c# – ConcurrentStack：如何检查是否包含对象？

如何检查它是否包含堆栈中的特定对象？

private ConcurrentStack<int> cs = new ConcurrentStack<int>();
cs.Push(1);

方法 Stack<T>.Contains在 ConcurrentStack<T>-class中不可用.我想因为那不是线程安全的.

因此,如果您需要它,您必须使用锁,然后您可以使用Enumerable.Contains：

private ConcurrentStack<int> cs = new ConcurrentStack<int>();
private Object csLockObject  = new Object();

…

bool contains = false;
lock (csLockObject)
{
    contains = cs.Contains(1);
}

但是,当您枚举此快照时,另一个线程可能会向堆栈添加项目或从堆栈中删除项目.如果您想要防止在添加/删除的位置还需要锁定.

I want to avoid duplicates

好吧,你可以使用这样的类,它使用ConcurrentDictionary来检查它是否是唯一的：

public class ConcurrentUniqueStack<T>
{
    private readonly ConcurrentDictionary<T, int> _itemUnique; // there is no ConcurrentHashSet so we need to use a Key-only dictionary
    private readonly ConcurrentStack<T> _stack;

    public ConcurrentUniqueStack() : this(EqualityComparer<T>.Default)
    {
    }
    public ConcurrentUniqueStack(IEqualityComparer<T> comparer)
    {
        _stack = new ConcurrentStack<T>();
        _itemUnique = new ConcurrentDictionary<T, int>(comparer);
    }

    public bool TryPush(T item)
    {
        bool unique = _itemUnique.TryAdd(item, 1);
        if (unique)
        {
            _stack.Push(item);
        }

        return unique;
    }
    public bool TryPop(out T result)
    {
        bool couldBeRemoved = _stack.TryPop(out result);
        if (couldBeRemoved)
        {
            _itemUnique.TryRemove(result, out int whatever);
        }
        return couldBeRemoved;
    }

    public bool TryPeek(out T result) => _stack.TryPeek(out result);
}