SerialPort类源代码分析(有closeport,实践证明可用)

前几篇串口编程大致讲述了Windows下串口的大致操作，接下来分析流行的SerialPort类，它把Windows API封装好，方便开发利用
1、Win32下串口大致操作流程
(1)打开串口：CreateFile函数
(2)建立串口通信事件:CreateEvent函数
(3)初始化串口:SetCommState函数
(4)建立监视线程,即读写数据线程,因为我们不知道什么时候数据会到来,这里是一个异步事件
(5)写数据:WriteFile
(6)结束:关闭线程->停止WaitCommEvent->CloseHandle
2.SerialPort类的数据结构
大致了解操作流程后,先看一下SerialPort类,均在代码注释了
数据成员:
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public:
int m_nWriteSize; //要写入串口的数据大小
HANDLE m_hComm; //串口句柄
protected:
// thread监视线程
CWinThread* m_Thread;
// synchronisation objects
//临界资源
CRITICAL_SECTION m_csCommunicationSync;
//监视线程运行标志
BOOL m_bThreadAlive;
// handles
/*事件句柄*/
HANDLE m_hWriteEvent;
HANDLE m_hShutdownEvent;
// There is a general shutdown when the port is closed.
//事件数组，包括一个写事件，接收事件，关闭事件
HANDLE m_hEventArray[3];
// structures
OVERLAPPED m_ov; //异步I/O模型
COMMTIMEOUTS m_CommTimeouts; //超时设置
DCB m_dcb; //设备控制块
// owner window
CWnd* m_pOwner;
// misc
UINT m_nPortNr;
char* m_szWriteBuffer; //写缓冲区
DWORD m_dwCommEvents; //
DWORD m_nWriteBufferSize; //写缓冲大小
函数成员：
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public:
/*******************Port Operation***********************/
// port initialisation
/*初始化串口*/
BOOL InitPort(CWnd* pPortOwner,
UINT portnr = 1,
UINT baud = 19200,
char parity = 'N',
UINT databits = 8,
UINT stopbits = 1,
DWORD dwCommEvents = EV_RXCHAR,
UINT writebuffersize = 1024);
//关闭端口
void ClosePort();
// start/stop comm watching
//控制串口监视线程
BOOL StartMonitoring(); //开启
BOOL RestartMonitoring(); //复位
BOOL StopMonitoring(); //停止
DWORD GetWriteBufferSize();//获取写缓冲大小
DWORD GetCommEvents(); //获取事件
DCB GetDCB(); //获取DCB
//写数据到串口
void WriteToPort(char* string);
void WriteToPort(char* string,int n);
void WriteToPort(LPCTSTR string);
void WriteToPort(LPCTSTR string,int n);
protected:
/***************** protected memberfunctions **********************/ void ProcessErrorMessage(char* ErrorText);
//线程函数
static UINT CommThread(LPVOID pParam);
//接收字符
static void ReceiveChar(CSerialPort* port, COMSTAT comstat);
//写字符
static void WriteChar(CSerialPort* port);
3.串口操作
(1)初始化串口
流程：检查参数-->检测线程-->创建事件(监视线程)-->打开端口-->设置异步IO结构参数,详细见代码:
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/*初始化串口*/
BOOL CSerialPort::InitPort(CWnd* pPortOwner, // the owner (CWnd) of the port (receives message)
UINT portnr, // portnumber (1..4)
UINT baud, // baudrate
char parity, // parity
UINT databits, // databits
UINT stopbits, // stopbits
DWORD dwCommEvents, // EV_RXCHAR, EV_CTS etc
UINT writebuffersize) // size to the writebuffer
{
assert(portnr > 0 && portnr < 5);
assert(pPortOwner != NULL);
// if the thread is alive: Kill
//线程在的话关断它
if (m_bThreadAlive)
{
do
{
SetEvent(m_hShutdownEvent);
} while (m_bThreadAlive);
TRACE("Thread ended\n");
}
// create events
//创建事件
if (m_ov.hEvent != NULL)
ResetEvent(m_ov.hEvent);
