[MFC]同步对象——CCriticalSection临界区，CSemaphore信号量

临界区是保证在某一个时间只有一个线程可以访问数据的方法。使用它的过程中，需要给每个线程提供一个共享的临界区对象，无论哪个线程占有临界区对象，都可以访问受到保护的数据，这时候其他的线程需要等待，直至该线程释放临界区对象为止，临界区被释放后，另外的线程可以强占这个临界区，以便访问共享的数据。

临界区对应的一个CCriticalSection对象，当线程需要访问保护数据时，调用临界区对象的Lock()成员函数；当对保护数据的操作完成之后，调用临界区对象的Unlock()成员函数释放临界区对象的拥有权，以使另一个线程可以夺取临界区对象并访问受保护的数据。

// MFCCriticalSectionDlg.h : 头文件 
#pragma once
#define  WM_MSG WM_USER+1
typedef struct THREAD_PARAM
{
	HWND hWnd;
	int nData;
	CCriticalSection* pCriticalSection;
}_THREAD_PARAM;
UINT ThreadFun1(LPVOID pParam);
UINT ThreadFun2(LPVOID pParam);

//MFCCriticalSectionDlg.cpp : 实现文件
CMFCCriticalSectionDlg::CMFCCriticalSectionDlg(CWnd* pParent /*=NULL*/)
	: CDialogEx(CMFCCriticalSectionDlg::IDD, pParent)
{
	m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
	//成员变量
	//	CWinThread* pThread1;
	// 	CWinThread* pThread2;
	// 	THREAD_PARAM mThreadParam;
	pThread1=NULL;
	pThread2=NULL;
	mThreadParam.hWnd=NULL;
	mThreadParam.nData=0;
	mThreadParam.pCriticalSection=new CCriticalSection;
	//存取或者释放一个CCriticalSection对象，要先建立一个CSiingleLock对象，并调用它的Lock和UnLock成员函数。如果CCriticalSection对象是独占使用的，需要调用它的UnLock成员函数以释放对它的占用。或者使用其自身的成员函数Lock()和UnLock()来占有或释放临界区的拥有权。 
}
CMFCCriticalSectionDlg::~CMFCCriticalSectionDlg()
{
	if (pThread1)
	{
		WaitForSingleObject(pThread1->m_hThread,INFINITE);
		delete pThread1;
		pThread1=NULL;
	}
	if (pThread2)
	{
		WaitForSingleObject(pThread2->m_hThread,INFINITE);
		delete pThread2;
		pThread2=NULL;
	}
	if (mThreadParam.pCriticalSection)
	{
		delete mThreadParam.pCriticalSection;
		mThreadParam.pCriticalSection=NULL;
	}
}
//WM_MSG消息函数
LRESULT CMFCCriticalSectionDlg::OnMsgFun(WPARAM wParam,LPARAM lParam)
{
	SetDlgItemInt(IDC_EDIT_DATA,mThreadParam.nData);
	return 0;
}
//启动线程按钮事件
void CMFCCriticalSectionDlg::OnBnClickedButtonStart()
{ 
	if (pThread1)
	{
		DWORD exitCode=0;
		if (::GetExitCodeThread(pThread1->m_hThread,&exitCode))
		{
			if (exitCode == STILL_ACTIVE)
			{
				AfxMessageBox(_T("线程1已经启动。"));
				return;
			}
			else
			{
				delete pThread1;
				pThread1=NULL;
			}
		}
	}
	if (pThread2)
	{
		DWORD exitCode=0;
		if (::GetExitCodeThread(pThread2->m_hThread,&exitCode))
		{
			if (exitCode == STILL_ACTIVE)
			{
				AfxMessageBox(_T("线程2已经启动。"));
				return;
			}
			else
			{
				delete pThread2;
				pThread2=NULL;
			}
		}
	}
	mThreadParam.hWnd=m_hWnd;
	pThread1=AfxBeginThread(ThreadFun1,&mThreadParam,THREAD_PRIORITY_ABOVE_NORMAL,0,CREATE_SUSPENDED); 
	pThread2=AfxBeginThread(ThreadFun2,&mThreadParam,THREAD_PRIORITY_ABOVE_NORMAL,0,CREATE_SUSPENDED);  
	pThread1->m_bAutoDelete=FALSE;
	pThread2->m_bAutoDelete=FALSE;
	pThread1->ResumeThread();
	pThread2->ResumeThread();
}
//线程函数1
UINT ThreadFun1(LPVOID pParam)
{
	THREAD_PARAM* pThreadParam=(THREAD_PARAM*)pParam;
	pThreadParam->pCriticalSection->Lock();
	for (int i=0;i<10;i++)
	{
		pThreadParam->nData++;
		::PostMessage(pThreadParam->hWnd,WM_MSG,0,0);
		Sleep(200);
	}
	pThreadParam->pCriticalSection->Unlock();
	return 0;
}
//线程函数2
UINT ThreadFun2(LPVOID pParam)
{
	THREAD_PARAM* pThreadParam=(THREAD_PARAM*)pParam;
	pThreadParam->pCriticalSection->Lock();
	for (int i=0;i<10;i++)
	{
		pThreadParam->nData--;
		::PostMessage(pThreadParam->hWnd,WM_MSG,0,0);
		Sleep(200);
	}
	pThreadParam->pCriticalSection->Unlock();
	return 0;
}

结果图：

信号量的用法和互斥量的用法很相似，不同的是它可以同一时刻允许多个线程访问同一个资源，创建一个信号量需要用CSemaphore类声明一个对象，一旦创建了一个信号量对象，就可以用它来对资源的访问计数。要实现计数，先创建一个CSingleLock或CMultiLock对象，然后用该对象的Lock()函数减少一个信号量的计数值，Unlock()反之。