Saturday, March 05

Geek

Looking At Lupa

I'm doing some testing on Lupa:

Calling a LuaJIT function from Python: 363ns
Calling a Python function from LuaJIT: 447ns
Calling a LuaJIT function from Psyco: 253ns
Calling a Psyco function from LuaJIT: 730ns
Calling a Python function from Python: 177ns
Calling a Pysco function from Psyco: 3ns (!)

I also tested some sample code that calls a Lua function from Python and passes it a Python function as a parameter; that takes bout 1.8µs in Python and 2.1µs in Psyco (jumping into and out of the JIT clearly has some overhead).

The worst case, unfortunately, is likely to be the most common one - calling back to Python/Psyco (specifically the Minx API) to get data for the Lua script.  Lupa has some nice wrappers for using data structures rather than functions, so I'm going to see how they go.

That said, the worst case is 730 nanoseconds.

The one hiccup is that creating a Lupa LuaRuntime instance leaks about 30kB, and crashes Python after 13,000 to 15,000 instances - even if I force garbage collection.  I've posted that to the Lupa mailing list, and will follow up and see if I can help find the problem and fix it.

That can be solved using a worker pool on the web server, with worker processes being retired after (say) 100 requests.  The overhead on the server would be quite small, it would make for much better scalability, and would keep potentially buggy libraries or library use under control.  (A careless PIL call can use a huge amount of memory.)

Update: The author has fixed the problem and released a new version of Lupa (0.19) - on the weekend.  It now works flawlessly.

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