m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hWriteEvent != NULL)
ResetEvent(m_hWriteEvent);
else
m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hShutdownEvent != NULL)
ResetEvent(m_hShutdownEvent);
else
m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
// initialize the event objects
//事件数组初始化，设定优先级别
m_hEventArray[0] = m_hShutdownEvent; // highest priority
m_hEventArray[1] = m_ov.hEvent;
m_hEventArray[2] = m_hWriteEvent;
// initialize critical section
//初始化一个临界资源对象
InitializeCriticalSection(&m_csCommunicationSync);
// set buffersize for writing and save the owner
m_pOwner = pPortOwner;
if (m_szWriteBuffer != NULL)
delete [] m_szWriteBuffer;
m_szWriteBuffer = new char[writebuffersize];
m_nPortNr = portnr;
m_nWriteBufferSize = writebuffersize;
m_dwCommEvents = dwCommEvents;
BOOL bResult = FALSE;
char *szPort = new char[50];
char *szBaud = new char[50];
// now it critical!
/*********************************************
多个线程操作相同的数据时，一般是需要按顺序访问的，否则会引导数据错乱，
无法控制数据，变成随机变量。

为解决这个问题，就需要引入互斥变量，让每个
线程都按顺序地访问变量。

这样就需要使用EnterCriticalSection和LeaveCriticalSection
**********************************************************************/
//进入临界区
EnterCriticalSection(&m_csCommunicationSync);
// if the port is already opened: close it
//端口已经打开的就关闭它
if (m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// prepare port strings
//串口参数
sprintf(szPort, "COM%d", portnr);
sprintf(szBaud, "baud=%d parity=%c data=%d stop=%d", baud, parity, databits, stopbits);
// get a handle to the port
/****************************************************************
*通信程序在CreateFile处指定串口设备及相关的操作属性，再返回一个句柄，
*该句柄将被用于后续的通信操作，并贯穿整个通信过程串口打开后，其属性
*被设置为默认值，根据具体需要，通过调用GetCommState(hComm,&&dcb)读取
*当前串口设备控制块DCB设置，修改后通过SetCommState(hComm,&&dcb)将其写*入。

运用ReadFile()与WriteFile()这两个API函数实现串口读写操作，若为异
*步通信方式，两函数中最后一个参数为指向OVERLAPPED结构的非空指针，在读*写函数返回值为FALSE的情况下，调用GetLastError()函数，返回值为ERROR_IO_PENDING，
*表明I/O操作悬挂，即操作转入后台继续执行。

此时，可以用WaitForSingleObject() *来等待结束信号并设置最长等待时间
*****************************************************************/
m_hComm = CreateFile(szPort, // communication port string (COMX)串口号
GENERIC_READ | GENERIC_WRITE, // read/write types 可以读写
0, // comm devices must be opened with exclusive access独占方式打开串口
NULL, // no security attributes 无安全属性
OPEN_EXISTING, // comm devices must use OPEN_EXISTING
FILE_FLAG_OVERLAPPED, // Async I/O 异步I/O
0); // template must be 0 for comm devices
//如果创建不成功，错误处理
if (m_hComm == INV ALID_HANDLE_V ALUE)
{
// port not found
delete [] szPort;
delete [] szBaud;
return FALSE;
}
// set the timeout values
//设置超时上限(异步IO)
m_CommTimeouts.ReadIntervalTimeout = 1000;
m_CommTimeouts.ReadTotalTimeoutMultiplier = 1000;
m_CommTimeouts.ReadTotalTimeoutConstant = 1000;
m_CommTimeouts.WriteTotalTimeoutMultiplier = 1000;
m_CommTimeouts.WriteTotalTimeoutConstant = 1000;
