深入浅出Win32多线程措施设计综合实例
副标题#e#
本章我们将以家产节制和嵌入式系统中运用极为遍及的串口通信为例报告多线程的典范应用。
而网络通信也是多线程应用最遍及的规模之一，所以本章的最后一节也将对多线程网络通信举办简短的描写。
1.串口通信
在家产节制系统中，工控机（一般都基于PC Windows平台）常常需要与单片机通过串口举办通信。因此，操纵和利用PC的串口成为大大都单片机、嵌入式系统规模工程师必需具备的本领。
串口的利用需要通过三个步调来完成的：
（1） 打开通信端口；
（2） 初始化串口，配置波特率、数据位、遏制位、奇偶校验等参数。为了给读者一个直观的印象，下图从Windows的"节制面板－>系统－>设备打点器－>通信端口（COM1）"打开COM的配置窗口：
（3） 读写串口。
在WIN32平台下，对通信端口举办操纵跟根基的文件操纵一样。
建设/打开COM资源
下列函数假如挪用乐成，则返回一个标识通信端口的句柄，不然返回-1：
HADLE CreateFile(PCTSTR lpFileName, //通信端口名，如"COM1"
WORD dwDesiredAccess, //对资源的会见范例
WORD dwShareMode, //指定共享模式，COM不能共享，该参数为0
PSECURITY_ATTRIBUTES lpSecurityAttributes,
//安详描写符指针，可为NULL
WORD dwCreationDisposition, //建设方法
WORD dwFlagsAndAttributes, //文件属性，可为NULL
HANDLE hTemplateFile //模板文件句柄，置为NULL
);
得到/配置COM属性
下列函数可以得到COM口的设备节制块，从而得到相关参数：
BOOL WINAPI GetCommState(
HANDLE hFile, //标识通信端口的句柄
LPDCB lpDCB //指向一个设备节制块(DCB布局)的指针
);
假如要调解通信端口的参数，则需要从头设置设备节制块，再用WIN32 API SetCommState()函数举办配置：
BOOL SetCommState(
HANDLE hFile, //标识通信端口的句柄
LPDCB lpDCB //指向一个设备节制块(DCB布局)的指针
);
#p#副标题#e#
DCB布局包括了串口的各项参数配置，如下：
typedef struct _DCB
{
// dcb
DWORD DCBlength; // sizeof(DCB)
DWORD BaudRate; // current baud rate
DWORD fBinary: 1; // binary mode, no EOF check
DWORD fParity: 1; // enable parity checking
DWORD fOutxCtsFlow: 1; // CTS output flow control
DWORD fOutxDsrFlow: 1; // DSR output flow control
DWORD fDtrControl: 2; // DTR flow control type
DWORD fDsrSensitivity: 1; // DSR sensitivity
DWORD fTXContinueOnXoff: 1; // XOFF continues Tx
DWORD fOutX: 1; // XON/XOFF out flow control
DWORD fInX: 1; // XON/XOFF in flow control
DWORD fErrorChar: 1; // enable error replacement
DWORD fNull: 1; // enable null stripping
DWORD fRtsControl: 2; // RTS flow control
DWORD fAbortOnError: 1; // abort reads/writes on error
DWORD fDummy2: 17; // reserved
WORD wReserved; // not currently used
WORD XonLim; // transmit XON threshold
WORD XoffLim; // transmit XOFF threshold
BYTE ByteSize; // number of bits/byte, 4-8
BYTE Parity; // 0-4=no,odd,even,mark,space
BYTE StopBits; // 0,1,2 = 1, 1.5, 2
char XonChar; // Tx and Rx XON character
char XoffChar; // Tx and Rx XOFF character
char ErrorChar; // error replacement character
char EofChar; // end of input character
char EvtChar; // received event character
WORD wReserved1; // reserved; do not use
} DCB;
读写串口
在读写串口之前，还要用PurgeComm()函数清空缓冲区，并用SetCommMask ()函数配置事件掩模来监督指定通信端口上的事件，其原型为：
BOOL SetCommMask(
HANDLE hFile, //标识通信端口的句柄
DWORD dwEvtMask //可以或许使能的通信事件
);
串口上大概产生的事件如下表所示：
| 值 | 事件描写 |
| EV_BREAK | A break was detected on input. |
