using System.Collections;
using System.Collections.Generic;


namespace DepthFirstScheduler
{
    public class LockQueue<T> where T : class
    {
        List<T> m_queue = new List<T>();
        public int Count
        {
            get
            {
                lock (((ICollection)m_queue).SyncRoot)
                {
                    return m_queue.Count;
                }
            }
        }

        public void Enqueue(T t)
        {
            lock (((ICollection)m_queue).SyncRoot)
            {
                m_queue.Add(t);
            }
        }

        public T Dequeue(out int remain)
        {
            lock (((ICollection)m_queue).SyncRoot)
            {
                if (m_queue.Count == 0)
                {
                    remain = 0;
                    return null;
                }
                var item = m_queue[0];
                m_queue.RemoveAt(0);
                remain = m_queue.Count;
                return item;
            }
        }

        public T Dequeue()
        {
            lock (((ICollection)m_queue).SyncRoot)
            {
                if (m_queue.Count == 0) return null;
                var item = m_queue[0];
                m_queue.RemoveAt(0);
                return item;
            }
        }
    }

    public class LockQueueForValue<T> where T : struct
    {
        List<T> m_queue = new List<T>();
        public int Count
        {
            get
            {
                lock (((ICollection)m_queue).SyncRoot)
                {
                    return m_queue.Count;
                }
            }
        }

        public void Enqueue(T t)
        {
            lock (((ICollection)m_queue).SyncRoot)
            {
                m_queue.Add(t);
            }
        }

        public bool TryDequeue(out T t)
        {
            lock (((ICollection)m_queue).SyncRoot)
            {
                if (m_queue.Count == 0)
                {
                    t = default(T);
                    return false;
                }

                t = m_queue[0];
                m_queue.RemoveAt(0);
                return true;
            }
        }
    }
}