PHP directory exist check problems - php

Question

I have a problem when I create a new directory with PHP when uploading a file.
The directory is created, but if another instance of the same script runs at the same time the directory exist check doesn't work correctly (gives PHP warning).
Someone told me it's a race condition but I still have this issue after adding some random sleep time.
usleep(mt_rand(1, 50));
if(!is_dir($dir)){
mkdir($dir);
}
usleep(mt_rand(1, 50));
can anyone help?
Does anybody know a safe way to upload a file in multiple parts, with 3-4 parts being uploaded at the same time? Currently I'm moving the uploaded parts in a temporary directory (is_dir fails on the temporary dir if more parts arrive at the same time), then when the number of files from that dir equal the number of parts the parts get combined. But it fails many times, sometimes is_dir gives warning, sometimes the parts get combined twice...

Answer 1

mkdir() returns true on success, and false on failure (dir already exists). So you can just use it as a part of your conditional check.
if (!is_dir($dir) && mkdir($dir)) {
// good to go
}

Answer 2

You want to use clearstatcache() at the top of the page testing for the directory, so that the system cache of current directory structure is fresh. read more here
The upload javascript splits the file in multiple parts and sends 4 ajax requests to php, so the php receives 4 parts simultaneously. when all parts are received the php should combine them to reproduce the file on the server
So why split them up, send the Ajax as a single request and then allow PHP to handle each blob file part in its own scripting. This will sidestep the problem. PHP - with the correct setting up - can comfortably handle large files in chunk blocks.