--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/gc/shared/taskqueue.inline.hpp	Wed May 13 15:16:06 2015 +0200
@@ -0,0 +1,279 @@
+/*
+ * Copyright (c) 2015, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP
+#define SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP
+
+#include "gc/shared/taskqueue.hpp"
+#include "memory/allocation.inline.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/atomic.inline.hpp"
+#include "runtime/orderAccess.inline.hpp"
+#include "utilities/debug.hpp"
+#include "utilities/stack.inline.hpp"
+
+template <class T, MEMFLAGS F>
+inline GenericTaskQueueSet<T, F>::GenericTaskQueueSet(int n) : _n(n) {
+  typedef T* GenericTaskQueuePtr;
+  _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);
+  for (int i = 0; i < n; i++) {
+    _queues[i] = NULL;
+  }
+}
+
+template<class E, MEMFLAGS F, unsigned int N>
+inline void GenericTaskQueue<E, F, N>::initialize() {
+  _elems = _array_allocator.allocate(N);
+}
+
+template<class E, MEMFLAGS F, unsigned int N>
+inline GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
+  FREE_C_HEAP_ARRAY(E, _elems);
+}
+
+template<class E, MEMFLAGS F, unsigned int N>
+bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
+  if (dirty_n_elems == N - 1) {
+    // Actually means 0, so do the push.
+    uint localBot = _bottom;
+    // g++ complains if the volatile result of the assignment is
+    // unused, so we cast the volatile away.  We cannot cast directly
+    // to void, because gcc treats that as not using the result of the
+    // assignment.  However, casting to E& means that we trigger an
+    // unused-value warning.  So, we cast the E& to void.
+    (void)const_cast<E&>(_elems[localBot] = t);
+    OrderAccess::release_store(&_bottom, increment_index(localBot));
+    TASKQUEUE_STATS_ONLY(stats.record_push());
+    return true;
+  }
+  return false;
+}
+
+template<class E, MEMFLAGS F, unsigned int N> inline bool
+GenericTaskQueue<E, F, N>::push(E t) {
+  uint localBot = _bottom;
+  assert(localBot < N, "_bottom out of range.");
+  idx_t top = _age.top();
+  uint dirty_n_elems = dirty_size(localBot, top);
+  assert(dirty_n_elems < N, "n_elems out of range.");
+  if (dirty_n_elems < max_elems()) {
+    // g++ complains if the volatile result of the assignment is
+    // unused, so we cast the volatile away.  We cannot cast directly
+    // to void, because gcc treats that as not using the result of the
+    // assignment.  However, casting to E& means that we trigger an
+    // unused-value warning.  So, we cast the E& to void.
+    (void) const_cast<E&>(_elems[localBot] = t);
+    OrderAccess::release_store(&_bottom, increment_index(localBot));
+    TASKQUEUE_STATS_ONLY(stats.record_push());
+    return true;
+  } else {
+    return push_slow(t, dirty_n_elems);
+  }
+}
+
+template <class E, MEMFLAGS F, unsigned int N>
+inline bool OverflowTaskQueue<E, F, N>::push(E t)
+{
+  if (!taskqueue_t::push(t)) {
+    overflow_stack()->push(t);
+    TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
+  }
+  return true;
+}
+
+// pop_local_slow() is done by the owning thread and is trying to
+// get the last task in the queue.  It will compete with pop_global()
+// that will be used by other threads.  The tag age is incremented
+// whenever the queue goes empty which it will do here if this thread
+// gets the last task or in pop_global() if the queue wraps (top == 0
+// and pop_global() succeeds, see pop_global()).
+template<class E, MEMFLAGS F, unsigned int N>
+bool GenericTaskQueue<E, F, N>::pop_local_slow(uint 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((idx_t)localBot, oldAge.tag() + 1);
+  // Perhaps a competing pop_global has already incremented "top", in which
+  // case it wins the element.
+  if (localBot == oldAge.top()) {
+    // No competing pop_global has yet incremented "top"; we'll try to
+    // install new_age, thus claiming the element.
+    Age tempAge = _age.cmpxchg(newAge, oldAge);
+    if (tempAge == oldAge) {
+      // We win.
