二. WaitForMultipleObject 等待单个线程返回
1. 函数原型
DWORD WINAPI WaitForMultipleObjects( _In_ DWORD nCount, _In_ const HANDLE *lpHandles, _In_ BOOL bWaitAll, _In_ DWORD dwMilliseconds );2. 参数说明
第一个参数 nCount 为等待的内核对象个数，可以是 0 到 MAXIMUM_WAIT_OBJECTS （64）中的一个值。第二个参数 lpHandles 为一个存放被等待的内核对象句柄的数组。第三个参数 bWaitAll 是否等到所有内核对象为已通知状态后才返回，如果为 TRUE，则只有当等待的所有内核对象为已通知状态时函数才返回，如果为 FALSE，则只要一个内核对象为已通知状态，则该函数返回。第四个参数 dwMilliseconds 为等待时间，和 WaitForSingleObject 中等待 dwMilliseconds 参数类似。3. 返回值
WAIT_ABANDONED_0 表示所有对象都发出消息，而且其中有一个或对个属于互斥体（一旦拥有他们的进程结束，就会发出信号）WAIT_TIMEOUT 对象保持未发出信号的状态，但规定的等待超时时间已经超过WAIT_OBJECT_0 所有对象都发出信号WAIT_FAILED 表示函数执行失败，会设置错误码，错误码可通过 GetLastError 获取WAIT_IO_COMPLETION （仅适用于 WaitForMultipleObjectsEx ）由于一个 I/O 完成操作已做好准备执行，所以造成了函数的返回值 —— 如果 bWaitAll 为 FALSE，那么返回结果相似，只是可能还会返回相对于 WAIT_ABANDONED_0 或 WAIT_OBJECT_0 的一个正偏移量，指出哪个对象时被抛弃还是发出信号。补充: WAIT_OBJECT_0 时微软定义的一个宏，就可以把这个宏当做一个数字。例如， 返回值 WAIT_OBJECT_0 + 5 意味着列表中的第 5 个对象发出了信号。当 bWaitAll 参数为 FALSE 时可以等待其中之一的信号。
4. 示例
（1）参数 bWaitAll 为 FALSE，只要一个内核对象为已通知状态，则该函数返回。
#include <Windows.h> #include <stdio.h> const unsigned int THREAD_NUM = 3; DWORD WINAPI ThreadFunc(LPVOID p) { printf("I am a child thread 0 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(500); printf("The child thread 0 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } DWORD WINAPI ThreadFunc1(LPVOID p) { printf("I am a child thread 1 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(2000); printf("The child thread 1 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } DWORD WINAPI ThreadFunc2(LPVOID p) { printf("I am a child thread 2 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(4000); printf("The child thread 2 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } int main() { printf("I am the main thread that pid is %d ...\n", GetCurrentThreadId()); //输出主线程pid HANDLE hThread[THREAD_NUM]; hThread[0] = CreateThread(NULL, 0, ThreadFunc, 0, 0, NULL); // 创建线程 hThread[1] = CreateThread(NULL, 0, ThreadFunc1, 0, 0, NULL); // 创建线程 hThread[2] = CreateThread(NULL, 0, ThreadFunc2, 0, 0, NULL); // 创建线程 DWORD resulut = WaitForMultipleObjects(THREAD_NUM, hThread, FALSE, INFINITE); //只要有一个线程返回就结束 if (WAIT_OBJECT_0 == resulut) { printf("The child thread 0 finished waiting ...\n"); } else if (WAIT_OBJECT_0 + 1 == resulut) { printf("The child thread 1 finished waiting ...\n"); } else if (WAIT_OBJECT_0 + 2 == resulut) { printf("The child thread 2 finished waiting ...\n"); } else if (WAIT_FAILED == resulut) { printf("The fuction WaitForMultipleObjects error! \n"); } printf("The main thread which pid is %d quit ...\n", GetCurrentThreadId()); return 0; }输出结果为：
—— 如果将代码中的 “Thread 0” 的 Sleep 时间加长，让 “Thread 1” 先退出，则 会进入 WAIT_OBJECT_0 + 1 == resulut 分支，打印 “The child thread 1 finished waiting ...”，然后退出主线程。这样就可以通过返回值判断是哪个对象发送的信号。
（2）参数 bWaitAll 为 TRUE，等待所有线程返回。
#include <Windows.h> #include <stdio.h> const unsigned int THREAD_NUM = 3; DWORD WINAPI ThreadFunc(LPVOID p) { printf("I am a child thread 0 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(500); printf("The child thread 0 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } DWORD WINAPI ThreadFunc1(LPVOID p) { printf("I am a child thread 1 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(2000); printf("The child thread 1 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } DWORD WINAPI ThreadFunc2(LPVOID p) { printf("I am a child thread 2 which pid is %d ...\n", GetCurrentThreadId()); //输出子线程pid Sleep(4000); printf("The child thread 2 which pid is %d quit ...\n", GetCurrentThreadId()); return 0; } int main() { printf("I am the main thread that pid is %d ...\n", GetCurrentThreadId()); //输出主线程pid HANDLE hThread[THREAD_NUM]; //创建第一个子线程 hThread[0] = CreateThread(NULL, 0, ThreadFunc, 0, 0, NULL); // 创建线程 hThread[1] = CreateThread(NULL, 0, ThreadFunc1, 0, 0, NULL); // 创建线程 hThread[2] = CreateThread(NULL, 0, ThreadFunc2, 0, 0, NULL); // 创建线程 int wait_num = 0; while (wait_num < THREAD_NUM) { DWORD resulut = WaitForMultipleObjects(THREAD_NUM, hThread, TRUE, INFINITE); //所有子线程返回才结束 if (WAIT_OBJECT_0 <= resulut <= WAIT_OBJECT_0 + 2) { printf("The Return value is %d, One child thread finished waiting ...\n", resulut); wait_num++; } } printf("The main thread which pid is %d quit ...\n", GetCurrentThreadId()); return 0; }输出结果为：
转载于:https://www.cnblogs.com/rock-cc/p/9371898.html
