Multiple Image-Upload broken when SessionHandlerRedis is installed

[tiefenb]

I got a very strange bug in my system:

One week after switching from SessionHandlerDB to SessionHandlerRedis, the costumer reported that uploading multiple images in parallel are broken. After searching the bug some hours in other modules, core and some hooks which I use, I begann to deactivate each third-party module to test the uploading. After deactivating SessionHandlerRedis the upload was working correct.

Do you have any idea why SessionHandlerRedis causes this bug?

What exactly happens is:
I upload 1 image (abc.jpg) with 2000KB and 1 image with (xyz.jpg) with 200 KB.
The first row in the database-table what I see is the row with xyz.jpg and after the other image is finished with the upload the xyz.jpg row is deleted and only the abc.jpg is saved.

Processwire: 3.0.122
PHP: 7.0

I will try to reproduce this with a fresh and empty PW installation and SessionHandlerRedis soon.

[tiefenb]

Now I have tested it with a clean installation of PW 3.0.124 (site-default), PHP 7.0.31 and SessionHandlerRedis.

after installing SessionHandlerRedis the paralell uploading doesn't work any more :-(

[tiefenb]

I have zipped my installation and you can download it here: https://wetransfer.com/downloads/0d89567ece797bc755514df5a2c3fa7220190119210112/7fcbc5926afa1e5c07864f681f98271220190119210112/238d77

if you want to run it with docker go into the root directory of pw:

docker-compose build
docker-compose up

sql dump is also in the root: pwtest_dump.sql

[tiefenb]

okay this bug appear also with native redis AND memcached as php session handler. I will close this issue because I think this is a general processwire or PHP bug: processwire/processwire-issues#798