/*

 * Copyright (c) 2001, 2010, 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.

 *

 */

// Simple TaskQueue stats that are collected by default in debug builds.

#if !defined(TASKQUEUE_STATS) && defined(ASSERT)

#define TASKQUEUE_STATS 1

#elif !defined(TASKQUEUE_STATS)

#define TASKQUEUE_STATS 0

#endif

#if TASKQUEUE_STATS

#define TASKQUEUE_STATS_ONLY(code) code

#else

#define TASKQUEUE_STATS_ONLY(code)

#endif // TASKQUEUE_STATS

#if TASKQUEUE_STATS

class TaskQueueStats {

public:

  enum StatId {

    push,             // number of taskqueue pushes

    pop,              // number of taskqueue pops

    pop_slow,         // subset of taskqueue pops that were done slow-path

    steal_attempt,    // number of taskqueue steal attempts

    steal,            // number of taskqueue steals

    overflow,         // number of overflow pushes

    overflow_max_len, // max length of overflow stack

    last_stat_id

  };

public:

  inline TaskQueueStats()       { reset(); }

  inline void record_push()     { ++_stats[push]; }

  inline void record_pop()      { ++_stats[pop]; }

  inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }

  inline void record_steal(bool success);

  inline void record_overflow(size_t new_length);

  TaskQueueStats & operator +=(const TaskQueueStats & addend);

  inline size_t get(StatId id) const { return _stats[id]; }

  inline const size_t* get() const   { return _stats; }

  inline void reset();

  // Print the specified line of the header (does not include a line separator).

  static void print_header(unsigned int line, outputStream* const stream = tty,

                           unsigned int width = 10);

  // Print the statistics (does not include a line separator).

  void print(outputStream* const stream = tty, unsigned int width = 10) const;

  DEBUG_ONLY(void verify() const;)

private:

  size_t                    _stats[last_stat_id];

  static const char * const _names[last_stat_id];

};

void TaskQueueStats::record_steal(bool success) {

  ++_stats[steal_attempt];

  if (success) ++_stats[steal];

}

void TaskQueueStats::record_overflow(size_t new_len) {

  ++_stats[overflow];

  if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;

}

void TaskQueueStats::reset() {

  memset(_stats, 0, sizeof(_stats));

}

#endif // TASKQUEUE_STATS

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/does not contain any tasks.

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

  bool is_empty() const { return size() == 0; }

  // 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; }

  TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)

};

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;

  TASKQUEUE_STATS_ONLY(using TaskQueueSuper<N>::stats;)

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);

  // Attempts to claim a task from the "local" end of the queue (the most

  // recently pushed).  If successful, returns true and sets t to the task;

  // otherwise, returns false (the queue is empty).

  inline bool pop_local(E& t);

  // Like pop_local(), but uses the "global" end of the queue (the least

  // recently pushed).

  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);

}

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));

    TASKQUEUE_STATS_ONLY(stats.record_push());

    return true;

  }

  return false;

}

// 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, 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");

      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, 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);

}

// OverflowTaskQueue is a TaskQueue that also includes an overflow stack for

// elements that do not fit in the TaskQueue.

//

// This class hides two methods from super classes:

//

// push() - push onto the task queue or, if that fails, onto the overflow stack

// is_empty() - return true if both the TaskQueue and overflow stack are empty

//

// Note that size() is not hidden--it returns the number of elements in the

// TaskQueue, and does not include the size of the overflow stack.  This

// simplifies replacement of GenericTaskQueues with OverflowTaskQueues.

template<class E, unsigned int N = TASKQUEUE_SIZE>

class OverflowTaskQueue: public GenericTaskQueue<E, N>

{

public:

  typedef Stack<E>               overflow_t;

  typedef GenericTaskQueue<E, N> taskqueue_t;

  TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)

  // Push task t onto the queue or onto the overflow stack.  Return true.

  inline bool push(E t);

  // Attempt to pop from the overflow stack; return true if anything was popped.

  inline bool pop_overflow(E& t);

  inline overflow_t* overflow_stack() { return &_overflow_stack; }

  inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }

  inline bool overflow_empty()  const { return _overflow_stack.is_empty(); }

  inline bool is_empty()        const {

    return taskqueue_empty() && overflow_empty();

  }

private:

  overflow_t _overflow_stack;

};

template <class E, unsigned int N>

bool OverflowTaskQueue<E, 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, unsigned int N>

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

{

  if (overflow_empty()) return false;

  t = overflow_stack()->pop();

  return true;

}

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" to the stolen task, otherwise returns

  // false.

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

  bool peek();