1.CreateThread与_beginthreadex
#pragma once #include<cstdio> #include<Windows.h> #include<crtdbg.h> #include<process.h> //子线程函数 DWORD WINAPI ThreadFun1(LPVOID pM) { printf("子线程的线程ID号为：%d Hello world! ",GetCurrentThreadId()); return 0; } void fun1() { printf("简单多线程实例！ "); /* CreateThread参数解析 1:线程内核安全属性 2：线程栈空间大小 3：线程执行函数地址 4：传给线程执行函数参数 5：线程创建控制参数(CREATE_SUSPENDED) 6：线程ID号 */ HANDLE handle = CreateThread(NULL, 0, ThreadFun1, NULL, 0, NULL); WaitForSingleObject(handle, INFINITE); CloseHandle(handle); } //设置计数全局变量 int COUNT = 0; //子线程函数 unsigned int _stdcall ThreadFun2(PVOID pM) { ++COUNT; printf("子线程的线程ID号为：%d，报数为%d Hello world! ", GetCurrentThreadId(),COUNT); return 0; } void fun2() { printf("简单多线程实例！ "); const int THREAD_NUM = 5; HANDLE handle[THREAD_NUM]; for (size_t i = 0; i < THREAD_NUM; i++) { handle[i] = (HANDLE)_beginthreadex(NULL, 0, ThreadFun2, NULL, 0, NULL); } WaitForMultipleObjects(THREAD_NUM, handle, TRUE, INFINITE); } int main(void) { //使用CreateThread //fun1(); //使用_beginthreadex //推荐使用原因为：使用标准C运行库函数时，易发生race condition //使用_beginthreadex可以避免数据被其他线程篡改 //更加合理的解释可以参考Win32多线程编程 fun2(); //检测内存泄漏 _CrtDumpMemoryLeaks(); return 0; }
其中执行fun2结果为：（蛮有趣的，不加锁竟然这么直观）
2.原子操作
#pragma once #include<cstdio> #include<Windows.h> #include<crtdbg.h> #include<process.h> volatile long COUNT = 0; const int THREAD_NUM = 500; unsigned int _stdcall ThreadFun1(LPVOID pM) { Sleep(50); //++COUNT; InterlockedIncrement((LPLONG)&COUNT); //使用原子锁替换 Sleep(50); return 0; } unsigned int _stdcall ThreadFun2(LPVOID pM) { Sleep(50); InterlockedIncrement((LPLONG)&COUNT); //使用原子锁替换 printf("线程编号为%d,全局资源值为%d ", *(int *)pM, COUNT); return 0; } void fun1() { HANDLE handle[THREAD_NUM]; for (size_t i = 0; i < THREAD_NUM; i++) { handle[i] = (HANDLE)_beginthreadex(NULL, 0, ThreadFun1, NULL, 0, NULL); } WaitForMultipleObjects(THREAD_NUM, handle, TRUE, INFINITE); printf("有%d个线程启动,记录结果为%d", THREAD_NUM, COUNT); } void fun2() { HANDLE handle[THREAD_NUM]; for (size_t i = 0; i < THREAD_NUM; i++) { handle[i] = (HANDLE)_beginthreadex(NULL, 0, ThreadFun2, &i, 0, NULL); } WaitForMultipleObjects(THREAD_NUM, handle, TRUE, INFINITE); } int main() { //test1 //fun1(); //易发现线程启动数和计数不匹配 //test2 fun2(); //线程编号和全局资源值 //检测内存泄漏 _CrtDumpMemoryLeaks(); return 0; }
fun1：这里++操作在汇编层面是分成三层的：（1）取值由内存存至寄存器；（2）寄存器中进行操作；（3）数值由寄存器转储至内存。这个过程容易出现问题。
但是使用原子操作在只有50个线程启动时准确，但是上限调至500次时，线程启动数和计数又不一致（个人理解我inc虽然汇编下为一个操作，但是实际会分为多层次执行）。
fun2:运行结果更为混乱，其中原子操作部分不表。
线程ID不准确的原因是i在传递至子线程函数的过程中，在主线程中就已经被修改数值了。
3.关键区域同步（CRITICAL_SECTION）
#pragma once #include<cstdio> #include<Windows.h> #include<crtdbg.h> #include<process.h> unsigned int count = 0; const int threadnum = 50; CRITICAL_SECTION ThreadPar1, ThreadPar2; unsigned int _stdcall ThreadFun(LPVOID pM) { UINT num = *(UINT*)pM; //离开子线程ID号关键区域 LeaveCriticalSection(&ThreadPar1); Sleep(50); //做点什么 EnterCriticalSection(&ThreadPar2); ++count; printf("线程编号为%3d,全局资源值为%3d ", num, count); LeaveCriticalSection(&ThreadPar2); return 0; } int main() { InitializeCriticalSection(&ThreadPar1); InitializeCriticalSection(&ThreadPar2); HANDLE handle[threadnum]; for (UINT i = 0; i < threadnum; i++) { //进入子线程ID号关键区域 EnterCriticalSection(&ThreadPar1); handle[i] = (HANDLE)_beginthreadex(NULL, 0, ThreadFun, &i, 0, NULL); } WaitForMultipleObjects(threadnum, handle, TRUE, INFINITE); DeleteCriticalSection(&ThreadPar1); DeleteCriticalSection(&ThreadPar2); //检测内存泄漏 _CrtDumpMemoryLeaks(); return 0; }
