如下所示是设置过程:
Client Server
-------------------- --------------------
| | Sends Requests | |
| Client Socket | -----------------> | Server Socket |
| | <----------------- | |
| | Sends Data | |
-------------------- --------------------
这个过程总是在初始连接时起作用(即新启动的客户端和服务器应用程序)。 客户端可以断开与服务器的连接,这会触发套接字的清理。 重新连接后,我几乎总是(虽然不总是)收到以下错误:
"Receive() - The socket is marked as nonblocking and the receive operation would block"
此错误显示在客户端,并且涉及的套接字是异步、非阻塞套接字。
导致此 SOCKET_ERROR
的行是:
numBytesReceived = theSocket->Receive(theReceiveBuffer, 10000));
where:
- numBytesReceived is an integer (int)
- theSocket is a pointer to a class called CClientSocket which is a specialisation of CASyncSocket, which is part of the MFC C++ Library. This defines the socket object which is embedded within the client. It is an asynchonous, non-blocking socket.
- Receive() is a virtual function within the CASyncSocket object
- theReceiveBuffer is a char array (10000 elements)
在执行上述代码时,该函数返回
SOCKET_ERROR
,并调用theSocket->GetLastError()
返回WSAEWOULDBLOCK
。
SocketTools指出:
当非阻塞(异步)套接字尝试执行无法立即执行的操作时,将返回错误10035。此错误不是致命错误,应由应用程序视为建议性错误。此错误代码对应于Windows套接字错误WSAEWOULDBLOCK。
从非阻塞套接字读取数据时,如果此时没有更多可读取的数据,则会返回此错误。在这种情况下,应用程序应等待OnRead事件触发,表示已有更多数据可供读取。可以使用IsReadable属性确定是否可以从套接字读取数据。
向非阻塞套接字写入数据时,如果本地套接字缓冲区在等待远程主机读取一些数据时被填满,则会返回此错误。当缓冲区空间变得可用时,OnWrite事件将触发,表示可以写入更多数据。可以使用IsWritable属性确定是否可以向套接字写入数据。
需要注意的是,应用程序将不知道可以在单个写操作中发送多少数据,因此,如果客户端尝试过快地发送过多数据,则可能会多次返回此错误。如果在发送数据时频繁出现此错误,可能表示网络延迟较高或远程主机无法快速读取数据。
我一直收到此错误并未能在套接字上接收任何内容。
使用Wireshark,以下通信与源、目的地和TCP位标志发生:
事件:通过TCP/IP连接测试工具到服务器
Client --> Server: SYN
Server --> Client: SYN, ACK
Client --> Server: ACK
This appears to be correct and represents the Three-Way Handshake of connecting.
SocketSniff confirms that a Socket is closed on the client side. It was not possible to get SocketSniff to work with the Windows 10 Server application.
事件:从测试工具发送请求获取数据。
Client --> Server: PSH, ACK
Server --> Client: PSH, ACK
Client --> Server: ACK
Both request data and received data is confirmed to be exchanged successfully
事件:从服务器断开测试工具
Client --> Server: FIN, ACK
Server --> Client: ACK
Server --> Client: FIN, ACK
Client --> Server: ACK
This appears to be correct and represents the Four-Way handshake of connection closure.
SocketSniff confirms that a Socket is closed on the client side. It was not possible to get SocketSniff to work with the Windows 10 Server application.
事件:通过TCP/IP重新连接测试工具到服务器
Client --> Server: SYN
Server --> Client: SYN, ACK
Client --> Server: ACK
This appears to be correct and represents the Three-Way Handshake of connecting.
SocketSniff confirms that a new Socket is opened on the client side. It was not possible to get SocketSniff to work with the Windows 10 Server application.
事件:向测试工具发送数据请求
Client --> Server: PSH, ACK
Server --> Client: ACK
We see no data being pushed (PSH) back to the client, yet we do see an acknowledgement.