| EV_CTS | The CTS (clear-to-send) signal changed state. |
| EV_DSR | The DSR(data-set-ready) signal changed state. |
| EV_ERR | A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY. |
| EV_RING | A ring indicator was detected. |
| EV_RLSD | The RLSD (receive-line-signal-detect) signal changed state. |
| EV_RXCHAR | A character was received and placed in the input buffer. |
| EV_RXFLAG | The event character was received and placed in the input buffer. The event character is specified in the device’s DCB structure, which is applied to a serial port by using the SetCommState function. |
| EV_TXEMPTY | The last character in the output buffer was sent. |
在配置功德件掩模后，我们就可以操作WaitCommEvent()函数来期待串口上产闹事件，其函数原型为：
#p#分页标题#e#
BOOL WaitCommEvent(
HANDLE hFile, //标识通信端口的句柄
LPDWORD lpEvtMask, //指向存放事件标识变量的指针
LPOVERLAPPED lpOverlapped, // 指向overlapped布局
);
我们可以在产闹事件后，按拍照应的事件范例，举办串口的读写操纵：
BOOL ReadFile(HANDLE hFile, //标识通信端口的句柄
LPVOID lpBuffer, //输入数据Buffer指针
DWORD nNumberOfBytesToRead, // 需要读取的字节数
LPDWORD lpNumberOfBytesRead, //实际读取的字节数指针
LPOVERLAPPED lpOverlapped //指向overlapped布局
);
BOOL WriteFile(HANDLE hFile, //标识通信端口的句柄
LPCVOID lpBuffer, //输出数据Buffer指针
DWORD nNumberOfBytesToWrite, //需要写的字节数
LPDWORD lpNumberOfBytesWritten, //实际写入的字节数指针
LPOVERLAPPED lpOverlapped //指向overlapped布局
);
2.工程实例
下面我们用第1节所述API实现一个多线程的串口通信措施。这个例子工程（工程名为MultiThreadCom）的界面很简朴，如下图所示：
它是一个多线程的应用措施，包罗两个事情者线程，别离处理惩罚串口1和串口2。为了简化问题，我们让毗连两个串口的电缆只包括RX、TX两根连线（即不以硬件节制RS-232，串口上只会产生EV_TXEMPTY、EV_RXCHAR事件）。
在工程实例的BOOL CMultiThreadComApp::InitInstance()函数中，启动并配置COM1和COM2，其源代码为：
BOOL CMultiThreadComApp::InitInstance()
{
AfxEnableControlContainer();
//打开并配置COM1
hComm1=CreateFile("COM1", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
if (hComm1==(HANDLE)-1)
{
AfxMessageBox("打开COM1失败");
return false;
}
else
{
DCB wdcb;
GetCommState (hComm1,&wdcb);
wdcb.BaudRate=9600;
SetCommState (hComm1,&wdcb);
PurgeComm(hComm1,PURGE_TXCLEAR);
}
//打开并配置COM2
hComm2=CreateFile("COM2", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
if (hComm2==(HANDLE)-1)
{
AfxMessageBox("打开COM2失败");
return false;
}
else
{
DCB wdcb;
GetCommState (hComm2,&wdcb);
wdcb.BaudRate=9600;
SetCommState (hComm2,&wdcb);
PurgeComm(hComm2,PURGE_TXCLEAR);
}
CMultiThreadComDlg dlg;
m_pMainWnd = &dlg;
int nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}
return FALSE;
}
从此我们在对话框CMultiThreadComDlg的初始化函数OnInitDialog中启动两个体离处理惩罚COM1和COM2的线程：
BOOL CMultiThreadComDlg::OnInitDialog()
{
CDialog::OnInitDialog();
// Add "About..." menu item to system menu.
// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);
CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
}
// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon
// TODO: Add extra initialization here
//启动串口1处理惩罚线程
DWORD nThreadId1;
hCommThread1 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com1ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId1);
if (hCommThread1 == NULL)
{
AfxMessageBox("建设串口1处理惩罚线程失败");
return false;
}
//启动串口2处理惩罚线程
DWORD nThreadId2;
hCommThread2 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com2ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId2);
if (hCommThread2 == NULL)
{
AfxMessageBox("建设串口2处理惩罚线程失败");
return false;
}
return TRUE; // return TRUE unless you set the focus to a control
}
两个串口COM1和COM2对应的线程处理惩罚函数期待串口上产闹事件，并按照事件范例和自身缓冲区是否有数据要发送举办相应的处理惩罚，其源代码为：
#p#分页标题#e#
DWORD WINAPI Com1ThreadProcess(HWND hWnd//主窗口句柄)
{
DWORD wEven;
char str[10]; //读入数据
SetCommMask(hComm1, EV_RXCHAR | EV_TXEMPTY);
while (TRUE)
{
WaitCommEvent(hComm1, &wEven, NULL);
if(wEven = 0)
{
CloseHandle(hCommThread1);
hCommThread1 = NULL;
ExitThread(0);
}
else
{
switch (wEven)
{
case EV_TXEMPTY:
if (wTxPos < wTxLen)
{
//在串口1写入数据
DWORD wCount; //写入的字节数
WriteFile(hComm1, com1Data.TxBuf[wTxPos], 1, &wCount, NULL);
com1Data.wTxPos++;
}
break;
case EV_RXCHAR:
if (com1Data.wRxPos < com1Data.wRxLen)
{
//读取串口数据, 处理惩罚收到的数据
DWORD wCount; //读取的字节数
ReadFile(hComm1, com1Data.RxBuf[wRxPos], 1, &wCount, NULL);
com1Data.wRxPos++;
if(com1Data.wRxPos== com1Data.wRxLen);
::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
}
break;
}
}
}
}
return TRUE;
}
DWORD WINAPI Com2ThreadProcess(HWND hWnd //主窗口句柄)
{
DWORD wEven;
char str[10]; //读入数据
SetCommMask(hComm2, EV_RXCHAR | EV_TXEMPTY);
while (TRUE)
{
WaitCommEvent(hComm2, &wEven, NULL);
if (wEven = 0)
{
CloseHandle(hCommThread2);
hCommThread2 = NULL;
ExitThread(0);
}
else
{
switch (wEven)
{
case EV_TXEMPTY:
if (wTxPos < wTxLen)
{
//在串口2写入数据
DWORD wCount; //写入的字节数
WriteFile(hComm2, com2Data.TxBuf[wTxPos], 1, &wCount, NULL);
com2Data.wTxPos++;
}
break;
case EV_RXCHAR:
if (com2Data.wRxPos < com2Data.wRxLen)
{
//读取串口数据, 处理惩罚收到的数据
DWORD wCount; //读取的字节数
ReadFile(hComm2, com2Data.RxBuf[wRxPos], 1, &wCount, NULL);
com2Data.wRxPos++;
if(com2Data.wRxPos== com2Data.wRxLen);
::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
}
break;
}
}
}
return TRUE;
}
线程节制函数中所操纵的com1Data和com2Data是与串口对应的数据布局struct tagSerialPort的实例，这个数据布局是：
typedef struct tagSerialPort
{
BYTE RxBuf[SPRX_BUFLEN];//吸收Buffer
WORD wRxPos; //当前吸收字节位置
WORD wRxLen; //要吸收的字节数
BYTE TxBuf[SPTX_BUFLEN];//发送Buffer
WORD wTxPos; //当前发送字节位置
WORD wTxLen; //要发送的字节数
}SerialPort, * LPSerialPort;
3.多线程串口类
#p#分页标题#e#
利用多线程串口通信更利便的途径是编写一个多线程的串口类，譬喻Remon Spekreijse编写了一个CSerialPort串口类。仔细阐明这个类的源代码，将十分有助于我们对先前所学多线程及同步常识的领略。
3.1类的界说
#ifndef __SERIALPORT_H__
#define __SERIALPORT_H__
#define WM_COMM_BREAK_DETECTED WM_USER+1 // A break was detected on input.
#define WM_COMM_CTS_DETECTED WM_USER+2 // The CTS (clear-to-send) signal changed state.
#define WM_COMM_DSR_DETECTED WM_USER+3 // The DSR (data-set-ready) signal changed state.
#define WM_COMM_ERR_DETECTED WM_USER+4 // A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.
#define WM_COMM_RING_DETECTED WM_USER+5 // A ring indicator was detected.
