2023年6月22日发(作者：)

对于EnterCriticalSection和LeaveCriticalSection的理解和⽤法线程锁的概念函数EnterCriticalSection和LeaveCriticalSection的⽤法注：使⽤结构CRITICAL_SECTION 需加⼊头⽂件#include “afxmt.h”定义⼀个全局的锁 CRITICAL_SECTION的实例和⼀个静态全局变量1. CRITICAL_SECTIONcs;// 临界区的声明2. static intn_AddValue = 0;//定义⼀个静态的全部变量n_AddValue创建两个线程函数，代码实现如下：1. //第⼀个线程2. UINT FirstThread(LPVOIDlParam)3. {4. EnterCriticalSection(&cs);//进⼊临界区，对需要保护的资源进⾏操作5. for(int i =0; i<10;i++){

6. n_AddValue ++;7. cout <<"n_AddValue in FirstThread is"<

8.

9. }10. LeaveCriticalSection(&cs);//离开临界区

11. return 0;12.

13. }14.

15. //第⼆个线程16. UINT SecondThread(LPVOIDlParam)17. {18. EnterCriticalSection(&cs);//进⼊临界区19. for(int i =0; i<10;i++){

20. n_AddValue ++;

21. cout <<"n_AddValue in SecondThread is"<

22.

23. }24. LeaveCriticalSection(&cs);//离开临界区25.

26. return 0;27.

28. }在主函数添加以下代码1. int_tmain(intargc, TCHAR*argv[],TCHAR* envp[])2. {3. int nRetCode =0;4.

5. // 初始化 MFC 并在失败时显⽰错误6. if (!AfxWinInit(::GetModuleHandle(NULL),NULL, ::GetCommandLine(),0))7. {8. // TODO: 更改错误代码以符合您的需要9. _tprintf(_T("错误: MFC 初始化失败/n"));10. nRetCode =1;11. }12. else13. {14.

15. InitializeCriticalSection(&cs);//初始化临界区16.

17.

18. CWinThread *pFirstThread,*pSecondThread;//存储函数AfxBeginThread返回的CWinThread指针19.

20.

21. pFirstThread =AfxBeginThread(FirstThread,LPVOID(NULL));//启动第⼀个线程22. pSecondThread =AfxBeginThread(SecondThread,LPVOID(NULL));//启动第⼆个线程23.

24. HANDLE hThreadHandle[2];//25. hThreadHandle[0] =pFirstThread->m_hThread;26. hThreadHandle[1] =pSecondThread->m_hThread;27.

28. //等待线程返回29. WaitForMultipleObjects(2,hThreadHandle,TRUE,INFINITE);

30. }31.

32. return nRetCode;33. }输出：n_AddValue in FirstThread is 1n_AddValue in FirstThread is 2n_AddValue in FirstThread is 3n_AddValue in FirstThread is 4n_AddValue in FirstThread is 5n_AddValue in FirstThread is 6n_AddValue in FirstThread is 7n_AddValue in FirstThread is 8n_AddValue in FirstThread is 9n_AddValue in FirstThread is 10n_AddValue in SecondThread is 11n_AddValue in SecondThread is 12n_AddValue in SecondThread is 13n_AddValue in SecondThread is 14n_AddValue in SecondThread is 15n_AddValue in SecondThread is 16n_AddValue in SecondThread is 17n_AddValue in SecondThread is 18n_AddValue in SecondThread is 19n_AddValue in SecondThread is 20如果把两个线程函数中的EnterCriticalSection和LeaveCriticalSection位置移到for循环中去，线程的执⾏顺序将会改变输出也就跟着改变，如：1. //第⼀个线程2. UINT FirstThread(LPVOIDlParam)3. {4.

5. for(int i =0; i<10;i++){6. EnterCriticalSection(&cs);///进⼊临界区，临界区移到for循环内部⾥7. n_AddValue ++;8. cout <<"n_AddValue in FirstThread is"<

9. LeaveCriticalSection(&cs);//离开临界区10. }

11. return 0;12. }13.

14. //第⼆个线程15. UINT SecondThread(LPVOIDlParam)16. {17.

18. for(int i =0; i<10;i++){

19. EnterCriticalSection(&cs);//进⼊临界区20. n_AddValue ++;

21. cout <<"n_AddValue in SecondThread is"<

也正由于CRITICAL_SECTION是这样发挥作⽤的，所以，必须把每⼀个线程中访问共享资源的语句都放在EnterCritialSection和LeaveCriticalSection之间。这是初学者很容易忽略的地⽅。当然，上⾯说的都是对于同⼀个CRITICAL_SECTION⽽⾔的。 如果⽤到两个CRITICAL_SECTION，⽐如说：

第⼀个线程已经执⾏了EnterCriticalSection(&cs)并且还没有执⾏LeaveCriticalSection(&cs)，这时另⼀个线程想要执⾏EnterCriticalSection(&cs2)，这种情况是可以的（除⾮cs2已经被第三个线程抢先占⽤了）。 这也就是多个CRITICAL_SECTION实现同步的思想。