/*

 * Copyright (c) 2015, 2019, 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_GC_SHARED_TASKQUEUE_INLINE_HPP

#define SHARE_GC_SHARED_TASKQUEUE_INLINE_HPP

#include "gc/shared/taskqueue.hpp"

#include "memory/allocation.inline.hpp"

#include "oops/oop.inline.hpp"

#include "runtime/atomic.hpp"

#include "runtime/orderAccess.hpp"

#include "utilities/debug.hpp"

#include "utilities/stack.inline.hpp"

template <class T, MEMFLAGS F>

inline GenericTaskQueueSet<T, F>::GenericTaskQueueSet(uint n) : _n(n) {

  typedef T* GenericTaskQueuePtr;

  _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);

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

    _queues[i] = NULL;

  }

}

template <class T, MEMFLAGS F>

inline GenericTaskQueueSet<T, F>::~GenericTaskQueueSet() {

  FREE_C_HEAP_ARRAY(T*, _queues);

}

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

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

  _elems = ArrayAllocator<E>::allocate(N, F);

}

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

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

  ArrayAllocator<E>::free(const_cast<E*>(_elems), N);

}

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);

    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);

    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;

}

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

inline bool OverflowTaskQueue<E, F, N>::try_push_to_taskqueue(E t) {

  return taskqueue_t::push(t);

}

// 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 threshold) {

  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 <= threshold) 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.

    // The barrier is required to prevent reordering the two reads of _age:

    // one is the _age.get() below, and the other is _age.top() above the if-stmt.

    // The algorithm may fail if _age.get() reads an older value than _age.top().

    OrderAccess::loadload();

    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.

#ifndef CPU_MULTI_COPY_ATOMIC

  OrderAccess::fence();

#endif

  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;

}

inline int randomParkAndMiller(int *seed0) {

  const int a =      16807;

  const int m = 2147483647;

  const int q =     127773;  /* m div a */

  const int r =       2836;  /* m mod a */

  STATIC_ASSERT(sizeof(int) == 4);

  int seed = *seed0;

  int hi   = seed / q;

  int lo   = seed % q;

  int test = a * lo - r * hi;

  if (test > 0) {

    seed = test;

  } else {

    seed = test + m;

  }

  *seed0 = seed;

  return seed;

}

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

int GenericTaskQueue<E, F, N>::next_random_queue_id() {

  return randomParkAndMiller(&_seed);

}

template<class T, MEMFLAGS F> bool

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

  if (_n > 2) {

    T* const local_queue = _queues[queue_num];

    uint k1 = queue_num;

    if (local_queue->is_last_stolen_queue_id_valid()) {

      k1 = local_queue->last_stolen_queue_id();

      assert(k1 != queue_num, "Should not be the same");

    } else {

      while (k1 == queue_num) {

        k1 = local_queue->next_random_queue_id() % _n;

      }

    }

    uint k2 = queue_num;

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

      k2 = local_queue->next_random_queue_id() % _n;

    }

    // Sample both and try the larger.

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

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

    uint sel_k = 0;

    bool suc = false;

    if (sz2 > sz1) {

      sel_k = k2;

      suc = _queues[k2]->pop_global(t);

    } else if (sz1 > 0) {

      sel_k = k1;

      suc = _queues[k1]->pop_global(t);

    }

    if (suc) {

      local_queue->set_last_stolen_queue_id(sel_k);

    } else {

      local_queue->invalidate_last_stolen_queue_id();

    }

    return suc;

  } 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, E& t) {

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

    TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal_attempt());

    if (steal_best_of_2(queue_num, t)) {

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

      return true;

    }

  }

  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 Atomic::cmpxchg(new_age._data, &_data, old_age._data);

}

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

template<class Fn>

inline void GenericTaskQueue<E, F, N>::iterate(Fn fn) {

  uint iters = size();

  uint index = _bottom;

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

    index = decrement_index(index);

    fn(const_cast<E&>(_elems[index])); // cast away volatility

  }

}

#endif // SHARE_GC_SHARED_TASKQUEUE_INLINE_HPP