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 //
 // detail/timer_queue.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
 #ifndef BOOST_ASIO_DETAIL_TIMER_QUEUE_HPP
 #define BOOST_ASIO_DETAIL_TIMER_QUEUE_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <cstddef>
 #include <vector>
 #include <boost/asio/detail/cstdint.hpp>
 #include <boost/asio/detail/date_time_fwd.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/detail/op_queue.hpp>
 #include <boost/asio/detail/timer_queue_base.hpp>
 #include <boost/asio/detail/wait_op.hpp>
 #include <boost/asio/error.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 template <typename Time_Traits>
 class timer_queue
   : public timer_queue_base
 {
 public:
   // The time type.
   typedef typename Time_Traits::time_type time_type;
 
   // The duration type.
   typedef typename Time_Traits::duration_type duration_type;
 
   // Per-timer data.
   class per_timer_data
   {
   public:
     per_timer_data() :
       heap_index_((std::numeric_limits<std::size_t>::max)()),
       next_(0), prev_(0)
     {
     }
 
   private:
     friend class timer_queue;
 
     // The operations waiting on the timer.
     op_queue<wait_op> op_queue_;
 
     // The index of the timer in the heap.
     std::size_t heap_index_;
 
     // Pointers to adjacent timers in a linked list.
     per_timer_data* next_;
     per_timer_data* prev_;
   };
 
   // Constructor.
   timer_queue()
     : timers_(),
       heap_()
   {
   }
 
   // Add a new timer to the queue. Returns true if this is the timer that is
   // earliest in the queue, in which case the reactor's event demultiplexing
   // function call may need to be interrupted and restarted.
   bool enqueue_timer(const time_type& time, per_timer_data& timer, wait_op* op)
   {
     // Enqueue the timer object.
     if (timer.prev_ == 0 && &timer != timers_)
     {
       if (this->is_positive_infinity(time))
       {
         // No heap entry is required for timers that never expire.
         timer.heap_index_ = (std::numeric_limits<std::size_t>::max)();
       }
       else
       {
         // Put the new timer at the correct position in the heap. This is done
         // first since push_back() can throw due to allocation failure.
         timer.heap_index_ = heap_.size();
         heap_entry entry = { time, &timer };
         heap_.push_back(entry);
         up_heap(heap_.size() - 1);
       }
 
       // Insert the new timer into the linked list of active timers.
       timer.next_ = timers_;
       timer.prev_ = 0;
       if (timers_)
         timers_->prev_ = &timer;
       timers_ = &timer;
     }
 
     // Enqueue the individual timer operation.
     timer.op_queue_.push(op);
 
     // Interrupt reactor only if newly added timer is first to expire.
     return timer.heap_index_ == 0 && timer.op_queue_.front() == op;
   }
 
   // Whether there are no timers in the queue.
   virtual bool empty() const
   {
     return timers_ == 0;
   }
 
   // Get the time for the timer that is earliest in the queue.
   virtual long wait_duration_msec(long max_duration) const
   {
     if (heap_.empty())
       return max_duration;
 
     return this->to_msec(
         Time_Traits::to_posix_duration(
           Time_Traits::subtract(heap_[0].time_, Time_Traits::now())),
         max_duration);
   }
 
   // Get the time for the timer that is earliest in the queue.
   virtual long wait_duration_usec(long max_duration) const
   {
     if (heap_.empty())
       return max_duration;
 
     return this->to_usec(
         Time_Traits::to_posix_duration(
           Time_Traits::subtract(heap_[0].time_, Time_Traits::now())),
         max_duration);
   }
 
   // Dequeue all timers not later than the current time.
   virtual void get_ready_timers(op_queue<operation>& ops)
   {
     if (!heap_.empty())
     {
       const time_type now = Time_Traits::now();
       while (!heap_.empty() && !Time_Traits::less_than(now, heap_[0].time_))
       {
         per_timer_data* timer = heap_[0].timer_;
         while (wait_op* op = timer->op_queue_.front())
         {
           timer->op_queue_.pop();
           op->ec_ = boost::system::error_code();
           ops.push(op);
         }
         remove_timer(*timer);
       }
     }
   }
 
   // Dequeue all timers.
   virtual void get_all_timers(op_queue<operation>& ops)
   {
     while (timers_)
     {
       per_timer_data* timer = timers_;
       timers_ = timers_->next_;
       ops.push(timer->op_queue_);
       timer->next_ = 0;
       timer->prev_ = 0;
     }
 
     heap_.clear();
   }
 
   // Cancel and dequeue operations for the given timer.
   std::size_t cancel_timer(per_timer_data& timer, op_queue<operation>& ops,
       std::size_t max_cancelled = (std::numeric_limits<std::size_t>::max)())
   {
     std::size_t num_cancelled = 0;
     if (timer.prev_ != 0 || &timer == timers_)
     {
       while (wait_op* op = (num_cancelled != max_cancelled)
           ? timer.op_queue_.front() : 0)
       {
         op->ec_ = boost::asio::error::operation_aborted;
         timer.op_queue_.pop();
         ops.push(op);
         ++num_cancelled;
       }
       if (timer.op_queue_.empty())
         remove_timer(timer);
     }
     return num_cancelled;
   }
 
