Overselling - 10 items in stock, 30 sold.

Hello.

I've been testing the module to see if the overselling problem (which has been an issue for Drupal modules in the past) is an issue with Commerce/Commerce Stock.

To test I've written a JMeter test script. I've been sending 50 threads (users), with 20s ramp up period, to a local install, checking out with the example payment method, setting 10 items as in stock - I am typically finding it will sell around 30 item, and the stock count after the test script has run will be between -1 and 4. I've tested with commerce stock 7.x-2.0-alpha2, and 7.x-2.x-dev, the results are the same.

I see this as two different (but related) problems:
1) The stock count becomes out of sync with the number of items sold - it is selling 30 items, and the stock count is only decreased by 6-11.
2) Once the stock hits 0, it still sells items if the payment is already in process.

It is likely that different problems will be found with different payment gateways, and the test script will need to be modified to test different payment gateways.

I've attached the test script here - to use it you'll need to download JMeter (http://jmeter.apache.org/). In the User Defined Variable section at the top of the test script you'll be able to define the product URL/ID, the site URL, and optionally a port number. You can also change the number threads and the ramp up period under the Commerce Stock Overselling Test Thread options. The setting in the script demonstrate the problem well on my machine, but may need to be tweaked, depending on how powerful your machine is - if I change the ramp up period to 10s, it hardly oversells at all, as it responds 500 to most of the requests, and if I change it to 30s, it oversells less as there are less collisions.

Any ideas?

Thanks,
Chris.