1. 原代码

public async Task SendToClientAsync(TcpClient targetClient, byte[] data, int offset, int length)
{
    try
    {
        // 1. 检查客户端是否有效
        if (targetClient == null || !targetClient.Connected)
        {
            Console.WriteLine("Cannot send: client is not connected");
            return;
        }
        
        // 2. 使用参数中的客户端对象
        NetworkStream stream = targetClient.GetStream();
        
        // 3. 异步写入数据
        await stream.WriteAsync(data, offset, length);
        
        Console.WriteLine("Data sent to client.");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error sending data to client: {ex.Message}");
        // 可添加更多错误处理逻辑，如重试或清理连接
    }
}

解决方案：添加同步机制
方案1：客户端级别的锁（推荐）

private readonly ConcurrentDictionary<TcpClient, SemaphoreSlim> clientLocks = new();

public async Task SendToClientAsync(TcpClient targetClient, byte[] data, int offset, int length)
{
    // 获取或创建客户端专属锁
    var clientLock = clientLocks.GetOrAdd(targetClient, _ => new SemaphoreSlim(1, 1));
    
    await clientLock.WaitAsync();
    try
    {
        if (targetClient.Connected)
        {
            NetworkStream stream = targetClient.GetStream();
            await stream.WriteAsync(data, offset, length);
        }
    }
    finally
    {
        clientLock.Release();
    }
}

方案2：全局锁（简单但性能低）

private readonly object sendLock = new object();

public async Task SendToClientAsync(TcpClient targetClient, byte[] data, int offset, int length)
{
    lock (sendLock) // 全局同步锁
    {
        if (targetClient.Connected)
        {
            NetworkStream stream = targetClient.GetStream();
            stream.Write(data, offset, length); // 注意：同步写入
        }
    }
}