我正在将 boost 1.52.0 32 位库与 OpenSSL 32 位库和非托管 Visual C++ 2008 一起用于我正在编写以与现有服务器通信的新客户端。我的测试机器使用的是 Windows 8。我使用的是同步读写。代码内置在一个 DLL 中，可以从 C# 访问，但所有 asio 调用都是在使用 boost::thread_group 创建的非托管线程上完成的。
我发现，当同步读取正在等待数据时，发生在另一个线程中的同步写入似乎被阻塞并且不会退出 - 至少以我编码的方式。所以我的问题是 - 当同步读取正在等待另一个线程中的数据时，是否应该能够完全执行同步写入？
我已经验证，当另一个线程中没有挂起的读取时，我可以成功写出数据。我通过在即将阅读之前冻结正在阅读的线程来做到这一点。然后写的线程写了一条消息。然后我解冻了读取线程，它能够成功地从服务器读取关于已发送消息的响应。
create_thread 方法调用以下方法来处理从服务器的线路读取消息：
void SSLSocket::ProcessServerRequests()
{
// This method is responsible for processing requests from a server.
Byte *pByte;
int ByteCount;
size_t BytesTransferred;
boost::system::error_code Err;
Byte* pReqBuf;
string s;
stringstream ss;
//
try
{
ss << "ProcessServerRequests: Worker thread: " << Logger::NumberToString(boost::this_thread::get_id()) << " started.\n";
Log.LogString(ss.str(), LogInfo);
// Enable the handlers for the handshaking.
IOService->run();
// Wait for the handshake to be sucessfully completed.
do
{
Sleep(50);
} while (!HandShakeReady);
//
sClientIp = pSocket->lowest_layer().remote_endpoint().address().to_string();
uiClientPort = pSocket->lowest_layer().remote_endpoint().port();
ReqAlive = true;
// If the thread that handles sending msgs to all servers has not been created yet, then create that one.
// This thread is created just once to handle all outbound msgs to all servers.
WorkerThreads.create_thread(boost::bind(&SSLSocket::SendWorkerThread));
// Loop until the user quits, or an error is detected. The read method should wait until there is something to read.
do
{
pReqBuf = BufMang.GetPtr(MsgLenBytes);
boost::asio::read(*pSocket, boost::asio::buffer(pReqBuf, MsgLenBytes), boost::asio::transfer_exactly(MsgLenBytes), Err);
if (Err)
{
s = Err.message();
if ((s.find("short r")) == string::npos)
{
ss.str("");
ss << "SSLSocket::ProcessServerRequests: read(1) error = " << Err.message() << "\n. Terminating.\n\n";
Log.LogString(ss.str(), LogError);
}
Terminate();
// Notify the client that an error has been encountered and the program needs to shut down. TBD.
}
else
{
// Get the number of bytes in the message.
pByte = pReqBuf;
B2I.B.B1 = *pByte++;
B2I.B.B2 = *pByte++;
B2I.B.B3 = *pByte++;
B2I.B.B4 = *pByte;
ByteCount = B2I.IntVal;
pReqBuf = BufMang.GetPtr(ByteCount);
// Do a synchronous read which will hang until the entire message is read off the wire.
BytesTransferred = boost::asio::read(*pSocket, boost::asio::buffer(pReqBuf, ByteCount), boost::asio::transfer_exactly(ByteCount), Err);
ss.str("");
ss << "SSLSocket::ProcessServerRequests: # bytes rcvd = " << Logger::NumberToString(BytesTransferred).c_str() << " from ";
ss << sClientIp.c_str() << " : " << Logger::NumberToString(uiClientPort) << "\n";
Log.LogString(ss.str(), LogDebug2);
Log.LogBuf(pReqBuf, (int)BytesTransferred, DisplayInHex, LogDebug3);
if ((Err) || (ByteCount != BytesTransferred))
{
if (Err)
{
ss.str("");
ss << "ProcessServerRequests:read(2) error = " << Err.message() << "\n. Terminating.\n\n";
}
else
{
ss.str("");
ss << "ProcessServerRequests:read(3) error - BytesTransferred (" << Logger::NumberToString(BytesTransferred).c_str() <<
") != ByteCount (" << Logger::NumberToString(ByteCount).c_str() << "). Terminating.\n\n";
}
Log.LogString(ss.str(), LogError);
Terminate();
// Notify the client that an error has been encountered and the program needs to shut down. TBD.
break;
}
// Call the C# callback method that will handle the message.
Log.LogString("SSLSocket::ProcessServerRequests: sending msg to the C# client.\n\n", LogDebug2);
CallbackFunction(this, BytesTransferred, (void*)pReqBuf);
}
} while (ReqAlive);
Log.LogString("SSLSocket::ProcessServerRequests: worker thread done.\n", LogInfo);
}
catch (std::exception& e)
{
stringstream ss;
ss << "SSLSocket::ProcessServerRequests: threw an error - " << e.what() << ".\n";
Log.LogString(ss.str(), LogError);
}
}
create_thread 方法调用以下方法来处理向服务器发送消息：
void SSLSocket::SendWorkerThread()
{
// This method handles sending msgs to the server. It is called upon 1st time class initialization.
//
DWORD WaitResult;
Log.LogString("SSLSocket::SendWorkerThread: Worker thread " + Logger::NumberToString(boost::this_thread::get_id()) + " started.\n", LogInfo);
// Loop until the user quits, or an error of some sort is thrown.
try
{
do
{
// If there are one or more msgs that need to be sent to a server, then send them out.
if (SendMsgQ.Count() > 0)
{
Message* pMsg = SendMsgQ.Pop();
// Byte* pBuf = pMsg->pBuf;
const Byte* pBuf = pMsg->pBuf;
SSLSocket* pSSL = pMsg->pSSL;
int BytesInMsg = pMsg->BytesInMsg;
boost::system::error_code Error;
unsigned int BytesTransferred = boost::asio::write(*pSSL->pSocket, boost::asio::buffer(pBuf, BytesInMsg), Error);
string s = "SSLSocket::SendWorkerThread: # bytes sent = ";
s += Logger::NumberToString(BytesInMsg).c_str();
s += "\n";
Log.LogString(s, LogDebug2);
Log.LogBuf(pBuf, BytesInMsg, DisplayInHex, LogDebug3);
if (Error)
{
Log.LogString("SSLSocket::SendWorkerThread: error sending message - " + Error.message() + "\n", LogError);
}
}
else
{
// Nothing to send, so go into a wait state.
WaitResult = WaitForSingleObject(hEvent, INFINITE);
if (WaitResult != 0L)
{
Log.LogString("SSLSocket::SendWorkerThread: WaitForSingleObject event error. Code = " + Logger::NumberToString(GetLastError()) + ". \n", LogError);
}
}
} while (ReqAlive);
Log.LogString("SSLSocket::SendWorkerThread: Worker thread " + Logger::NumberToString(boost::this_thread::get_id()) + " done.\n", LogInfo);
}
catch (std::exception& e)
{
stringstream ss;
ss << "SSLSocket::SendWorkerThread: threw an error - " << e.what() << ".\n";
Log.LogString(ss.str(), LogError);
}
}
因此，如果在同步读取在另一个线程中挂起时应该能够执行同步写入，那么有人可以告诉我我的代码做错了什么。