#define WM_COMM_RLSD_DETECTED WM_USER+6 // The RLSD (receive-line-signal-detect) signal changed state.
#define WM_COMM_RXCHAR WM_USER+7 // A character was received and placed in the input buffer.
#define WM_COMM_RXFLAG_DETECTED WM_USER+8 // The event character was received and placed in the input buffer.
#define WM_COMM_TXEMPTY_DETECTED WM_USER+9 // The last character in the output buffer was sent.
class CSerialPort
{
public:
// contruction and destruction
CSerialPort();
virtual ~CSerialPort();
// port initialisation
BOOL InitPort(CWnd* pPortOwner, UINT portnr = 1, UINT baud = 19200, char parity = 'N', UINT databits = 8, UINT stopsbits = 1, DWORD dwCommEvents = EV_RXCHAR | EV_CTS, UINT nBufferSize = 512);
// start/stop comm watching
BOOL StartMonitoring();
BOOL RestartMonitoring();
BOOL StopMonitoring();
DWORD GetWriteBufferSize();
DWORD GetCommEvents();
DCB GetDCB();
void WriteToPort(char* string);
protected:
// protected memberfunctions
void ProcessErrorMessage(char* ErrorText);
static UINT CommThread(LPVOID pParam);
static void ReceiveChar(CSerialPort* port, COMSTAT comstat);
static void WriteChar(CSerialPort* port);
// thread
CWinThread* m_Thread;
// synchronisation objects
CRITICAL_SECTION m_csCommunicationSync;
BOOL m_bThreadAlive;
// handles
HANDLE m_hShutdownEvent;
HANDLE m_hComm;
HANDLE m_hWriteEvent;
// Event array.
// One element is used for each event. There are two event handles for each port.
// A Write event and a receive character event which is located in the overlapped structure (m_ov.hEvent).
// There is a general shutdown when the port is closed.
HANDLE m_hEventArray[3];
// structures
OVERLAPPED m_ov;
COMMTIMEOUTS m_CommTimeouts;
DCB m_dcb;
// owner window
CWnd* m_pOwner;
// misc
UINT m_nPortNr;
char* m_szWriteBuffer;
DWORD m_dwCommEvents;
DWORD m_nWriteBufferSize;
};
#endif __SERIALPORT_H__
3.2类的实现
3.2.1结构函数与析构函数
举办相关变量的赋初值及内存规复：
CSerialPort::CSerialPort()
{
m_hComm = NULL;
// initialize overlapped structure members to zero
m_ov.Offset = 0;
m_ov.OffsetHigh = 0;
// create events
m_ov.hEvent = NULL;
m_hWriteEvent = NULL;
m_hShutdownEvent = NULL;
m_szWriteBuffer = NULL;
m_bThreadAlive = FALSE;
}
//
// Delete dynamic memory
//
CSerialPort::~CSerialPort()
{
do
{
SetEvent(m_hShutdownEvent);
}
while (m_bThreadAlive);
TRACE("Thread ended\n");
delete []m_szWriteBuffer;
}
3.2.2焦点函数：初始化串口
在初始化串口函数中，将打开串口，配置相关参数，并建设串口相关的用户节制事件，初始化临界区（Critical Section），以成队的EnterCriticalSection()、LeaveCriticalSection()函数举办资源的排它性会见：
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
if (m_bThreadAlive)
{
do
{
SetEvent(m_hShutdownEvent);
}
while (m_bThreadAlive);
TRACE("Thread ended\n");
}
// create events
if (m_ov.hEvent != NULL)
ResetEvent(m_ov.hEvent);
m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hWriteEvent != NULL)
ResetEvent(m_hWriteEvent);
m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hShutdownEvent != NULL)
ResetEvent(m_hShutdownEvent);
m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
// initialize the event objects
m_hEventArray[0] = m_hShutdownEvent; // highest priority
m_hEventArray[1] = m_ov.hEvent;
m_hEventArray[2] = m_hWriteEvent;
// initialize critical section
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!
