windows,三个线程（+ ，- ，*）;WaiForSingleObject；-优快云博客

本文展示了一个使用C语言编写的多线程程序示例，该程序创建了三个线程来分别对全局变量进行加、减和乘操作，并通过循环展示了线程间的并发执行过程。由于未使用线程同步机制如临界区，因此示例中存在竞态条件导致的输出不确定性。

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int g_num = 0;
//CRITICAL_SECTION g_cs;
unsigned __stdcall FirstThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num += 5;
printf("FirstThread g_num is %d\n", g_num);
//LeaveCriticalSection(&g_cs);
_endthread();
return 0;
}

unsigned __stdcall SecondThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num -= 2;
printf("SecondThread g_num is %d \n", g_num);
//LeaveCriticalSection(&g_cs);
_endthread();
return 0;
}

unsigned __stdcall ThirdThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num *= 2;
printf("ThirdThread g_num is %d \n", g_num);
//LeaveCriticalSection(&g_cs);
_endthread();
return 0;
}
void main()
{
unsigned threadID1;
unsigned threadID2;
unsigned threadID3;
int i = 20;
while (i -- >0)
{
HANDLE hd1 = (HANDLE)_beginthreadex(NULL, 0, &FirstThread, NULL, 0, &threadID1);
WaitForSingleObject(hd1, INFINITE);
CloseHandle(hd1);
HANDLE hd2 = (HANDLE)_beginthreadex(NULL, 0, &SecondThread, NULL, 0, &threadID2);
WaitForSingleObject(hd2, INFINITE);
CloseHandle(hd2);
HANDLE hd3 = (HANDLE)_beginthreadex(NULL, 0, &ThirdThread, NULL, 0, &threadID3);
WaitForSingleObject(hd3, INFINITE);
CloseHandle(hd3);
}

system("pause");

}

/////////////最好是下面的////////////

int g_num = 0;
//CRITICAL_SECTION g_cs;
unsigned __stdcall FirstThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num += 5;
printf("FirstThread g_num is %d\n", g_num);
//LeaveCriticalSection(&g_cs);
_endthreadex(0);
return 0;
}

unsigned __stdcall SecondThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num -= 2;
printf("SecondThread g_num is %d \n", g_num);
//LeaveCriticalSection(&g_cs);
_endthreadex(0);
return 0;
}

unsigned __stdcall ThirdThread(void *p)
{
//EnterCriticalSection(&g_cs);
g_num *= 2;
printf("ThirdThread g_num is %d \n", g_num);
//LeaveCriticalSection(&g_cs);
_endthreadex(0);
return 0;
}
void main()
{
unsigned threadID1;
unsigned threadID2;
unsigned threadID3;
int i = 20;
while (i -- >0)
{
HANDLE hd1 = (HANDLE)_beginthreadex(NULL, 0, &FirstThread, NULL, 0, &threadID1);
WaitForSingleObject(hd1, INFINITE);
CloseHandle(hd1);
HANDLE hd2 = (HANDLE)_beginthreadex(NULL, 0, &SecondThread, NULL, 0, &threadID2);
WaitForSingleObject(hd2, INFINITE);
CloseHandle(hd2);
HANDLE hd3 = (HANDLE)_beginthreadex(NULL, 0, &ThirdThread, NULL, 0, &threadID3);
WaitForSingleObject(hd3, INFINITE);
CloseHandle(hd3);
}

system("pause");
}