如何在Compact Framework下的套接字上实现非无限接收和发送超时？

Question

在完整的.Net Framework上,我使用以下代码:

socket.SetSocketOption(
  SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, readTimeout);
socket.SetSocketOption(
  SocketOptionLevel.Socket, SocketOptionName.SendTimeout, writeTimeout);

但是,Windows Mobile不支持此操作并抛出异常.

我目前正在测试此解决方案以实现超时.

有谁知道更好的方法？如果可能的话,我想避免产生多个线程,毕竟这是一个嵌入式设备.

Answer 1

此代码有效,可在预期时提高超时(它是我在问题中链接的示例的修改版本):

// copied from Mono, because CF lacks this enum
enum SocketError
{
    IOPending = 997,
    NoBufferSpaceAvailable = 10055,
    TimedOut = 10060,
    WouldBlock = 10035
}

// milliseconds
int receiveTimeout = 20000;
int sendTimeout = 20000;

public override int Read(byte[] buffer, int offset, int size)
{    
    int startTickCount = Environment.TickCount;
    int received = 0;
    do
    {
        List<Socket> sock = new List<Socket>(new Socket[] {socket});
        Socket.Select(sock, null, null, receiveTimeout*1000 + 1);
        if (Environment.TickCount > startTickCount + receiveTimeout)
            throw new SocketException((int) SocketError.TimedOut);
        try
        {
            received += socket.Receive(buffer, offset + received,
                size - received, SocketFlags.None);
        }
        catch (SocketException ex)
        {
            if (ex.ErrorCode == (int) SocketError.WouldBlock ||
                ex.ErrorCode == (int) SocketError.IOPending ||
                ex.ErrorCode == (int) SocketError.NoBufferSpaceAvailable)
            {
                // socket buffer is probably empty, wait and try again
                Thread.Sleep(30);
            }
            else
                throw; // any serious error occurr
        }
    } while (received < size);
    return received;
}

public override void Write(byte[] buffer, int offset, int size)
{
    int startTickCount = Environment.TickCount;
    int sent = 0;
    do
    {
        List<Socket> sock = new List<Socket>(new Socket[] {socket});
        Socket.Select(null, sock, null, sendTimeout*1000 + 1);
        if (Environment.TickCount > startTickCount + sendTimeout)
            throw new SocketException((int) SocketError.TimedOut);
        try
        {
            sent += socket.Send(buffer, offset + sent,
                size - sent, SocketFlags.None);
        }
        catch (SocketException ex)
        {
            if (ex.ErrorCode == (int) SocketError.WouldBlock ||
                ex.ErrorCode == (int) SocketError.IOPending ||
                ex.ErrorCode == (int) SocketError.NoBufferSpaceAvailable)
            {
                // socket buffer is probably full, wait and try again
                Thread.Sleep(30);
            }
            else
                throw; // any serious error occurr
        }
    } while (sent < size);
}

我发现的例子中缺少的关键因素是Socket.Select(IList checkRead, IList checkWrite, IList checkError, int microSeconds).请记住,此方法可能会修改传递给它的列表(这就是我的代码每次都创建一个新代码的原因),并以微秒而不是毫秒来度量时间.并记住使用Environment.TickCount(这是一个单调的时间源)而不是DateTime.Now测量时间.