DotNet 源码学习——QUEUE

1、Queue声明创建对象。(Queue为泛型对象。)

public class Queue<T> :IEnumerable<T>,System.Collections.ICollection,IReadOnlyCollection<T>

本质为Array对象存储数据。

Queue<string> qy = new Queue<string>();
private T[] _array
public Queue()
{
    _array = Array.Empty<T>();
}
Queue<int> qy1 = new Queue<int>();
public Queue(int capacity)
{
    if (capacity < )
        throw new ArgumentOutOfRangeException(nameof(capacity), capacity, SR.ArgumentOutOfRange_NeedNonNegNum);
    _array = new T[capacity];
}

Queue<int> qy2 = new Queue<int>(new List<int>());

public Queue(IEnumerable<T> collection)
{
    if (collection == null)
        throw new ArgumentNullException(nameof(collection));

    _array = EnumerableHelpers.ToArray(collection, out _size);
    if (_size != _array.Length) _tail = _size;
}

2、队列的空间是实际存储值的两倍，如果小于两倍则每次增场4的长度。

 if (_size == _array.Length)
 {
      int newcapacity = (int)((long)_array.Length * (long)GrowFactor / );
      if (newcapacity < _array.Length + MinimumGrow)
      {
          newcapacity = _array.Length + MinimumGrow;
      }
      SetCapacity(newcapacity);
 }

3、Queue为先进先出。

进队列在数组末尾赋值

        public void Enqueue(T item)
        {
            if (_size == _array.Length)
            {
                int newcapacity = (int)((long)_array.Length * (long)GrowFactor / );
                if (newcapacity < _array.Length + MinimumGrow)
                {
                    newcapacity = _array.Length + MinimumGrow;
                }
                SetCapacity(newcapacity);
            }

            _array[_tail] = item;
            MoveNext(ref _tail);
            _size++;
            _version++;
        }

出队列则从头部取值

        public T Dequeue()
        {
            int head = _head;
            T[] array = _array;

            if (_size == )
            {
                ThrowForEmptyQueue();
            }

            T removed = array[head];
            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
            {
                array[head] = default!;
            }
            MoveNext(ref _head);
            _size--;
            _version++;
            return removed;
        }    

4、TryDequeue 与 Dequeue()区别在于 TryDequeue 判断size为0时，返回false 并out 泛型的默认值

        public bool TryDequeue([MaybeNullWhen(false)] out T result)
        {
            int head = _head;
            T[] array = _array;

            if (_size == )
            {
                result = default!;
                return false;
            }

            result = array[head];
            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
            {
                array[head] = default!;
            }
            MoveNext(ref _head);
            _size--;
            _version++;
            return true;
        }    

注：MaybeNullWhenAttribute(Boolean) 返回值条件。 如果方法返回此值，则关联的参数可能为 null

5、Peek 仅仅时查看一下下一个要返回的值，不从数组移除

            if (_size == )
            {
                result = default!;
                return false;
            }

            result = _array[_head];
            return true;            

随是拙见，但为原创，转载注明出处，敬谢

Queue 常用的方法大约就这些。先写道这里，碎觉。

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