C++ 事件（event）使用总结

痛定思痛。 2022-12-03 11:28 515阅读 0赞

事件最常用在多线程同步互斥机制。

常用的函数有：

1、CreateEvent 创建事件。

函数原型如下所示，一共四个参数：

HANDLE CreateEvent(

LPSECURITY\_ATTRIBUTES lpEventAttributes,　// SECURITY\_ATTRIBUTES结构指针，可为NULL  
　BOOL bManualReset,     // 手动/自动  
　                                    // TRUE：表示手动，在WaitForSingleObject后必须手动调用ResetEvent清除信号  
　                                   // FALSE：表示自动，在WaitForSingleObject后，系统自动清除事件信号  
　BOOL bInitialState,        //初始状态，FALSE为无信号，TRUE为有信号  
　LPCTSTR lpName         //事件的名称  
    );

2、SetEvent：设置为激活触发状态。

3、ResetEvent：设置为未激活触发状态。

4、WaitForSingleObject：检测信号，如果未激活，代码就会处于挂起状态，不再往下执行。

下面是多线程同步的示例：

#include <tchar.h> 
    #include <iostream>
    #include <wtypes.h>
    using namespace std;
    
    DWORD WINAPI ThreadProc(LPVOID lpParam);
    DWORD WINAPI ThreadProc2(LPVOID lpParam);
    DWORD g_dwThreadID;
    DWORD g_dwThreadID2;
    UINT g_nTickets = 300;  
    HANDLE g_hEvent1 = NULL;
    HANDLE g_hEvent2 = NULL;
    CRITICAL_SECTION g_cs;
    int ThreadCout = 0;
    
    int main(int argc, _TCHAR* argv[])
    {
    	cout << "Main thread is running." << endl;
    	InitializeCriticalSection(&g_cs);//初始化临界区
    	HANDLE hHandle = CreateThread(NULL, 0, ThreadProc, NULL, 0, &g_dwThreadID);
    	ThreadCout++;
    	HANDLE hHandle2 = CreateThread(NULL, 0, ThreadProc2, NULL, 0, &g_dwThreadID2);
    	ThreadCout++;
    	g_hEvent1 = CreateEvent(NULL, FALSE, TRUE, NULL);  //备注5:g_hEvent1 = CreateEvent(NULL, TRUE,  TRUE, NULL);
    	g_hEvent2 = CreateEvent(NULL, FALSE, TRUE, NULL);  //备注5:g_hEvent2 = CreateEvent(NULL, TRUE,  TRUE, NULL);
    	ResetEvent(g_hEvent1);
    	ResetEvent(g_hEvent2);
    	SetEvent(g_hEvent1);
    	while (TRUE)
    	{
    		EnterCriticalSection(&g_cs);
    		int nCount = ThreadCout;
    		LeaveCriticalSection(&g_cs);
    		if (nCount == 0)
    		{
    			cout << "Main break" << endl;
    			break;
    		}
    	}
    	Sleep(1000);    //备注4
    	CloseHandle(hHandle);
    	CloseHandle(hHandle2);
    	DeleteCriticalSection(&g_cs);
    	cout << "Main End " << endl;
    	system("pause");
    	return 0;
    }
    
    DWORD WINAPI ThreadProc(LPVOID lpParam)
    {
    	while (TRUE)
    	{
    		WaitForSingleObject(g_hEvent1, INFINITE);
    		cout << "线程1：" << g_dwThreadID << " thread is running." << endl;
    		EnterCriticalSection(&g_cs);
    		int temp = g_nTickets;
    		LeaveCriticalSection(&g_cs);
    		cout << "线程1：" << g_dwThreadID << " thread is temp." << endl;
    		if (temp > 0)
    		{
    			Sleep(100);  //Sleep(1000)   
    			cout << "线程1：" << g_dwThreadID << " sell ticket : " << temp << endl;
    			EnterCriticalSection(&g_cs);
    			g_nTickets--;
    			LeaveCriticalSection(&g_cs);
    			SetEvent(g_hEvent2);
    		}
    		else
    		{
    			cout << "线程1 break" << endl;
    			SetEvent(g_hEvent2);//没有这个ThreadProc2不能终止   
    			break;
    		}
    	}
    	EnterCriticalSection(&g_cs);
    	ThreadCout--;
    	LeaveCriticalSection(&g_cs);
    	cout << "线程1 end" << endl;
    	return 0;
    }
    
    DWORD WINAPI ThreadProc2(LPVOID lpParam)
    {
    	while (TRUE)
    	{
    		WaitForSingleObject(g_hEvent2, INFINITE);
    		cout << "线程2： " << g_dwThreadID2 << " thread is running." << endl;
    		EnterCriticalSection(&g_cs);
    		int temp = g_nTickets;
    		LeaveCriticalSection(&g_cs);
    		if (temp > 0)
    		{
    			Sleep(100);  //Sleep(1000)   //备注2
    			cout << "线程2：" << g_dwThreadID2 << " sell ticket : " << temp << endl;
    			EnterCriticalSection(&g_cs);
    			g_nTickets--;
    			LeaveCriticalSection(&g_cs);
    			SetEvent(g_hEvent1);			
    		}
    		else
    		{
    			cout << "线程2 break" << endl;			
    			SetEvent(g_hEvent1);//同样的问题，没有这个ThreadProc不能终止
    			break;
    		}
    	}
    	EnterCriticalSection(&g_cs);
    	ThreadCout--;
    	LeaveCriticalSection(&g_cs);
    	cout << "线程2 end" << endl;
    	return 0;
    }

执行结果如下图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hoaGhoaGhoaGh3d3d3d3d3d3d3_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hoaGhoaGhoaGh3d3d3d3d3d3d3_size_16_color_FFFFFF_t_70]: /images/20221123/8de4419a71c74c50bdd8dc6546cb84ff.png