[PHP] about lock some codes.

[lx]

Hello:
       I have a question now.the code is:

                $ftemp = fopen("$fdoc_tmp/temp_proxy", 'w');
                fwrite($ftemp, $content);
                fclose($ftemp);

                exec("/usr/local/bin/gdnsproxy -a -f $fdoc_tmp/temp_proxy
1>$fdoc_tmp/dout 2>$fdoc_tmp/derr", $data, $ex_result);
                echo "ret=".$ex_result;

As you see, If a process run these,this is right.But two processes run this
codes.
the order maybe is:
1.process 1 create the temp_proxy1
2.process 2 create the temp_proxy2
3.process 1 exec temp_proxy2
4.process 2 exec temp_proxy2

The temp_proxy1 can't exec.

So,I want to know how to solve it.
Thank you.