// -*- C++ -*-

//=============================================================================
/**
 *  @file    Timer_Heap_T.h
 *
 *  @author Douglas C. Schmidt <d.schmidt@vanderbilt.edu>
 */
//=============================================================================

#ifndef ACE_TIMER_HEAP_T_H
#define ACE_TIMER_HEAP_T_H
#include /**/ "ace/pre.h"

#include "ace/Timer_Queue_T.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include "ace/Free_List.h"
#include "ace/Unbounded_Set.h"

ACE_BEGIN_VERSIONED_NAMESPACE_DECL

// Forward declaration
template <class TYPE, class FUNCTOR, class ACE_LOCK, typename TIME_POLICY>
class ACE_Timer_Heap_T;

/**
 * @class ACE_Timer_Heap_Iterator_T
 *
 * @brief Iterates over an ACE_Timer_Heap_T.
 *
 * This is a generic iterator that can be used to visit every
 * node of a timer queue.  Be aware that it doesn't transverse
 * in the order of timeout values.
 */
template <class TYPE, class FUNCTOR, class ACE_LOCK, typename TIME_POLICY = ACE_Default_Time_Policy>
class ACE_Timer_Heap_Iterator_T : public ACE_Timer_Queue_Iterator_T<TYPE>
{
public:
  typedef ACE_Timer_Heap_T<TYPE, FUNCTOR, ACE_LOCK, TIME_POLICY> Heap;
  /// Constructor.
  ACE_Timer_Heap_Iterator_T (Heap &);

  /// Destructor.
  ~ACE_Timer_Heap_Iterator_T () override = default;

  /// Positions the iterator at the earliest node in the Timer Queue
  void first () override;

  /// Positions the iterator at the next node in the Timer Queue
  void next () override;

  /// Returns true when there are no more nodes in the sequence
  bool isdone () const override;

  /// Returns the node at the current position in the sequence
  ACE_Timer_Node_T<TYPE> *item () override;

  /// Declare the dynamic allocation hooks.
  ACE_ALLOC_HOOK_DECLARE;

protected:
  /// Pointer to the ACE_Timer_Heap that we are iterating over.
  Heap & timer_heap_;

  /// Position in the array where the iterator is at
  size_t position_;
};

/**
 * @class ACE_Timer_Heap_T
 *
 * @brief Provides a very fast and predictable timer implementation.
 *
 * This implementation uses a heap-based callout queue of
 * absolute times.  Therefore, in the average and worst case,
 * scheduling, canceling, and expiring timers is O(log N) (where
 * N is the total number of timers).  In addition, we can also
 * preallocate as many @c ACE_Timer_Node objects as there are slots
 * in the heap.  This allows us to completely remove the need for
 * dynamic memory allocation, which is important for real-time
 * systems.
 */
template <class TYPE, class FUNCTOR, class ACE_LOCK, typename TIME_POLICY = ACE_Default_Time_Policy>
class ACE_Timer_Heap_T : public ACE_Timer_Queue_T<TYPE, FUNCTOR, ACE_LOCK, TIME_POLICY>
{
public:
  typedef ACE_Timer_Heap_Iterator_T<TYPE, FUNCTOR, ACE_LOCK, TIME_POLICY> HEAP_ITERATOR;
  friend class ACE_Timer_Heap_Iterator_T<TYPE, FUNCTOR, ACE_LOCK, TIME_POLICY>;

  typedef ACE_Timer_Queue_T<TYPE, FUNCTOR, ACE_LOCK, TIME_POLICY> Base_Time_Policy;

  /**
   * The Constructor creates a heap with specified number of elements.
   * This can also take in a upcall functor and freelist (if 0, then
   * defaults will be created).
   *
   * @param size The maximum number of timers that can be
   * inserted into the new object.
   * @param preallocated Default false, true then all the memory
   * for the @c ACE_Timer_Node objects will be pre-allocated. This saves
   * time and is more predictable (though it requires more space).
   * Otherwise, timer nodes are allocated as needed.
   * @param freelist is the freelist of timer nodes.
   * @param upcall_functor If 0 Timer Heap will create a default FUNCTOR.
   */
  ACE_Timer_Heap_T (size_t size,
                    bool preallocated = false,
                    FUNCTOR *upcall_functor = 0,
                    ACE_Free_List<ACE_Timer_Node_T <TYPE> > *freelist = 0,
                    TIME_POLICY const & time_policy = TIME_POLICY());