EnterCriticalSection(&m_csCommunicationSync);
// if the port is already opened: close it
if (m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// prepare port strings
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
m_hComm = CreateFile(szPort, // communication port string (COMX)
GENERIC_READ | GENERIC_WRITE, // read/write types
0, // comm devices must be opened with exclusive access
NULL, // no security attributes
OPEN_EXISTING, // comm devices must use OPEN_EXISTING
FILE_FLAG_OVERLAPPED, // Async I/O
0); // template must be 0 for comm devices
if (m_hComm == INVALID_HANDLE_VALUE)
{
// port not found
delete []szPort;
delete []szBaud;
return FALSE;
}
// set the timeout values
m_CommTimeouts.ReadIntervalTimeout = 1000;
m_CommTimeouts.ReadTotalTimeoutMultiplier = 1000;
m_CommTimeouts.ReadTotalTimeoutConstant = 1000;
m_CommTimeouts.WriteTotalTimeoutMultiplier = 1000;
m_CommTimeouts.WriteTotalTimeoutConstant = 1000;
// configure
if (SetCommTimeouts(m_hComm, &m_CommTimeouts))
{
if (SetCommMask(m_hComm, dwCommEvents))
{
if (GetCommState(m_hComm, &m_dcb))
{
m_dcb.fRtsControl = RTS_CONTROL_ENABLE; // set RTS bit high!
if (BuildCommDCB(szBaud, &m_dcb))
{
if (SetCommState(m_hComm, &m_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
PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// release critical section
LeaveCriticalSection(&m_csCommunicationSync);
TRACE("Initialisation for communicationport %d completed.\nUse Startmonitor to communicate.\n", portnr);
return TRUE;
}
3.3.3焦点函数：串口线程节制函数
串口线程处理惩罚函数是整个类中最焦点的部门，它主要完成两类事情：
（1）操作WaitCommEvent函数对串口上产生的事件举办获取并按照事件的差异范例举办相应的处理惩罚；
（2）操作WaitForMultipleObjects函数对串口相关的用户节制事件举办期待并做相应处理惩罚。
#p#分页标题#e#
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
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.
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!
bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);
if (!bResult)
{
// If WaitCommEvent() returns FALSE, process the last error to determin
// the reason..
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING:
{
// This is a normal return value if there are no bytes
// to read at the port.
// Do nothing and continue
break;
}
case 87:
{
// 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:
{
// All other error codes indicate a serious error has
// occured. Process this error.
port->ProcessErrorMessage("WaitCommEvent()");
break;
}
}
}
else
{
// 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
// Main wait function. This function will normally block the thread
// until one of nine events occur that require action.
Event = WaitForMultipleObjects(3, port->m_hEventArray, FALSE, INFINITE);
switch (Event)
{
case 0:
{
// Shutdown event. This is event zero so it will be
// the higest priority and be serviced first.
port->m_bThreadAlive = FALSE;
// Kill this thread. break is not needed, but makes me feel better.
AfxEndThread(100);
break;
}
case 1:
// read event
{
GetCommMask(port->m_hComm, &CommEvent);
if (CommEvent &EV_CTS)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_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);
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_RXCHAR)
// Receive character event from port.
ReceiveChar(port, comstat);
break;
}
case 2:
// write event
{
// Write character event from port
WriteChar(port);
break;
}
} // end switch
} // close forever loop
return 0;
}
下列三个函数用于对串口线程举办启动、挂起和规复：
#p#分页标题#e#
//
// start comm watching
//
BOOL CSerialPort::StartMonitoring()
{
if (!(m_Thread = AfxBeginThread(CommThread, this)))
return FALSE;
TRACE("Thread started\n");
return TRUE;
}
//
// Restart the comm thread
//
BOOL CSerialPort::RestartMonitoring()
{
TRACE("Thread resumed\n");
m_Thread->ResumeThread();
return TRUE;
}
//
// Suspend the comm thread
//
BOOL CSerialPort::StopMonitoring()
{
TRACE("Thread suspended\n");
m_Thread->SuspendThread();
return TRUE;
}
3.3.4读写串口
下面一组函数是用户对串口举办读写操纵的接口：
#p#分页标题#e#
//
// Write a character.
//
void CSerialPort::WriteChar(CSerialPort *port)
{
BOOL bWrite = TRUE;
BOOL bResult = TRUE;
DWORD BytesSent = 0;
ResetEvent(port->m_hWriteEvent);
// 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);
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
&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 != strlen((char*)port->m_szWriteBuffer))
{
TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n",
BytesSent, strlen((char*)port->m_szWriteBuffer));
}
}
//
// Character received. Inform the owner
//
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 COMSTAT structure and
// clear any other errors.
