再谈线程等待函数WaitForSingleObject和CloseHandle

多线程中使用WaitForSingleObject结束线程，啥也不说，先上代码

#include 
#include 
#include 

int Fun1Proc( void )
{
	int i;
	char *c = "thread one " ; 
	for(i = 0; i < 100; i++)
	{
		printf("%s number: %d \n",c ,i+1 );
	}	
	return 0;
}


int main(  )
{
	HANDLE hThread1;
	hThread1 = CreateThread(NULL, 0, Fun1Proc, NULL, 0, NULL);
	int i;
	char *c = "main thread " ; 
	for(i = 0; i < 100; i++)
	{
		printf("%s number: %d \n",c ,i+1 );
	}
	CloseHandle(hThread1);

	return 0;
}

执行结果：

main thread 1
main thread 2
main thread 3
...

main thread 98
main thread 99
main thread 100

为什么线程函数没有执行呢？奇怪，多运行几遍，发现每次结果不一定相同，下面是另一次执行结果：

main thread 1
main thread 2
main thread 3

...

main thread 71

thread one 1
thread one 2

main thread 72

main thread 73

...

thread one 3
thread one 4

main thread 75

main thread 76

...

main thread 98
main thread 99
main thread 100

可见，主函数运行完了，整个程序就退出了，不会等到Fun1Proc（）运行完再退出。等2秒会不会好一点呢？下面是修改后的main程序

int main(  )
{
	HANDLE hThread1;
	hThread1 = CreateThread(NULL, 0, Fun1Proc, NULL, 0, NULL);
	Sleep(2000);

	int i;
	char *c = "main thread " ; 
	for(i = 0; i < 100; i++)
	{
		printf("%s number: %d \n",c ,i+1 );
	}
	

	return 0;
}

运行结果：
thread one 1
thread one 2
thread one 3

...

thread one 98
thread one 99
thread one 100

main thread 1
main thread 2
main thread 3
...

main thread 98
main thread 99
main thread 100

这下貌似可以，但这个2秒只是估算的一个时间，并不准确，有的线程执行时间很长的，代码还要再修改下：

int main(  )
{
	HANDLE hThread1;
	hThread1 = CreateThread(NULL, 0, Fun1Proc, NULL, 0, NULL);
	WaitForSingleObject(hThread1, INFINITE);

	int i;
	char *c = "main thread " ; 
	for(i = 0; i < 100; i++)
	{
		printf("%s number: %d \n",c ,i+1 );
	}
	CloseHandle(hThread1);

	return 0;
}

这下好了，每次运行结果都正确，WaitForSingleObject的作用就是等待线程自动结束，继续执行后面的程序。这个CloseHandle为什么这么靠后呢？把它放前面一点好不好？不是说每次创建线程以后直接 CloseHandle更好吗？好，那就挪到上面试试

int main(  )
{
	HANDLE hThread1;
	hThread1 = CreateThread(NULL, 0, Fun1Proc, NULL, 0, NULL);
	CloseHandle(hThread1);
	WaitForSingleObject(hThread1, INFINITE);

	int i;
	char *c = "main thread " ; 
	for(i = 0; i < 100; i++)
	{
		printf("%s number: %d \n",c ,i+1 );
	}
	

	return 0;
}

运行后发现，又和一开始一样了，main thread 中穿插着 thread one。 原来是CloseHandle之后，WaitForSingleObject得不到thread的句柄，没法再等到这个thread结束，呵呵。所以，如果后面还要用到这个thread句柄，就不要closeHandle；如果用不到，就可以先closeHandle。