输出结果：（嘿嘿，ID号不正确，计数正确）
出现此问题的原因在于ThreadPar1的线程所有权是主线程，而不是子线程，这也就导致其可以多次进入关键区域，继而导致ID号不同。
而ThreadPar2的线程所有权是子线程，所以不出出现这个问题，输出正常。
这也从侧面证明CRITICAL_SECTION无法解决同步问题，而只能解决互斥问题。
4.事件（Event）
#pragma once #define _CRTDBG_MAP_ALLOC #include<cstdio> #include<Windows.h> #include<crtdbg.h> #include<process.h> unsigned int count = 0; const int threadnum = 50; HANDLE ThreadEvent; CRITICAL_SECTION ThreadPar; unsigned int _stdcall ThreadFun1(LPVOID pM) { int num = *(int*)pM; SetEvent(ThreadEvent); //触发事件 Sleep(50); //some work should to do EnterCriticalSection(&ThreadPar); ++count; printf("线程编号为%d,全局资源值为%d ", num, count); LeaveCriticalSection(&ThreadPar); return 0; } void fun1() { //初始化事件（自动置位，初始无触发的匿名事件）和关键段 /*CreateEvent参数说明 1：安全控制 2：手动置位（true）/自动置位（false） 自动置位，对事件调用WaitForSingleObject后， 会自动调用ResetEvent使事件变为未触发状态 3：事件初始状态（TRUE表示已触发） 4：事件名称（NULL表示匿名） */ ThreadEvent = CreateEvent(NULL, false, false, NULL); InitializeCriticalSection(&ThreadPar); size_t i; HANDLE handle[threadnum]; for (i = 0; i < threadnum; i++) { handle[i] = (HANDLE)_beginthreadex(NULL, 0, ThreadFun1, &i, 0, NULL); WaitForSingleObject(ThreadEvent, INFINITE); } WaitForMultipleObjects(threadnum, handle, TRUE, INFINITE); //销毁时间和关键段 CloseHandle(ThreadEvent); DeleteCriticalSection(&ThreadPar); for ( i = 0; i < threadnum; i++) { CloseHandle(handle[i]); } } unsigned int _stdcall FastThreadFun(LPVOID pM) { Sleep(10); //以此来保证各线程调用等待函数的次序具有随机性 printf("%s 启动 ", (PSTR)pM); WaitForSingleObject(ThreadEvent, INFINITE); printf("%s 等到事件被触发，顺利结束 ", (PSTR)pM); return 0; } unsigned int _stdcall SlowThreadFun(LPVOID pM) { Sleep(100); //以此来保证各线程调用等待函数的次序具有随机性 printf("%s 启动 ", (PSTR)pM); WaitForSingleObject(ThreadEvent, INFINITE); printf("%s 等到事件被触发，顺利结束 ", (PSTR)pM); return 0; } void fun2() { bool bManualReset = true; ThreadEvent = CreateEvent(NULL, bManualReset, false, NULL); if (bManualReset) { printf("当前使用手动置位事件 "); } else { printf("当前使用自动置位事件 "); } char szFast[5][30]{ "快线程001","快线程002","快线程003","快线程004","快线程005" }; char szSlow[5][30]{ "慢线程001","慢线程002","慢线程003","慢线程004","慢线程005" }; size_t i = 0; for ( i = 0; i < 5; i++) { _beginthreadex(NULL, 0, FastThreadFun, szFast[i], 0, NULL); } for (i = 0; i < 5; i++) { _beginthreadex(NULL, 0, SlowThreadFun, szSlow[i], 0, NULL); } Sleep(50); //确保快线程已经全部启动 printf("现在主线程触发事件脉冲-PlusEvent "); PulseEvent(ThreadEvent); //调用PulseEvent()就相当于同时调用下面二句 //SetEvent(ThreadEvent); //ResetEvent(ThreadEvent); Sleep(3000); printf("时间到,主线程结束运行 "); CloseHandle(ThreadEvent); } int main(void) { //test1 //fun1(); //test2 fun2(); //检测内存泄漏 _CrtDumpMemoryLeaks(); return 0; }
fun1：成功解决临界资源的问题
fun2：PulseEvent：
函数说明：这是一个不常用的事件函数，此函数相当于SetEvent()后立即调用ResetEvent();此时情况可以分为两种：
1.对于手动置位事件，所有正处于等待状态下线程都变成可调度状态。
2.对于自动置位事件，所有正处于等待状态下线程只有一个变成可调度状态（随机）。
