C++ 事件（event）使用总结

  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：