/*

 * Copyright (c) 2001, 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

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#ifndef SHARE_GC_SHARED_TASKQUEUE_HPP

#define SHARE_GC_SHARED_TASKQUEUE_HPP

#include "memory/allocation.hpp"

#include "memory/padded.hpp"

#include "oops/oopsHierarchy.hpp"

#include "utilities/ostream.hpp"

#include "utilities/stack.hpp"

// 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_attempt() { ++_stats[steal_attempt]; }

  inline void record_steal()         { ++_stats[steal]; }

  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_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

// TaskQueueSuper collects functionality common to all GenericTaskQueue instances.

template <unsigned int N, MEMFLAGS F>

class TaskQueueSuper: public CHeapObj<F> {

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;

    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;)

};

//

// GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-

// ended-queue (deque), intended for use in work stealing. Queue operations

// are non-blocking.

//

// A queue owner thread performs push() and pop_local() operations on one end

// of the queue, while other threads may steal work using the pop_global()

// method.

//

// The main difference to the original algorithm is that this

// implementation allows wrap-around at the end of its allocated

// storage, which is an array.

//

// The original paper is:

//

// Arora, N. S., Blumofe, R. D., and Plaxton, C. G.

// Thread scheduling for multiprogrammed multiprocessors.

// Theory of Computing Systems 34, 2 (2001), 115-144.

//

// The following paper provides an correctness proof and an

// implementation for weakly ordered memory models including (pseudo-)

// code containing memory barriers for a Chase-Lev deque. Chase-Lev is

// similar to ABP, with the main difference that it allows resizing of the

// underlying storage:

//

// Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.

// Correct and efficient work-stealing for weak memory models

// Proceedings of the 18th ACM SIGPLAN symposium on Principles and

// practice of parallel programming (PPoPP 2013), 69-80

//

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

class GenericTaskQueue: public TaskQueueSuper<N, F> {

protected:

  typedef typename TaskQueueSuper<N, F>::Age Age;

  typedef typename TaskQueueSuper<N, F>::idx_t idx_t;

  using TaskQueueSuper<N, F>::_bottom;

  using TaskQueueSuper<N, F>::_age;

  using TaskQueueSuper<N, F>::increment_index;

  using TaskQueueSuper<N, F>::decrement_index;

  using TaskQueueSuper<N, F>::dirty_size;

public:

  using TaskQueueSuper<N, F>::max_elems;

  using TaskQueueSuper<N, F>::size;

#if  TASKQUEUE_STATS

  using TaskQueueSuper<N, F>::stats;

#endif

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) as long as the number of entries exceeds the threshold.

  // If successful, returns true and sets t to the task; otherwise, returns false

  // (the queue is empty or the number of elements below the threshold).

  inline bool pop_local(volatile E& t, uint threshold = 0);

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

  // recently pushed).

  bool pop_global(volatile E& t);

  // Delete any resource associated with the queue.

  ~GenericTaskQueue();

  // Apply fn to each element in the task queue.  The queue must not

  // be modified while iterating.

  template<typename Fn> void iterate(Fn fn);

private:

  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);

  // Element array.

  volatile E* _elems;

  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(E*));

  // Queue owner local variables. Not to be accessed by other threads.

  static const uint InvalidQueueId = uint(-1);

  uint _last_stolen_queue_id; // The id of the queue we last stole from

  int _seed; // Current random seed used for selecting a random queue during stealing.

  DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(uint) + sizeof(int));

public:

  int next_random_queue_id();

  void set_last_stolen_queue_id(uint id)     { _last_stolen_queue_id = id; }

  uint last_stolen_queue_id() const          { return _last_stolen_queue_id; }

  bool is_last_stolen_queue_id_valid() const { return _last_stolen_queue_id != InvalidQueueId; }

  void invalidate_last_stolen_queue_id()     { _last_stolen_queue_id = InvalidQueueId; }

};

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

GenericTaskQueue<E, F, N>::GenericTaskQueue() : _last_stolen_queue_id(InvalidQueueId), _seed(17 /* random number */) {

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

}

// 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, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>

class OverflowTaskQueue: public GenericTaskQueue<E, F, N>

{

public:

  typedef Stack<E, F>               overflow_t;

  typedef GenericTaskQueue<E, F, 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);

  // Try to push task t onto the queue only. Returns true if successful, false otherwise.

  inline bool try_push_to_taskqueue(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;

};

class TaskQueueSetSuper {

public:

  // Returns "true" if some TaskQueue in the set contains a task.

  virtual bool peek() = 0;

  // Tasks in queue

  virtual uint tasks() const = 0;

};

template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {

};

template<class T, MEMFLAGS F>

class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {

public:

  typedef typename T::element_type E;

private:

  uint _n;

  T** _queues;

  bool steal_best_of_2(uint queue_num, E& t);

public:

  GenericTaskQueueSet(uint n);

  ~GenericTaskQueueSet();

  void register_queue(uint i, T* q);

  T* queue(uint n);

  // Try to steal a task from some other queue than queue_num. It may perform several attempts at doing so.

  // Returns if stealing succeeds, and sets "t" to the stolen task.

  bool steal(uint queue_num, E& t);

  bool peek();

  uint tasks() const;

  uint size() const { return _n; }

};

template<class T, MEMFLAGS F> void

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

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

  _queues[i] = q;

}

template<class T, MEMFLAGS F> T*

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

  return _queues[i];

}

template<class T, MEMFLAGS F>

bool GenericTaskQueueSet<T, F>::peek() {

  // Try all the queues.

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

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

      return true;

  }

  return false;

}

template<class T, MEMFLAGS F>

uint GenericTaskQueueSet<T, F>::tasks() const {

  uint n = 0;

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

    n += _queues[j]->size();

  }

  return n;

}

// When to terminate from the termination protocol.

class TerminatorTerminator: public CHeapObj<mtInternal> {

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 CHeapObj<mtGC> {

protected:

  uint _n_threads;

  TaskQueueSetSuper* _queue_set;

  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);

  volatile uint _offered_termination;

  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile uint));

#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(uint 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