c++CreateEvent函数在多线程中使用及实例
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CreateEvent函数详解参见本博客文章:
c++中CreateEvent函数解析(2)
HANDLE CreateEvent(
LPSECURITY_ATTRIBUTES lpEventAttributes,
BOOL bManualReset,
BOOL bInitialState,
LPCSTR lpName
);
bManualReset:TRUE,使用ResetEvent()手动重置为无信号状态;FALSE,当一个等待线程被释放时,自动重置状态为无信号状态。
bInitialState:指定事件对象的初始状态,当TRUE,初始状态为有信号状态;当FALSE,初始状态为无信号状态。
下面主要演示一下采用CreateEvent实现多线程。
例子很简单,主要测试CreateEvent中bManualReset:和bInitialState参数的取值在线程调用中信号状态的情况。
测试1:
bManualReset:TRUE
bInitialState:TRUE
CreateEvent(NULL, TRUE, TRUE, NULL); //使用手动重置为无信号状态,初始化时有信号状态
example.cpp
#include "iostream"#include "windows.h"using namespace std;DWORD WINAPI ThreadProc1(LPVOID lpParam);DWORD WINAPI ThreadProc2(LPVOID lpParam);HANDLE hEvent = NULL;HANDLE hThread1 = NULL;HANDLE hThread2 = NULL;int main(int argc, char *args[]){hEvent = CreateEvent(NULL, TRUE, TRUE, NULL); //使用手动重置为无信号状态,初始化时有信号状态//hEvent = CreateEvent(NULL, FALSE, TRUE, NULL); //当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态//if (SetEvent(hEvent))//{//cout << "setEvent 成功" <<endl;//}hThread1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc1, NULL, 0,NULL);Sleep(200);hThread2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc2, NULL, 0,NULL);Sleep(200);if ( NULL == hThread1){cout <<"create thread fail!";}//DWORD dCount = ResumeThread(hThread);//cout << LOWORD(dCount) << endl;return 0;}DWORD WINAPI ThreadProc1(LPVOID lpParam){cout <<"in thread1@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<" thread1 signaled ! "<<endl;}cout <<"in thread1 --signal"<<endl;//SetEvent(hEvent);return 0;}DWORD WINAPI ThreadProc2(LPVOID lpParam){cout <<"in thread2@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<"thread2 signaled ! "<<endl;}cout <<"in thread2--signal"<<endl;return 0;}
执行结果:
从结果中看,执行完线程1又执行了线程2.
由于hEvent = CreateEvent(NULL, TRUE, TRUE, NULL),使用手动重置为无信号状态,初始化时有信号状态
所以hEvent一直处于有信号状态,无论是线程1释放后,hEvent仍处于有信号状态,所以线程2正常执行了。
测试2:
bManualReset:FALSE
bInitialState:TRUE
hEvent = CreateEvent(NULL, FALSE, TRUE, NULL); //当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态
example2.cpp
#include "iostream"#include "windows.h"using namespace std;DWORD WINAPI ThreadProc1(LPVOID lpParam);DWORD WINAPI ThreadProc2(LPVOID lpParam);HANDLE hEvent = NULL;HANDLE hThread1 = NULL;HANDLE hThread2 = NULL;int main(int argc, char *args[]){//hEvent = CreateEvent(NULL, TRUE, TRUE, NULL); //使用手动重置为无信号状态,初始化时有信号状态hEvent = CreateEvent(NULL, FALSE, TRUE, NULL); //当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态//if (SetEvent(hEvent))//{//cout << "setEvent 成功" <<endl;//}hThread1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc1, NULL, 0,NULL);Sleep(200);hThread2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc2, NULL, 0,NULL);Sleep(200);if ( NULL == hThread1){cout <<"create thread fail!";}//DWORD dCount = ResumeThread(hThread);//cout << LOWORD(dCount) << endl;return 0;}DWORD WINAPI ThreadProc1(LPVOID lpParam){cout <<"in thread1@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<" thread1 signaled ! "<<endl;}cout <<"in thread1 --signal"<<endl;//SetEvent(hEvent);return 0;}DWORD WINAPI ThreadProc2(LPVOID lpParam){cout <<"in thread2@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<"thread2 signaled ! "<<endl;}cout <<"in thread2--signal"<<endl;return 0;}
执行结果:
从执行结果中分析,执行了线程1,线程2一直在等待,直到主线程结束。
由于hEvent = CreateEvent(NULL, FALSE, TRUE, NULL),当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态
初始执行线程1的时候,hEvent是有信号的,所以线程1正常执行;又由于bManualReset=FALSE,所以执行完线程1后,hEvent自动重置为无信号状态,所以在线程2中,