+      assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
+      TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
+      return true;
+    }
+  }
+  // We lose; 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.
+  _age.set(newAge);
+  assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
+  return false;
+}
+
+template<class E, MEMFLAGS F, unsigned int N> inline bool
+GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
+  uint 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.)
+  uint dirty_n_elems = dirty_size(localBot, _age.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();
+  // g++ complains if the volatile result of the assignment is
+  // unused, so we cast the volatile away.  We cannot cast directly
+  // to void, because gcc treats that as not using the result of the
+  // assignment.  However, casting to E& means that we trigger an
+  // unused-value warning.  So, we cast the E& to void.
+  (void) const_cast<E&>(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.
+  idx_t tp = _age.top();    // XXX
+  if (size(localBot, tp) > 0) {
+    assert(dirty_size(localBot, tp) != N - 1, "sanity");
+    TASKQUEUE_STATS_ONLY(stats.record_pop());
+    return true;
+  } else {
+    // Otherwise, the queue contained exactly one element; we take the slow
+    // path.
+    return pop_local_slow(localBot, _age.get());
+  }
+}
+
+template <class E, MEMFLAGS F, unsigned int N>
+bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
+{
+  if (overflow_empty()) return false;
+  t = overflow_stack()->pop();
+  return true;
+}
+
+template<class E, MEMFLAGS F, unsigned int N>
+bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
+  Age oldAge = _age.get();
+  // Architectures with weak memory model require a barrier here
+  // to guarantee that bottom is not older than age,
+  // which is crucial for the correctness of the algorithm.
+#if !(defined SPARC || defined IA32 || defined AMD64)
+  OrderAccess::fence();
+#endif
+  uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
+  uint n_elems = size(localBot, oldAge.top());
+  if (n_elems == 0) {
+    return false;
+  }
+
+  // g++ complains if the volatile result of the assignment is
+  // unused, so we cast the volatile away.  We cannot cast directly
+  // to void, because gcc treats that as not using the result of the
+  // assignment.  However, casting to E& means that we trigger an
+  // unused-value warning.  So, we cast the E& to void.
+  (void) const_cast<E&>(t = _elems[oldAge.top()]);
+  Age newAge(oldAge);
+  newAge.increment();
+  Age resAge = _age.cmpxchg(newAge, oldAge);
+
+  // Note that using "_bottom" here might fail, since a pop_local might
+  // have decremented it.
+  assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
+  return resAge == oldAge;
+}
+
+template<class T, MEMFLAGS F> bool
+GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
+  if (_n > 2) {
+    uint k1 = queue_num;
+    while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
+    uint k2 = queue_num;
+    while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
+    // Sample both and try the larger.
+    uint sz1 = _queues[k1]->size();
+    uint 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.
+    uint k = (queue_num + 1) % 2;
+    return _queues[k]->pop_global(t);
+  } else {
+    assert(_n == 1, "can't be zero.");
+    return false;
+  }
+}
+
+template<class T, MEMFLAGS F> bool
+GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
+  for (uint i = 0; i < 2 * _n; i++) {
+    if (steal_best_of_2(queue_num, seed, t)) {
+      TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
+      return true;
+    }
+  }
+  TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
+  return false;
+}
+
+template <unsigned int N, MEMFLAGS F>
+inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile {
+  return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
+                                      (volatile intptr_t *)&_data,
+                                      (intptr_t)old_age._data);
+}
+
+template<class E, MEMFLAGS F, unsigned int N>
+inline void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {
+  // tty->print_cr("START OopTaskQueue::oops_do");
+  uint iters = size();
+  uint index = _bottom;
+  for (uint i = 0; i < iters; ++i) {
+    index = decrement_index(index);
+    // tty->print_cr("  doing entry %d," INTPTR_T " -> " INTPTR_T,
+    //            index, &_elems[index], _elems[index]);
+    E* t = (E*)&_elems[index];      // cast away volatility
+    oop* p = (oop*)t;
+    assert((*t)->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(*t)));
+    f->do_oop(p);
+  }
+  // tty->print_cr("END OopTaskQueue::oops_do");
+}
+
+
+#endif // SHARE_VM_GC_SHARED_TASKQUEUE_INLINE_HPP