多线程文件操作时一定要注意的地方

首先看一下源代码

#include 
#include 

void test()
{
	FILE *fp = fopen("d:\\aaa.txt",  "a+");
	fprintf(fp, "hello\n"); 
	fclose(fp);
}	

DWORD WINAPI ThreadFun(LPVOID pM)
{
	test();

	return 0;
}

int main()
{  
	printf("main thread\n");

	int i = 0;

	for(i = 0; i < 10; i++)
	{
		HANDLE handle = CreateThread(NULL, 0, ThreadFun, NULL, 0, NULL);
		CloseHandle(handle);	
	}

	getchar();
	
	printf("end\n");

	return 0;
}

执行时发现，不是每次都打印10个hello，有时打印9个，有时13个？？？

下面， 我们对用互斥对象对多线程下的文件操作进行保护（互斥锁）， 简要的示意代码如下：

#include 
#include 

HANDLE hMutex = NULL;  

void test()
{
	WaitForSingleObject(hMutex, INFINITE);  

	FILE *fp = fopen("d:\\aaa.txt",  "a+");
	fprintf(fp, "hello\n"); 
	fclose(fp);

	ReleaseMutex(hMutex);  
}	



DWORD WINAPI ThreadFun(LPVOID pM)
{
	test();

	return 0;
}

int main()
{  
	printf("main thread\n");

	hMutex = CreateMutex(NULL, FALSE, NULL);  

	int i = 0;

	for(i = 0; i < 10; i++)
	{
		HANDLE handle = CreateThread(NULL, 0, ThreadFun, NULL, 0, NULL);
		CloseHandle(handle);	
	}

	getchar();

	printf("end\n");

	return 0;
}

这下可以了，每次都打印10个hello！