// configure
/*分别调用Windows API设置串口参数*/
if (SetCommTimeouts(m_hComm, &m_CommTimeouts)) //设置超时
{
/*******************************************************
若对端口数据的响应时间要求较严格，可采用事件驱动方式。

事件驱动方式通过设置事件通知，当所希望的事件发生时，Windows
发出该事件已发生的通知，这与DOS环境下的中断方式很相似。

Windows
定义了9种串口通信事件，较常用的有以下三种：
EV_RXCHAR:接收到一个字节，并放入输入缓冲区；
EV_TXEMPTY:输出缓冲区中的最后一个字符，发送出去；
EV_RXFLAG:接收到事件字符(DCB结构中EvtChar成员)，放入输入缓冲区
在用SetCommMask()指定了有用的事件后，应用程序可调用WaitCommEvent()来等待事
件的发生。

SetCommMask(hComm,0)可使WaitCommEvent()中止。

**************************************************************/
if (SetCommMask(m_hComm, dwCommEvents)) //设置通信事件
{
if (GetCommState(m_hComm, &m_dcb)) //获取当前DCB参数
{
m_dcb.EvtChar = 'q'; //设置字件字符
m_dcb.fRtsControl = RTS_CONTROL_ENABLE; // set RTS bit high!
if (BuildCommDCB(szBaud, &m_dcb)) //填写DCB结构
{
if (SetCommState(m_hComm, &m_dcb)) //配置DCB
; // normal operation... continue
else
ProcessErrorMessage("SetCommState()");
}
else
ProcessErrorMessage("BuildCommDCB()");
}
else
ProcessErrorMessage("GetCommState()");
}
else
ProcessErrorMessage("SetCommMask()");
}
else
ProcessErrorMessage("SetCommTimeouts()");
delete [] szPort;
delete [] szBaud;
// flush the port
//终止读写并清空接收和发送
PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// release critical section
//出临界区
LeaveCriticalSection(&m_csCommunicationSync);
TRACE("Initialisation for communicationport %d completed.\nUse Startmonitor to communicate.\n", portnr);
return TRUE;
}
(2)监视线程的控制
先看比较简单的线程控制吧，主要有开启线程，复位和停止
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//开始监视串口
BOOL CSerialPort::StartMonitoring()
{
if (!(m_Thread = AfxBeginThread(CommThread, this)))
return FALSE;
TRACE("Thread started\n");
return TRUE;
}
//
// Restart the comm thread
//
//重启监视线程（挂起重启）
BOOL CSerialPort::RestartMonitoring()
{
TRACE("Thread resumed\n");
m_Thread->ResumeThread();
return TRUE;
}
//
// Suspend the comm thread
//
//挂起监视线程
BOOL CSerialPort::StopMonitoring()
{
TRACE("Thread suspended\n");
m_Thread->SuspendThread();
return TRUE;
}
(3)监视线程
我们把读写串口的操作全部交给监视线程，现在简单看一下监视线程的大致流程：
检查串口-->进入循环{WaitCommEvent(不阻塞询问)询问事件-->如果有事件来到-->到相应处理(关闭\读\写)}
详细代码如下:
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//监视串口函数
UINT CSerialPort::CommThread(LPVOID pParam)
{
// Cast the void pointer passed to the thread back to
// a pointer of CSerialPort class
CSerialPort *port = (CSerialPort*)pParam;
// Set the status variable in the dialog class to
// TRUE to indicate the thread is running.
port->m_bThreadAlive = TRUE;
// Misc. variables
DWORD BytesTransfered = 0;
DWORD Event = 0;
DWORD CommEvent = 0;
DWORD dwError = 0;
COMSTAT comstat;
BOOL bResult = TRUE;
// Clear comm buffers at startup
//检查串口是否打开
if (port->m_hComm) // check if the port is opened
PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// begin forever loop. This loop will run as long as the thread is alive.