   // Cancel and dequeue a specific operation for the given timer.
   void cancel_timer_by_key(per_timer_data* timer,
       op_queue<operation>& ops, void* cancellation_key)
   {
     if (timer->prev_ != 0 || timer == timers_)
     {
       op_queue<wait_op> other_ops;
       while (wait_op* op = timer->op_queue_.front())
       {
         timer->op_queue_.pop();
         if (op->cancellation_key_ == cancellation_key)
         {
           op->ec_ = boost::asio::error::operation_aborted;
           ops.push(op);
         }
         else
           other_ops.push(op);
       }
       timer->op_queue_.push(other_ops);
       if (timer->op_queue_.empty())
         remove_timer(*timer);
     }
   }
 
   // Move operations from one timer to another, empty timer.
   void move_timer(per_timer_data& target, per_timer_data& source)
   {
     target.op_queue_.push(source.op_queue_);
 
     target.heap_index_ = source.heap_index_;
     source.heap_index_ = (std::numeric_limits<std::size_t>::max)();
 
     if (target.heap_index_ < heap_.size())
       heap_[target.heap_index_].timer_ = &target;
 
     if (timers_ == &source)
       timers_ = &target;
     if (source.prev_)
       source.prev_->next_ = &target;
     if (source.next_)
       source.next_->prev_= &target;
     target.next_ = source.next_;
     target.prev_ = source.prev_;
     source.next_ = 0;
     source.prev_ = 0;
   }
 
 private:
   // Move the item at the given index up the heap to its correct position.
   void up_heap(std::size_t index)
   {
     while (index > 0)
     {
       std::size_t parent = (index - 1) / 2;
       if (!Time_Traits::less_than(heap_[index].time_, heap_[parent].time_))
         break;
       swap_heap(index, parent);
       index = parent;
     }
   }
 
   // Move the item at the given index down the heap to its correct position.
   void down_heap(std::size_t index)
   {
     std::size_t child = index * 2 + 1;
     while (child < heap_.size())
     {
       std::size_t min_child = (child + 1 == heap_.size()
           || Time_Traits::less_than(
             heap_[child].time_, heap_[child + 1].time_))
         ? child : child + 1;
       if (Time_Traits::less_than(heap_[index].time_, heap_[min_child].time_))
         break;
       swap_heap(index, min_child);
       index = min_child;
       child = index * 2 + 1;
     }
   }
 
   // Swap two entries in the heap.
   void swap_heap(std::size_t index1, std::size_t index2)
   {
     heap_entry tmp = heap_[index1];
     heap_[index1] = heap_[index2];
     heap_[index2] = tmp;
     heap_[index1].timer_->heap_index_ = index1;
     heap_[index2].timer_->heap_index_ = index2;
   }
 
   // Remove a timer from the heap and list of timers.
   void remove_timer(per_timer_data& timer)
   {
     // Remove the timer from the heap.
     std::size_t index = timer.heap_index_;
     if (!heap_.empty() && index < heap_.size())
     {
       if (index == heap_.size() - 1)
       {
         timer.heap_index_ = (std::numeric_limits<std::size_t>::max)();
         heap_.pop_back();
       }
       else
       {
         swap_heap(index, heap_.size() - 1);
         timer.heap_index_ = (std::numeric_limits<std::size_t>::max)();
         heap_.pop_back();
         if (index > 0 && Time_Traits::less_than(
               heap_[index].time_, heap_[(index - 1) / 2].time_))
           up_heap(index);
         else
           down_heap(index);
       }
     }
 
     // Remove the timer from the linked list of active timers.
     if (timers_ == &timer)
       timers_ = timer.next_;
     if (timer.prev_)
       timer.prev_->next_ = timer.next_;
     if (timer.next_)
       timer.next_->prev_= timer.prev_;
     timer.next_ = 0;
     timer.prev_ = 0;
   }
 
   // Determine if the specified absolute time is positive infinity.
   template <typename Time_Type>
   static bool is_positive_infinity(const Time_Type&)
   {
     return false;
   }
 
   // Determine if the specified absolute time is positive infinity.
   template <typename T, typename TimeSystem>
   static bool is_positive_infinity(
       const boost::date_time::base_time<T, TimeSystem>& time)
   {
     return time.is_pos_infinity();
   }
 
   // Helper function to convert a duration into milliseconds.
   template <typename Duration>
   long to_msec(const Duration& d, long max_duration) const
   {
     if (d.ticks() <= 0)
       return 0;
     int64_t msec = d.total_milliseconds();
     if (msec == 0)
       return 1;
     if (msec > max_duration)
       return max_duration;
     return static_cast<long>(msec);
   }
 
   // Helper function to convert a duration into microseconds.
   template <typename Duration>
   long to_usec(const Duration& d, long max_duration) const
   {
     if (d.ticks() <= 0)
       return 0;
     int64_t usec = d.total_microseconds();
     if (usec == 0)
       return 1;
     if (usec > max_duration)
       return max_duration;
     return static_cast<long>(usec);
   }
 
   // The head of a linked list of all active timers.
   per_timer_data* timers_;
 
   struct heap_entry
   {
     // The time when the timer should fire.
     time_type time_;
 
     // The associated timer with enqueued operations.
     per_timer_data* timer_;
   };
 
   // The heap of timers, with the earliest timer at the front.
   std::vector<heap_entry> heap_;
 };
 
 } // namespace detail
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_DETAIL_TIMER_QUEUE_HPP

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