设置 CancellationToken 时抛出任意异常是不好的做法吗？

Question

当检测到CancellationToken.IsCancelRequested 时，通过抛出OperationCancelledException 以外的其他内容让我的库打破方法是不好的做法吗？

例如：

async Task<TcpClient> ConnectAsync(string host, int port, CancellationToken ct)
{
    var client = new TcpClient();
    try
    {
        using (ct.Register(client.Close, true))
        {
            await client.ConnectAsync(host, port);
        }

        // Pick up strugglers here because ct.Register() may have hosed our client
        ct.ThrowIfCancellationRequested();
    }
    catch (Exception)
    {
        client.Close();
        throw;
    }

    return client;
}

取消后，这有可能根据时间抛出ObjectDisposedException 或NullReferenceException。 （因为TcpClient.ConnectAsync() 可以在同时调用TcpClient.Close() 时抛出任何一个。）

现在，我可以像这样修复：

async Task<TcpClient> ConnectAsync(string host, int port, CancellationToken ct)
{
    var client = new TcpClient();
    try
    {
        using (ct.Register(client.Close, true))
        {
            try
            {
                await client.ConnectAsync(host, port);
            }
            catch (Exception)
            {
                // These exceptions are likely because we closed the
                // connection with ct.Register().  Convert them to
                // OperationCancelledException if that's the case
                ct.ThrowIfCancellationRequested();
                throw;
            }
        }

        // Pick up strugglers here because ct.Register() may have hosed our client
        ct.ThrowIfCancellationRequested();
    }
    catch (Exception)
    {
        client.Close();
        throw;
    }

    return client;
}

同样适用于调用层次结构的每一层：

async Task<TcpClient> ConnectSslStreamAsync(string host, int port, CancellationToken ct)
{
    var client = await ConnectAsync(host, port, ct);
    try
    {
        ct.ThrowIfCancellationRequested();

        var sslStream = new SslStream(client.getStream());
        using (ct.Register(sslStream.Close))
        {
            try
            {
                await sslStream.AuthenticateAsClientAsync(...);
            }
            catch (Exception)
            {
                // These exceptions are likely because we closed the
                // stream with ct.Register().  Convert them to
                // OperationCancelledException if that's the case
                ct.ThrowIfCancellationRequested();
                throw;
            }
        }

        // Pick up strugglers here because ct.Register() may have hosed our stream
        ct.ThrowIfCancellationRequested();
    }
    catch (Exception)
    {
        client.Close();
        throw;
    }

    return client;
}

但这会添加这些额外的代码，而实际上，只需要在最外层进行一次检查即可。 （在取消源处。）

让这些任意异常发生是不好的做法吗？还是在最外层的调用者常规忽略它们？

Answer 1

如果请求取消，您应该抛出 OperationCancelledException。当您的代码的使用者遇到异常时，他们将不知道这实际上是取消还是其他原因。

也就是说，如果您因为注册关闭委托而无法抛出OperationCancelledException，您可以尝试here 提供的方法，您将创建一个用于关闭 tcpClient 或流的任务并验证哪个任务首先完成并采取相应措施。