Question

Ok, ok .. so right now I’m freaking out.

index1.php

<?
function write_file($filepath,$filecontent) {
    $openedfile = fopen($filepath,"w+"); //replace with $openedfile = fopen($filepath,"a"); just in case
    flock($openedfile, LOCK_EX);
//add here fclose($openedfile); to work
//add here $openedfile = fopen($filepath,"w+"); to work
    fwrite($openedfile,$filecontent);
    flock($openedfile, LOCK_UN);
    fclose($openedfile);
}
function read_file($filepath) {
    $openedfile = fopen($filepath,"r+");
    flock($openedfile, LOCK_SH);
    sleep(10);
    $filecontent = file_get_contents($filepath);
    flock($openedfile, LOCK_UN);
    fclose($openedfile);
    return $filecontent;
}
write_file("Readme.txt","test 1");
$f1 = read_file("Readme.txt");
echo $f1;
?>

index2.php

<?
function write_file($filepath,$filecontent) {
    $openedfile = fopen($filepath,"w+"); //replace with $openedfile = fopen($filepath,"a"); to work
    flock($openedfile, LOCK_EX);
//add here fclose($openedfile); to work
//add here $openedfile = fopen($filepath,"w+"); to work
    fwrite($openedfile,$filecontent);
    flock($openedfile, LOCK_UN);
    fclose($openedfile);
}
function read_file($filepath) {
    $openedfile = fopen($filepath,"r+");
    flock($openedfile, LOCK_SH);
    $filecontent = file_get_contents($filepath);
    flock($openedfile, LOCK_UN);
    fclose($openedfile);
    return $filecontent;
}
write_file("Readme.txt","test 2");
$f1 = read_file("Readme.txt");
echo $f1;
?>

I run index1.php, then after 2 sec I run index2.php. Index2.php waits for index1.php as expected but index1.php shows nothing after 10 sec, while index2.php shows “test 2”.
What is going on?

EDIT: I figured it out :D. I changed

$openedfile = fopen($filepath,"w+");

to

$openedfile = fopen($filepath,"a");

in second php and it doesn’t wipe readme.txt upon index2.php execution anymore.

Answer 1

Doesn’t this has to do something with the fact your readme.txt is actually empty for a very short period of time when you open the file to write in it? I thought PHP took out the entire text, and than replaced it with the entire text + addings. When index1.php wants to read the file, index2.php has just cleared it perhaps? You can check this in the apache logs by the way.

EDIT: also, immediately after unlocking the file, index2.php takes control over it, overwriting TEST 1 with TEST 2.