented

   361 // whenever the queue goes empty which it will do here if this thread

   362 // gets the last task or in pop_global() if the queue wraps (top == 0

   363 // and pop_global() succeeds, see pop_global()).

   364 template<class E, MEMFLAGS F, unsigned int N>

   365 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {

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

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

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

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

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

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

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

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

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

   375   Age newAge((idx_t)localBot, oldAge.tag() + 1);

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

   377   // case it wins the element.

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

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

   380     // install new_age, thus claiming the element.

   381     Age tempAge = _age.cmpxchg(newAge, oldAge);

   382     if (tempAge == oldAge) {

   383       // We win.

   384       assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");

   385       TASKQUEUE_STATS_ONLY(stats.record_pop_slow());

   386       return true;

   387     }

   388   }

   389   // We lose; a completing pop_global gets the element.  But the queue is empty

   390   // and top is greater than bottom.  Fix this representation of the empty queue

   391   // to become the canonical one.

   392   _age.set(newAge);

   393   assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");

   394   return false;

   395 }

   396 

   397 template<class E, MEMFLAGS F, unsigned int N>

   398 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {

   399   Age oldAge = _age.get();

   400   // Architectures with weak memory model require a barrier here

   401   // to guarantee that bottom is not older than age,

   402   // which is crucial for the correctness of the algorithm.

   403 #if !(defined SPARC || defined IA32 || defined AMD64)

   404   OrderAccess::fence();

   405 #endif

   406   uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);

   407   uint n_elems = size(localBot, oldAge.top());

   408   if (n_elems == 0) {

   409     return false;

   410   }

   411 

   412   // g++ complains if the volatile result of the assignment is

   413   // unused, so we cast the volatile away.  We cannot cast directly

   414   // to void, because gcc treats that as not using the result of the

   415   // assignment.  However, casting to E& means that we trigger an

   416   // unused-value warning.  So, we cast the E& to void.

   417   (void) const_cast<E&>(t = _elems[oldAge.top()]);

   418   Age newAge(oldAge);

   419   newAge.increment();

   420   Age resAge = _age.cmpxchg(newAge, oldAge);

   421 

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

   423   // have decremented it.

   424   assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");

   425   return resAge == oldAge;

   426 }

   427 

   428 template<class E, MEMFLAGS F, unsigned int N>

   429 GenericTaskQueue<E, F, N>::~GenericTaskQueue() {

   430   FREE_C_HEAP_ARRAY(E, _elems);

   431 }

   432 

   471 template <class E, MEMFLAGS F, unsigned int N>

   472 bool OverflowTaskQueue<E, F, N>::push(E t)

   473 {

   474   if (!taskqueue_t::push(t)) {

   475     overflow_stack()->push(t);

   476     TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));

   477   }

   478   return true;

   479 }

   480 

   481 template <class E, MEMFLAGS F, unsigned int N>

   482 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)

   483 {

   484   if (overflow_empty()) return false;

   485   t = overflow_stack()->pop();

   486   return true;

   487 }

   488 

   542 }

   543 

   544 template<class T, MEMFLAGS F> bool

   545 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {

   546   for (uint i = 0; i < 2 * _n; i++) {

   547     if (steal_best_of_2(queue_num, seed, t)) {

   548       TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));

   549       return true;

   550     }

   551   }

   552   TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));

   553   return false;

   554 }

   555 

   556 template<class T, MEMFLAGS F> bool

   557 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {

   558   if (_n > 2) {

   559     uint k1 = queue_num;

   560     while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;

   561     uint k2 = queue_num;

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

   563     // Sample both and try the larger.

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

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

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

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

   568   } else if (_n == 2) {

   569     // Just try the other one.

   570     uint k = (queue_num + 1) % 2;

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

   572   } else {

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

   574     return false;

   575   }

   652 template<class E, MEMFLAGS F, unsigned int N> inline bool

   653 GenericTaskQueue<E, F, N>::push(E t) {

   654   uint localBot = _bottom;

   655   assert(localBot < N, "_bottom out of range.");

   656   idx_t top = _age.top();

   657   uint dirty_n_elems = dirty_size(localBot, top);

   658   assert(dirty_n_elems < N, "n_elems out of range.");

   659   if (dirty_n_elems < max_elems()) {

   660     // g++ complains if the volatile result of the assignment is

   661     // unused, so we cast the volatile away.  We cannot cast directly

   662     // to void, because gcc treats that as not using the result of the

   663     // assignment.  However, casting to E& means that we trigger an

   664     // unused-value warning.  So, we cast the E& to void.

   665     (void) const_cast<E&>(_elems[localBot] = t);

   666     OrderAccess::release_store(&_bottom, increment_index(localBot));

   667     TASKQUEUE_STATS_ONLY(stats.record_push());

   668     return true;

   669   } else {

   670     return push_slow(t, dirty_n_elems);

   671   }

   672 }

   673 

   674 template<class E, MEMFLAGS F, unsigned int N> inline bool

   675 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {

   676   uint localBot = _bottom;

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

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

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

   680   // since this is pop_local.)

   681   uint dirty_n_elems = dirty_size(localBot, _age.top());

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

   683   if (dirty_n_elems == 0) return false;

   684   localBot = decrement_index(localBot);

   685   _bottom = localBot;

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

   687   // before the store just above.

   688   OrderAccess::fence();

   689   // g++ complains if the volatile result of the assignment is

   690   // unused, so we cast the volatile away.  We cannot cast directly

   691   // to void, because gcc treats that as not using the result of the

   692   // assignment.  However, casting to E& means that we trigger an

   693   // unused-value warning.  So, we cast the E& to void.

   694   (void) const_cast<E&>(t = _elems[localBot]);

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

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

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

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

   699   idx_t tp = _age.top();    // XXX

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

   701     assert(dirty_size(localBot, tp) != N - 1, "sanity");

   702     TASKQUEUE_STATS_ONLY(stats.record_pop());

   703     return true;

   704   } else {

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

   706     // path.

   707     return pop_local_slow(localBot, _age.get());

   708   }

   709 }

   710