从Async Callback调用Sync方法调用？

Question

在异步回调中调用同步方法时会发生什么？

例:

private void AcceptCallback(IAsyncResult AR)
{
    tcp.BeginReceive(ReceiveCallback);
}

private void ReceiveCallback(IAsyncResult AR)
{
    tcp.Send(data);
}

接受连接并启动异步接收回调.当tcp连接接收数据时,它调用接收回调.

如果调用同步Send方法,是否会阻止其他异步回调发生？
或者所有异步回调都是相互独立的？

Answer 1

回调是独立的，因为它们是在线程池 IO 完成工作线程上调用的。

如果您有兴趣，可以在源代码中查看。这个特定的方法适用于Socket类（在内部TcpClient使用UdpClient），其中重叠 IO 用于调用回调（请参阅asyncResult.SetUnmanagedStructures调用顶部的注释：

private void DoBeginReceiveFrom(byte[] buffer, int offset, 
                                int size, SocketFlags socketFlags,
                                EndPoint endPointSnapshot, SocketAddress 
                                socketAddress, OverlappedAsyncResult asyncResult)
{
    EndPoint oldEndPoint = m_RightEndPoint;
    SocketError errorCode = SocketError.SocketError;
    try
    {
        // Set up asyncResult for overlapped WSARecvFrom.
        // This call will use completion ports on WinNT and Overlapped IO on Win9x.
        asyncResult.SetUnmanagedStructures(
                buffer, offset, size, 
                socketAddress, true /* pin remoteEP*/, 
                ref Caches.ReceiveOverlappedCache);

        asyncResult.SocketAddressOriginal = endPointSnapshot.Serialize();

        if (m_RightEndPoint == null) 
        {
            m_RightEndPoint = endPointSnapshot;
        }

        int bytesTransferred;
        errorCode = UnsafeNclNativeMethods.OSSOCK.WSARecvFrom(
            m_Handle,
            ref asyncResult.m_SingleBuffer,
            1,
            out bytesTransferred,
            ref socketFlags,
            asyncResult.GetSocketAddressPtr(),
            asyncResult.GetSocketAddressSizePtr(),
            asyncResult.OverlappedHandle,
            IntPtr.Zero );

        if (errorCode!=SocketError.Success)
        {
            errorCode = (SocketError)Marshal.GetLastWin32Error();
        }
    }
    catch (ObjectDisposedException)
    {
        m_RightEndPoint = oldEndPoint;
        throw;
    }
    finally
    {
        errorCode = asyncResult.CheckAsyncCallOverlappedResult(errorCode);
    }
}