--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/utilities/taskqueue.hpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,525 @@
+/*
+ * 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;
+
+typedef oop* StarTask;
+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