有没有人知道这里可能出了什么问题?我知道你们看不到源代码很难进行诊断,但我希望其他人能分享一下遇到这个错误的经验,并指出具体的调查路线。
更多信息:
服务器初始化一个监听线程并绑定到0.0.0.0:49720。'WSAStartup()', 'bind()'和'listen()'函数都返回'0',表示成功。该线程在服务器应用程序的整个生命周期中持续存在。
服务器初始化了两个线程,一个读线程和一个写线程。读线程负责从其套接字读取请求数据,并使用名为Connection的类进行初始化:
HANDLE theConnectionReadThread
= CreateThread(NULL, // Security Attributes
0, // Default Stacksize
Connection::connectionReadThreadHandler, // Callback
(LPVOID)this, // Parameter to pass to thread
CREATE_SUSPENDED, // Don't start yet
NULL); // Don't Save Thread ID
编写线程的初始化方式相似。
在每种情况下,CreateThread()函数返回一个合适的HANDLE,例如:
theConnectionReadThread = 00000570
theConnectionWriteThread = 00000574
实际上,这些线程是在以下函数内部启动的:
void Connection::startThreads()
{
ResumeThread(theConnectionReadThread);
ResumeThread(theConnectionWriteThread);
}
这个函数是从另一个名为
ConnectionManager
的类中调用的,该类管理与服务器的所有可能连接。在这种情况下,我只关心单个连接,以保持简单。将文本输出添加到服务器应用程序后,可以发现在观察到错误行为之前,可以成功地
连接/断开连接
客户端和服务器多次。例如,在connectionReadThreadHandler()
和connectionWriteThreadHandler()
函数中,它们执行时立即向日志文件输出文本。当观察到正确的行为时,以下行会输出到日志文件:
Connection::ResumeThread(theConnectionReadThread) returned 1
Connection::ResumeThread(theConnectionWriteThread) returned 1
ConnectionReadThreadHandler() Beginning
ConnectionWriteThreadHandler() Beginning
如果观察到错误行为,则会将以下行输出到日志文件:
Connection::ResumeThread(theConnectionReadThread) returned 1
Connection::ResumeThread(theConnectionWriteThread) returned 1
回调函数似乎没有被调用。
此时客户端会显示错误,提示:
"Receive() - The socket is marked as nonblocking and the receive operation would block"
在客户端,我有一个名为
CClientDoc
的类,其中包含客户端套接字代码。它首先初始化theSocket
,它是嵌入在客户机中的套接字对象:private:
CClientSocket* theSocket = new CClientSocket;
当客户端和服务器之间初始化连接时,该类会调用一个名为CreateSocket()
的函数,下面是它的一部分代码,以及它调用的辅助函数:
void CClientDoc::CreateSocket()
{
AfxSocketInit();
int lastError;
theSocket->Init(this);
if (theSocket->Create()) // Calls CAyncSocket::Create() (part of afxsock.h)
{
theErrorMessage = "Socket Creation Successful"; // this is a CString
theSocket->SetSocketStatus(WAITING);
}
else
{
// We don't fall in here
}
}
void CClientDoc::Init(CClientDoc* pDoc)
{
pClient = pDoc; // pClient is a pointer to a CClientDoc
}
void CClientDoc::SetSocketStatus(SOCKET_STATUS sock_stat)
{
theSocketStatus = sock_stat; // theSocketStatus is a private member of CClientSocket of type SOCKET_STATUS
}
CreateSocket()
之后立即调用SetupSocket()
,该函数如下:
void CClientDoc::SetupSocket()
{
theSocket->AsyncSelect(); // Function within afxsock.h
}
当客户端与服务器断开连接时,
void CClientDoc::OnClienDisconnect()
{
theSocket->ShutDown(2); // Inline function within afxsock.inl
delete theSocket;
theSocket = new CClientSocket;
CreateSocket();
SetupSocket();
}
因此,我们删除当前的套接字,然后创建一个新的套接字,准备好使用,这似乎按预期工作。
错误信息被写在DoReceive()
函数中的客户端上。该函数调用套接字尝试读取消息。
CClientDoc::DoReceive()
{
int lastError;
switch (numBytesReceived = theSocket->Receive(theReceiveBuffer, 10000))
{
case 0:
// We don't fall in here
break;
case SOCKET_ERROR: // We come in here when the faulty behaviour occurs
if (lastError = theSocket->GetLastError() == WSAEWOULDBLOCK)
{
theErrorMessage = "Receive() - The socket is marked as nonblocking and the receive operation would block";
}
else
{
// We don't fall in here
}
break;
default:
// When connection works, we come in here
break;
}
}
希望这些代码的添加能够提供一些启示。如果需要,我可以再添加一些代码。
谢谢。