WaitForSingleObject(hEvent,INFINITE);函数一直在等待hEvent变为有信号状态,但是当主线程执行完,还没等待到,线程2程序一直没有走下去。
测试3:
bManualReset:TRUE
bInitialState:FALSE
hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);//使用手动重置为无信号状态,初始化时为无信号状态
example3.cpp
#include "iostream"#include "windows.h"using namespace std;DWORD WINAPI ThreadProc1(LPVOID lpParam);DWORD WINAPI ThreadProc2(LPVOID lpParam);HANDLE hEvent = NULL;HANDLE hThread1 = NULL;HANDLE hThread2 = NULL;int main(int argc, char *args[]){//hEvent = CreateEvent(NULL, TRUE, TRUE, NULL); //使用手动重置为无信号状态,初始化时有信号状态//hEvent = CreateEvent(NULL, FALSE, TRUE, NULL); //当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);//使用手动重置为无信号状态,初始化时为无信号状态//if (SetEvent(hEvent))//{//cout << "setEvent 成功" <<endl;//}hThread1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc1, NULL, 0,NULL);Sleep(200);hThread2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc2, NULL, 0,NULL);Sleep(200);if ( NULL == hThread1){cout <<"create thread fail!";}//DWORD dCount = ResumeThread(hThread);//cout << LOWORD(dCount) << endl;return 0;}DWORD WINAPI ThreadProc1(LPVOID lpParam){cout <<"in thread1@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<" thread1 signaled ! "<<endl;}cout <<"in thread1 --signal"<<endl;//SetEvent(hEvent);return 0;}DWORD WINAPI ThreadProc2(LPVOID lpParam){cout <<"in thread2@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<"thread2 signaled ! "<<endl;}cout <<"in thread2--signal"<<endl;return 0;}
执行结果,可想而知,只能输出:
in thread1@!
in thread2@!因为初始为无信号状态,所以hEvent一直处于无信号状态,因此这两个线程一直在等待,直到主线程结束。
修改:放开例子中的注释部分:
if (SetEvent(hEvent))//设置信号为有信号状态
{
cout << "setEvent 成功" <<endl;
}
执行结果:
可见,线程1和线程2都执行了。
因为调用SetEvent,事件变为有信号状态,线程1执行;又由于线程1释放后,hEvent仍旧处于有信号状态,所以线程2也执行了。
再修改:在线程1中,添加ResetEvent(hEvent)(手动设置事件为无信号状态),则线程2不会执行。
测试4:
bManualReset:FALSE
bInitialState:FALSE
hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);//线程释放后自动重置为无信号状态,初始化时为无信号状态
example4.cpp
#include "iostream"#include "windows.h"using namespace std;DWORD WINAPI ThreadProc1(LPVOID lpParam);DWORD WINAPI ThreadProc2(LPVOID lpParam);HANDLE hEvent = NULL;HANDLE hThread1 = NULL;HANDLE hThread2 = NULL;int main(int argc, char *args[]){//hEvent = CreateEvent(NULL, TRUE, TRUE, NULL); //使用手动重置为无信号状态,初始化时有信号状态//hEvent = CreateEvent(NULL, FALSE, TRUE, NULL); //当一个等待线程被释放时,自动重置为无信号状态,初始是有信号状态//hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);//使用手动重置为无信号状态,初始化时为无信号状态hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);//使用手动重置为无信号状态,初始化时为无信号状态if (SetEvent(hEvent)){cout << "setEvent 成功" <<endl;}hThread1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc1, NULL, 0,NULL);Sleep(200);hThread2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc2, NULL, 0,NULL);Sleep(200);if ( NULL == hThread1){cout <<"create thread fail!";}//DWORD dCount = ResumeThread(hThread);//cout << LOWORD(dCount) << endl;return 0;}DWORD WINAPI ThreadProc1(LPVOID lpParam){cout <<"in thread1@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<" thread1 signaled ! "<<endl;}cout <<"in thread1 --signal"<<endl;//SetEvent(hEvent);return 0;}DWORD WINAPI ThreadProc2(LPVOID lpParam){cout <<"in thread2@!"<<endl;DWORD dReturn = WaitForSingleObject(hEvent,INFINITE);if ( WAIT_OBJECT_0 == dReturn){cout <<"thread2 signaled ! "<<endl;}cout <<"in thread2--signal"<<endl;return 0;}
执行结果:
由于调用SetEvent,hEvent为有信号状态,线程1正常执行,又由于调用完线程1后,hEvent自动重置为无信号状态,所以线程2只能在等待,直到主线程退出。
修改:线程1中的SetEvent(hEvent);的注释去掉,再运行,则线程1和线程2 都会执行。
- c++CreateEvent函数在多线程中使用及实例
- c++CreateEvent函数在多线程中使用及实例
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