detect spinners

[Aaron Swartz]

The most common reason web.py apps fail after launch is because there's some scenario under which they begin consuming lots of CPU for a long period of time, the GIL blocks everything, and the site fails (or becomes really slow).

web.py should have a method of detecting this and at least reporting it (so it can be fixed) if not preventing it. Right now you can't even debug these problems usually.

[Aaron Swartz (aaronsw)]

Here's some sample code that seems to accurately simulate a spinner, at least judging from my experience with them.

[Aaron Swartz (aaronsw)]

So Kragen's suggestion is to have web.application keep track of which pieces of code are being executed and make it so that at most three threads can execute the same piece of code at a time. The rest can block until a new slot opens up.

Plus, you can have it log when all three slots are full so that the code can be optimized/debugged.

[Anand Chitipothu (anandology)]

Lighttpd and Apache has mod_status which show the list of current requests along with times. That is good tool to detect spinners.