  /**
   * Default constructor. @c upcall_functor is the instance of the
   * FUNCTOR to be used by the queue. If @c upcall_functor is 0, Timer
   * Heap will create a default FUNCTOR.  @c freelist is the freelist of
   * timer nodes.  If 0, then a default freelist will be created.  The default
   * size will be ACE_DEFAULT_TIMERS and there will be no preallocation.
   */
  ACE_Timer_Heap_T (FUNCTOR *upcall_functor = 0,
                    ACE_Free_List<ACE_Timer_Node_T <TYPE> > *freelist = 0,
                    TIME_POLICY const & time_policy = TIME_POLICY());

  /// Destructor.
  virtual ~ACE_Timer_Heap_T ();

  /// True if heap is empty, else false.
  virtual bool is_empty () const;

  /// Returns the time of the earliest node in the Timer_Queue.
  /// Must be called on a non-empty queue.
  virtual const ACE_Time_Value &earliest_time () const;

  /**
   * Resets the interval of the timer represented by @a timer_id to
   * @a interval, which is specified in relative time to the current
   * <gettimeofday>.  If @a interval is equal to
   * ACE_Time_Value::zero, the timer will become a non-rescheduling
   * timer.  Returns 0 if successful, -1 if not.
   */
  virtual int reset_interval (long timer_id,
                              const ACE_Time_Value &interval);

  /**
   * Cancel all timers associated with @a type.  If @a dont_call_handle_close
   * is 0 then the <functor> will be invoked.  Returns number of timers
   * cancelled.
   */
  virtual int cancel (const TYPE &type,
                      int dont_call_handle_close = 1);

  /**
   * Cancel the single timer that matches the @a timer_id value (which
   * was returned from the <schedule> method).  If act is non-NULL
   * then it will be set to point to the ``magic cookie'' argument
   * passed in when the timer was registered.  This makes it possible
   * to free up the memory and avoid memory leaks. If @a dont_call_handle_close
   * is 0 then the <functor> will be invoked.  Returns 1 if cancellation
   * succeeded and 0 if the @a timer_id wasn't found.
   */
  virtual int cancel (long timer_id,
                      const void **act = 0,
                      int dont_call_handle_close = 1);

  /**
   * Destroy timer queue. Cancels all timers.
   */
  virtual int close ();

  /// Returns a pointer to this ACE_Timer_Queue's iterator.
  virtual ACE_Timer_Queue_Iterator_T<TYPE> &iter ();

  /**
   * Removes the earliest node from the queue and returns it. Note that
   * the timer is removed from the heap, but is not freed, and its ID
   * is not reclaimed. The caller is responsible for calling either
   * @c reschedule() or @c free_node() after this function returns. Thus,
   * this function is for support of @c ACE_Timer_Queue::expire and
   * should not be used unadvisedly in other conditions.
   */
  ACE_Timer_Node_T <TYPE> *remove_first ();

  /// Dump the state of an object.
  virtual void dump () const;

  /// Reads the earliest node from the queue and returns it.
  virtual ACE_Timer_Node_T<TYPE> *get_first ();

  /// Declare the dynamic allocation hooks.
  ACE_ALLOC_HOOK_DECLARE;

protected:

  /**
   * Schedule a timer that may optionally auto-reset.
   * Schedule @a type that will expire at @a future_time,
   * which is specified in absolute time.  If it expires then @a act is
   * passed in as the value to the <functor>.  If @a interval is != to
   * ACE_Time_Value::zero then it is used to reschedule the @a type
   * automatically, using relative time to the current <gettimeofday>.
   * This method returns a <timer_id> that uniquely identifies the the
   * @a type entry in an internal list.  This <timer_id> can be used to
   * cancel the timer before it expires.  The cancellation ensures
   * that <timer_ids> are unique up to values of greater than 2
   * billion timers.  As long as timers don't stay around longer than
   * this there should be no problems with accidentally deleting the
   * wrong timer.  Returns -1 on failure (which is guaranteed never to
   * be a valid <timer_id>).
   */
  virtual long schedule_i (const TYPE &type,
                           const void *act,
                           const ACE_Time_Value &future_time,
                           const ACE_Time_Value &interval);

  /// Reschedule an "interval" ACE_Timer_Node.
  virtual void reschedule (ACE_Timer_Node_T<TYPE> *);

  /// Factory method that allocates a new node (uses operator new if
  /// we're *not* preallocating, otherwise uses an internal freelist).
  virtual ACE_Timer_Node_T<TYPE> *alloc_node ();

