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:

C++ 事件(event)使用总结


上一篇:Nginx 教程- 获取真实IP模块 - http_realip_module


下一篇:kafka实现无消息丢失与精确一次语义(exactly once)处理