/*

 * 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.

 *

 *

 */

template <unsigned int N>

class TaskQueueSuper: public CHeapObj {

protected:

  // Internal type for indexing the queue; also used for the tag.

  typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;

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

  volatile uint _bottom;

  enum { MOD_N_MASK = N - 1 };

  class Age {

  public:

    Age(size_t data = 0)         { _data = data; }

    Age(const Age& age)          { _data = age._data; }

    Age(idx_t top, idx_t tag)    { _fields._top = top; _fields._tag = tag; }

    Age   get()        const volatile { return _data; }

    void  set(Age age) volatile       { _data = age._data; }

    idx_t top()        const volatile { return _fields._top; }

    idx_t tag()        const volatile { return _fields._tag; }

    // Increment top; if it wraps, increment tag also.

    void increment() {

      _fields._top = increment_index(_fields._top);

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

    }

    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);

    }

    bool operator ==(const Age& other) const { return _data == other._data; }

  private:

    struct fields {

      idx_t _top;

      idx_t _tag;

    };

    union {

      size_t _data;

      fields _fields;

    };

  };

  volatile Age _age;

  // These both operate mod N.

  static uint increment_index(uint ind) {

    return (ind + 1) & MOD_N_MASK;

  }

  static uint decrement_index(uint ind) {

    return (ind - 1) & MOD_N_MASK;

  }

  // Returns a number in the range [0..N).  If the result is "N-1", it should be

  // interpreted as 0.

  uint dirty_size(uint bot, uint top) const {

    return (bot - top) & MOD_N_MASK;

  }

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

  uint size(uint bot, uint top) const {

    uint 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 see 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.

    return (sz == N - 1) ? 0 : sz;

  }

public:

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

  // Return true if the TaskQueue contains any tasks.

  bool peek() { return _bottom != _age.top(); }

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

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

  // races.

  uint size() const {

    return size(_bottom, _age.top());

  }

  uint dirty_size() const {

    return dirty_size(_bottom, _age.top());

  }

  void set_empty() {

    _bottom = 0;

    _age.set(0);

  }

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

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

  uint max_elems() const { return N - 2; }

  // Total size of queue.

  static const uint total_size() { return N; }

};

template<class E, unsigned int N = TASKQUEUE_SIZE>

class GenericTaskQueue: public TaskQueueSuper<N> {

protected:

  typedef typename TaskQueueSuper<N>::Age Age;

  typedef typename TaskQueueSuper<N>::idx_t idx_t;

  using TaskQueueSuper<N>::_bottom;

  using TaskQueueSuper<N>::_age;

  using TaskQueueSuper<N>::increment_index;

  using TaskQueueSuper<N>::decrement_index;

  using TaskQueueSuper<N>::dirty_size;

public:

  using TaskQueueSuper<N>::max_elems;

  using TaskQueueSuper<N>::size;

private:

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

  bool push_slow(E t, uint dirty_n_elems);

  bool pop_local_slow(uint localBot, Age oldAge);

public:

  typedef E element_type;

  // 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();

  // apply the closure to all elements in the task queue

  void oops_do(OopClosure* f);

private:

  // Element array.

  volatile E* _elems;

};

template<class E, unsigned int N>

GenericTaskQueue<E, N>::GenericTaskQueue() {

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

}

template<class E, unsigned int N>

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

  _elems = NEW_C_HEAP_ARRAY(E, N);

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

}

template<class E, unsigned int N>

void GenericTaskQueue<E, 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(), "Not an oop or null");

    f->do_oop(p);

  }

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

}

template<class E, unsigned int N>

bool GenericTaskQueue<E, 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.

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

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

    return true;

  }

  return false;

}

template<class E, unsigned int N>

bool GenericTaskQueue<E, 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");

      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, unsigned int N>

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

  Age oldAge = _age.get();

  uint localBot = _bottom;

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

  if (n_elems == 0) {

    return false;

  }

  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 E, unsigned int N>

GenericTaskQueue<E, N>::~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 T>

class GenericTaskQueueSet: public TaskQueueSetSuper {

private:

  uint _n;

  T** _queues;

public:

  typedef typename T::element_type E;

  GenericTaskQueueSet(int n) : _n(n) {

    typedef T* GenericTaskQueuePtr;

    _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n);

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

      _queues[i] = NULL;

    }

  }

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

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

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

  void register_queue(uint i, T* q);

  T* queue(uint 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(uint queue_num, int* seed, E& t);

  bool peek();

};

template<class T> void

GenericTaskQueueSet<T>::register_queue(uint i, T* q) {

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

  _queues[i] = q;

}

template<class T> T*

GenericTaskQueueSet<T>::queue(uint i) {

  return _queues[i];

}

template<class T> bool

GenericTaskQueueSet<T>::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))

      return true;

  return false;

}

template<class T> bool

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

  if (_n > 2) {

    int best_k;

    uint best_sz = 0;

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

      if (k == queue_num) continue;

      uint 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 T> bool

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

  if (_n > 2) {

    uint 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 T> bool

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

  if (_n > 2) {

    uint k1 = queue_num;

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

    uint k2 = queue_num;

    while (k2 == queue_num || k2 == k1) k2 = 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>

bool GenericTaskQueueSet<T>::peek() {

  // Try all the queues.

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

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

      return true;

  }

  return false;

}

// When to terminate from the termination protocol.

class TerminatorTerminator: public CHeapObj {

public:

  virtual bool should_exit_termination() = 0;

};

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

// TaskQueueSet's for work stealing.

#undef TRACESPINNING

class ParallelTaskTerminator: public StackObj {

private:

  int _n_threads;

  TaskQueueSetSuper* _queue_set;

  int _offered_termination;

#ifdef TRACESPINNING

  static uint _total_yields;

  static uint _total_spins;

  static uint _total_peeks;

#endif

  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() {

    return offer_termination(NULL);

  }

  // As above, but it also terminates if the should_exit_termination()

  // method of the terminator parameter returns true. If terminator is

  // NULL, then it is ignored.

  bool offer_termination(TerminatorTerminator* terminator);

  // 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();

#ifdef TRACESPINNING

  static uint total_yields() { return _total_yields; }

  static uint total_spins() { return _total_spins; }

  static uint total_peeks() { return _total_peeks; }

  static void print_termination_counts();

#endif

};

template<class E, unsigned int N> inline bool

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

  uint localBot = _bottom;

  assert((localBot >= 0) && (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.

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

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

    return true;

  } else {

    return push_slow(t, dirty_n_elems);