  /**
   * Factory method that frees a previously allocated node (uses
   * operator delete if we're *not* preallocating, otherwise uses an
   * internal freelist).
   */
  virtual void free_node (ACE_Timer_Node_T<TYPE> *);

private:
  /// Remove and return the @a sloth ACE_Timer_Node and restore the
  /// heap property.
  ACE_Timer_Node_T<TYPE> *remove (size_t slot);

  /// Insert @a new_node into the heap and restore the heap property.
  void insert (ACE_Timer_Node_T<TYPE> *new_node);

  /**
   * Doubles the size of the heap and the corresponding timer_ids array.
   * If preallocation is used, will also double the size of the
   * preallocated array of ACE_Timer_Nodes.
   */
  void grow_heap ();

  /// Restore the heap property, starting at @a slot.
  void reheap_up (ACE_Timer_Node_T<TYPE> *new_node,
                  size_t slot,
                  size_t parent);

  /// Restore the heap property, starting at @a slot.
  void reheap_down (ACE_Timer_Node_T<TYPE> *moved_node,
                    size_t slot,
                    size_t child);

  /// Copy @a moved_node into the @a slot slot of <heap_> and move
  /// @a slot into the corresponding slot in the <timer_id_> array.
  void copy (size_t slot, ACE_Timer_Node_T<TYPE> *moved_node);

  /**
   * Returns a timer id that uniquely identifies this timer.  This id
   * can be used to cancel a timer via the <cancel (int)> method.  The
   * timer id returned from this method will never == -1 to avoid
   * conflicts with other failure return values.
   */
  long timer_id ();

  /// Pops and returns a new timer id from the freelist.
  long pop_freelist ();

  /// Pushes @a old_id onto the freelist.
  void push_freelist (long old_id);

  /// Maximum size of the heap.
  size_t max_size_;

  /// Current size of the heap.
  size_t cur_size_;

  /// Number of heap entries in transition (removed from the queue, but
  /// not freed) and may be rescheduled or freed.
  size_t cur_limbo_;

  /// Iterator used to expire timers.
  HEAP_ITERATOR *iterator_;

  /**
   * Current contents of the Heap, which is organized as a "heap" of
   * ACE_Timer_Node *'s.  In this context, a heap is a "partially
   * ordered, almost complete" binary tree, which is stored in an
   * array.
   */
  ACE_Timer_Node_T<TYPE> **heap_;

  /**
   * An array of "pointers" that allows each ACE_Timer_Node in the
   * <heap_> to be located in O(1) time.  Basically, <timer_id_[i]>
   * contains the slot in the <heap_> array where an ACE_Timer_Node
   * * with timer id \<i\> resides.  Thus, the timer id passed back from
   * <schedule> is really a slot into the <timer_ids> array.  The
   * <timer_ids_> array serves two purposes: negative values are
   * indications of free timer IDs, whereas positive values are
   * "pointers" into the <heap_> array for assigned timer IDs.
   */
  ssize_t *timer_ids_;

  /// "Pointer" to the element in the <timer_ids_> array that was
  /// last given out as a timer ID.
  size_t timer_ids_curr_;

  /// Index representing the lowest timer ID that has been freed. When
  /// the timer_ids_next_ value wraps around, it starts back at this
  /// point.
  size_t timer_ids_min_free_;

  /**
   * If this is non-0, then we preallocate <max_size_> number of
   * ACE_Timer_Node objects in order to reduce dynamic allocation
   * costs.  In auto-growing implementation, this points to the
   * last array of nodes allocated.
   */
  ACE_Timer_Node_T<TYPE> *preallocated_nodes_;

  /// This points to the head of the <preallocated_nodes_> freelist,
  /// which is organized as a stack.
  ACE_Timer_Node_T<TYPE> *preallocated_nodes_freelist_;

  /// Set of pointers to the arrays of preallocated timer nodes.
  /// Used to delete the allocated memory when required.
  ACE_Unbounded_Set<ACE_Timer_Node_T<TYPE> *> preallocated_node_set_;
};

ACE_END_VERSIONED_NAMESPACE_DECL

#if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
#include "ace/Timer_Heap_T.cpp"
#endif /* ACE_TEMPLATES_REQUIRE_SOURCE */

#if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
#pragma implementation ("Timer_Heap_T.cpp")
#endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */

#include /**/ "ace/post.h"
#endif /* ACE_TIMER_HEAP_T_H */
