Q:

Does PHP offer file concurrency in this scenario?

I have a cache file that is updated every hour or so. The file size ranges from 100KB to 1MB. The way the cache is updated is with the file_put_contents() method.
Only the server writes to the file. However, there is continuous access to the file. The file is accessed by users by a script that performs a one time read through readfile() to echo it to the user.
If the file is being read by the caching script, and the server runs the user reading script, or the other way around, would there be a problem? Or is this handled automatically by PHP>

A:

Basically, you should lock the file while writing or reading. At least, it guarantees that there is no problem. It is the way of good programming!. The example is shown below.
<?php

$fp = fopen("/tmp/lock.txt", "w+");

if (flock($fp, LOCK_EX)) { // do an exclusive lock
    fwrite($fp, "Write something here\n");
    flock($fp, LOCK_UN); // release the lock
} else {
    echo "Couldn't lock the file !";
}

fclose($fp);

?>

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