php不能生成类似.pid的标识进程的临时文件

2. $filename = "/tmp/test_php.pid";
3. $fp = fopen($filename, 'w');
4. //unset($fp);
5. unlink($filename);
6. sleep(6);

2，C程序代码

3. #include

4. int main()

5. {
6. char *filename = "/tmp/test_c.pid";
7. FILE *fp;
8. fp = fopen(filename, "w");
9. unlink(filename);
10. sleep(6);
11. }