//不断读取数据
for (;;)
{
// Make a call to WaitCommEvent(). This call will return immediatly
// because our port was created as an async port (FILE_FLAG_OVERLAPPED
// and an m_OverlappedStructerlapped structure specified). This call will cause the
// m_OverlappedStructerlapped element m_OverlappedStruct.hEvent, which is part of the m_hEventArray to
// be placed in a non-signeled state if there are no bytes available to be read,
// or to a signeled state if there are bytes available. If this event handle
// is set to the non-signeled state, it will be set to signeled when a
// character arrives at the port.
// we do this for each port!
/********************************************************************
WaitCommEvent函数第3个参数1pOverlapped可以是一个OVERLAPPED结构的变量指针
，也可以是NULL，当用NULL时，表示该函数是同步的，否则表示该函数是异步的。

调用WaitCommEvent时，如果异步操作不能立即完成，会立即返回FALSE，系统
在
WaitCommEvent返回前将OVERLAPPED结构成员hEvent设为无信号状态，等到产生通信
事件时，系统将其置有信号
***********************************************************************/ bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);//表示该函数是异步的
if (!bResult)
{
//如果WaitCommEvent返回Error为NULL，则查询错误信息
// If WaitCommEvent() returns FALSE, process the last error to determin
// the reason..
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING: //正常情况，没有字符可读
{
// This is a normal return value if there are no bytes
// to read at the port.
// Do nothing and continue
break;
}
case 87: //系统错误
{
// Under Windows NT, this value is returned for some reason.
// I have not investigated why, but it is also a valid reply
// Also do nothing and continue.
break;
}
default: //发生其他错误
{
// All other error codes indicate a serious error has
// occured. Process this error.
port->ProcessErrorMessage("WaitCommEvent()");
break;
}
}
}
else //WaitCommEvent()能正确返回
{
// If WaitCommEvent() returns TRUE, check to be sure there are
// actually bytes in the buffer to read.
//
// If you are reading more than one byte at a time from the buffer
// (which this program does not do) you will have the situation occur
// where the first byte to arrive will cause the WaitForMultipleObjects()
// function to stop waiting. The WaitForMultipleObjects() function
// resets the event handle in m_OverlappedStruct.hEvent to the non-signelead state
// as it returns.
//
// If in the time between the reset of this event and the call to
// ReadFile() more bytes arrive, the m_OverlappedStruct.hEvent handle will be set again
// to the signeled state. When the call to ReadFile() occurs, it will
// read all of the bytes from the buffer, and the program will
// loop back around to WaitCommEvent().
//
// At this point you will be in the situation where m_OverlappedStruct.hEvent is set,
// but there are no bytes available to read. If you proceed and call
// ReadFile(), it will return immediatly due to the async port setup, but
// GetOverlappedResults() will not return until the next character arrives.
//
// It is not desirable for the GetOverlappedResults() function to be in
// this state. The thread shutdown event (event 0) and the WriteFile()
// event (Event2) will not work if the thread is blocked by GetOverlappedResults().
//
// The solution to this is to check the buffer with a call to ClearCommError().
// This call will reset the event handle, and if there are no bytes to read
// we can loop back through WaitCommEvent() again, then proceed.
// If there are really bytes to read, do nothing and proceed.
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
if (comstat.cbInQue == 0)
continue;
} // end if bResult
//主等待函数，会阻塞线程
// Main wait function. This function will normally block the thread
// until one of nine events occur that require action.
//等待3个事件：关断/读/写，有一个事件发生就返回
Event = WaitForMultipleObjects(3, //3个事件
port->m_hEventArray,//事件数组
FALSE, //有一个事件发生就返回
INFINITE); //超时时间
switch (Event)
{
case 0:
{
// Shutdown event. This is event zero so it will be
// the higest priority and be serviced first.
