I'm trying to write code that will reproduce the Concurrent Requests limit (10 requests longer than 5 seconds, described here: https://developer.salesforce.com/blogs/engineering/2013/05/force-com-concurrent-request-limits.html). This is so I can judge how likely the error is, and how if will impact our users. So far I have not been able to cause the error to happen.
My attempt was to make a Visual Force page with a button (up to 12 buttons) that would execute a controller method that was guaranteed to run for about 10 seconds of clock time. For the 10 second delay, I used Dan Appleman's concurrency class (see Reproduce UNABLE_TO_LOCK_ROW error and his 2nd edition Advanced Apex book).
But no matter how many times, or how rapidly, I click the VF button(s), the debug logs always show a long series of successful 10+ second logs. I tried one button, 12 buttons,and 1 button across many tabs. In all cases the logs group the controller actions into sets of 6 parallel events, with a large gap between the sets. So, 6 logs are produced with roughly identical start-times, then there is a gap of up about 10 seconds (which matches the delay in the controller), and then another set of 6 logs are generated.
I'm asking for an explanation of why this approach doesn't work. I think that VF is governing how many synchronous requests it will send out, but I can't find documentation on that...? Additionally, I'm asking for a successful approach to generating/demoing the Concurrent Request Limit.