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.
if (comstat.cbInQue == 0)
{
// break out when all bytes have been read
break;
}
EnterCriticalSection(&port->m_csCommunicationSync);
if (bRead)
{
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
if (!bResult)
{
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING:
{
// asynchronous i/o is still in progress
// Proceed on to GetOverlappedResults();
bRead = FALSE;
break;
}
default:
{
// Another error has occured. Process this error.
port->ProcessErrorMessage("ReadFile()");
break;
}
}
}
else
{
// ReadFile() returned complete. It is not necessary to call GetOverlappedResults()
bRead = TRUE;
}
} // close if (bRead)
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
}
//
// Write a string to the port
//
void CSerialPort::WriteToPort(char *string)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
strcpy(m_szWriteBuffer, string);
// set event for write
SetEvent(m_hWriteEvent);
}
//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
return m_nWriteBufferSize;
}
3.3.5节制接口
应用措施员利用下列一组public函数可以获取串口的DCB及串口上产生的事件：
#p#分页标题#e#
//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
return m_dcb;
}
//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
return m_dwCommEvents;
}
3.3.6错误处理惩罚
#p#分页标题#e#
//
// If there is a error, give the right message
//
void CSerialPort::ProcessErrorMessage(char *ErrorText)
{
char *Temp = new char[200];
LPVOID lpMsgBuf;
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
NULL, GetLastError(), MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
// Default language
(LPTSTR) &lpMsgBuf, 0, NULL);
sprintf(Temp,
"WARNING: %s Failed with the following error:\n%s\nPort: %d\n", (char*)
ErrorText, lpMsgBuf, m_nPortNr);
MessageBox(NULL, Temp, "Application Error", MB_ICONSTOP);
LocalFree(lpMsgBuf);
delete []Temp;
}
仔细阐明Remon Spekreijse的CSerialPort类对我们领略多线程及其同步机制是大有益处的，从http://codeguru.earthweb.com/network/serialport.shtml我们可以获取CSerialPort类的先容与工程实例。别的，电子家产出书社《Visual C++/Turbo C串口通信编程实践》一书的作者龚建伟也编写了一个利用CSerialPort类的例子，可以从http://www.gjwtech.com/scomm/sc2serialportclass.htm得到详情。
4.多线程网络通信
在网络通信中利用多线程主要有两种途径，即主监控线程和线程池。
4.1主监控线程
这种方法指的是措施中利用一个主线程监控某特定端口，一旦在这个端口上产生毗连请求，则主监控线程动态利用CreateThread派生出新的子线程处理惩罚该请求。主线程在派生子线程后不再对子线程加以节制和调治，而由子线程独自和客户方产生毗连并处理惩罚异常。
利用这种要领的利益是：
（1）可以较快地实现原型设计，尤其在用户数目较少、毗连保持时间较长时有表示较好；
（2）主线程不与子线程产生通信，在必然水平上淘汰了系统资源的耗损。
其缺点是：
（1）生成和终止子线程的开销较量大；
（2）对远端用户的节制较弱。
这种多线程方法总的特点是"动态生成，静态调治"。
4.2线程池
这种方法指的是主线程在初始化时静态地生成必然数量的悬挂子线程，安排于线程池中。随后，主线程将对这些悬挂子线程进动作态调治。一旦客户发出毗连请求，主线程将从线程池中查找一个悬挂的子线程：
（1）假如找到，主线程将该毗连分派给这个被发明的子线程。子线程从主线程处经受该毗连，并与用户通信。当毗连竣事时，该子线程将自动悬挂，并进人线程池期待再次被调治；
（2）假如当前已没有可用的子线程，主线程将告示提倡毗连的客户。
利用这种要领举办设计的利益是：
（1）主线程可以更好地对派生的子线程举办节制和调治；
（2）对长途用户的监控和打点本领较强。
固然主线程对子线程的调治要耗损必然的资源，可是与主监控线程方法中派生和终止线程所要淹灭的资源对比，要少许多。因此，利用该种要领设计和实现的系统在客户端毗连和终止改观频繁时有上佳表示。
这种多线程方法总的特点是"静态生成，动态调治"。