//关断事件，关闭串口
CloseHandle(port->m_hComm);
port->m_hComm=NULL;
port->m_bThreadAlive = FALSE;
// Kill this thread. break is not needed, but makes me feel better.
AfxEndThread(100);
break;
}
case 1: // read event 将定义的各种消息发送出去
{
//接收
GetCommMask(port->m_hComm, &CommEvent);
if (CommEvent & EV_RXCHAR)
// Receive character event from port.
ReceiveChar(port, comstat);
if (CommEvent & EV_CTS)
::SendMessage(port->m_pOwner->m_hWnd,
WM_COMM_CTS_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
if (CommEvent & EV_BREAK)
::SendMessage(port->m_pOwner->m_hWnd,
WM_COMM_BREAK_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
if (CommEvent & EV_ERR)
::SendMessage(port->m_pOwner->m_hWnd,
WM_COMM_ERR_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
if (CommEvent & EV_RING)
::SendMessage(port->m_pOwner->m_hWnd,
WM_COMM_RING_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
if (CommEvent & EV_RXFLAG)
::SendMessage(port->m_pOwner->m_hWnd,
WM_COMM_RXFLAG_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
break;
}
case 2: // write event发送数据
{
// Write character event from port
//写
WriteChar(port);
break;
}
} // end switch
} // close forever loop
return 0;
}
(4)读取数据操作
读取数据是一个异步操作，当有数据发来时，会触发读事件m_ov.hEvent，监视线程捕捉到事件后并获知是读事件，进入相关读处理，这里调用函数ReceiveChar
，ReceiveChar中调用ReadFile函数将串口数据读到Buffer缓冲中，相关代码如下：
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//接收数据
void CSerialPort::ReceiveChar(CSerialPort* port, COMSTAT comstat)
{
BOOL bRead = TRUE;
BOOL bResult = TRUE;
DWORD dwError = 0;
DWORD BytesRead = 0;
unsigned char RXBuff;
for (;;)
{
// Gain ownership of the comm port critical section.
// This process guarantees no other part of this program
// is using the port object.
EnterCriticalSection(&port->m_csCommunicationSync);
// ClearCommError() will update the COMSTA T structure and
// clear any other errors.
//更新COMSTA T
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
LeaveCriticalSection(&port->m_csCommunicationSync);
// start forever loop. I use this type of loop because I
// do not know at runtime how many loops this will have to
// run. My solution is to start a forever loop and to
// break out of it when I have processed all of the
// data available. Be careful with this approach and
// be sure your loop will exit.
// My reasons for this are not as clear in this sample
// as it is in my production code, but I have found this
// solutiion to be the most efficient way to do this.
//所有字符均被读出，中断循环
if (comstat.cbInQue == 0)
{
// break out when all bytes have been read
break;
}
EnterCriticalSection(&port->m_csCommunicationSync);
if (bRead)
{
//串口读出，读出缓冲区中字节
bResult = ReadFile(port->m_hComm, // Handle to COMM port
&RXBuff, // RX Buffer Pointer
1, // Read one byte
&BytesRead, // Stores number of bytes read
&port->m_ov); // pointer to the m_ov structure // deal with the error code
//若返回错误，错误处理
if (!bResult)
{
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING:
{
// asynchronous i/o is still in progress
// Proceed on to GetOverlappedResults();
//异步IO仍在进行
bRead = FALSE;
break;
}
default:
{ //其他错误处理
// Another error has occured. Process this error.
port->ProcessErrorMessage("ReadFile()");
break;
}
}
}
else
{ //ReadFile返回TRUE
// ReadFile() returned complete. It is not necessary to call GetOverlappedResults()
bRead = TRUE;
}
} // close if (bRead)
//异步IO操作仍在进行，需要调用GetOverlappedResult查询
if (!bRead)
{
bRead = TRUE;
bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port
&port->m_ov, // Overlapped structure
&BytesRead, // Stores number of bytes read
TRUE); // Wait flag
// deal with the error code
if (!bResult)
{
port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()");
}
} // close if (!bRead)
LeaveCriticalSection(&port->m_csCommunicationSync);
// notify parent that a byte was received
::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM) RXBuff, (LPARAM) port->m_nPortNr);
} // end forever loop
}
(5)写数据
也是由监视线程操作，不过触发事件交给主线程来触发，函数是WriteToPort
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//
// Write a string to the port
//
void CSerialPort::WriteToPort(char* string)
{
assert(m_hComm != 0);
//写进写缓冲区
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
strcpy(m_szWriteBuffer, string);
m_nWriteSize=strlen(string);
// set event for write
SetEvent(m_hWriteEvent);
}
线程调用的函数WriteChar，把缓冲里的数据写到串口中，期间调用WriteFile
详细代码：
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//写数据
void CSerialPort::WriteChar(CSerialPort* port)
{
BOOL bWrite = TRUE;
BOOL bResult = TRUE;
DWORD BytesSent = 0;
ResetEvent(port->m_hWriteEvent); //复位写事件句柄
// Gain ownership of the critical section
EnterCriticalSection(&port->m_csCommunicationSync);
if (bWrite)
{
// Initailize variables
port->m_ov.Offset = 0;
port->m_ov.OffsetHigh = 0;
// Clear buffer
PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
//串口写入
bResult = WriteFile(port->m_hComm, // Handle to COMM Port
port->m_szWriteBuffer, // Pointer to message buffer in calling finction
// strlen((char*)port->m_szWriteBuffer), // Length of message to send
port->m_nWriteSize, // Length of message to send
&BytesSent, // Where to store the number of bytes sent
&port->m_ov); // Overlapped structure
// deal with any error codes
if (!bResult)
{
DWORD dwError = GetLastError();
switch (dwError)
{
case ERROR_IO_PENDING:
{
// continue to GetOverlappedResults()
BytesSent = 0;
bWrite = FALSE;
break;
}
default:
{
// all other error codes
port->ProcessErrorMessage("WriteFile()");
}
}
}
else
{
LeaveCriticalSection(&port->m_csCommunicationSync);
}
} // end if(bWrite)
if (!bWrite)
{
bWrite = TRUE;
bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port
&port->m_ov, // Overlapped structure
&BytesSent, // Stores number of bytes sent
TRUE); // Wait flag
LeaveCriticalSection(&port->m_csCommunicationSync);
// deal with the error code
// if (!bResult)
{
// port->ProcessErrorMessage("GetOverlappedResults() in WriteFile()");
}
} // end if (!bWrite)
//Verify that the data size send equals what we tried to send
if (BytesSent != port->m_nWriteSize) // Length of message to send)
{
TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n", BytesSent, strlen((char*)port->m_szWriteBuffer));
}
// ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_TXEMPTY_DETECTED, (WPARAM) RXBuff, (LPARAM) port->m_nPortNr);
// ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_TXEMPTY_DETECTED,0,(LPARAM) port->m_nPortNr);
}
(6)其他操作
其他比如获取DCB，关闭等，比较简单，不做分析
代码如下：
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//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
return m_dcb;
}
//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
return m_dwCommEvents;
}
//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
return m_nWriteBufferSize;
}
//修改了多次ClosePort()函数，最终确定以下方式，可以很好执行关闭void CSerialPort::ClosePort()
{
while (m_bThreadAlive)
{
SetCommMask(m_hComm, 0);
SetEvent(m_hShutdownEvent);
}
if (m_ov.hEvent)
{
CloseHandle(m_ov.hEvent);
}
if (m_hWriteEvent)
{
CloseHandle(m_hWriteEvent);
}
if (m_hShutdownEvent)
{
CloseHandle(m_hShutdownEvent);
}
m_ov.hEvent = NULL;
m_hWriteEvent = NULL;
m_hShutdownEvent = NULL;
if (m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
}。