Import lock bug

[tomprince]

Given sample.py:

from crochet import setup, wait_for_reactor
setup()

from twisted.names.client import lookupAddress

answers, _, _ = wait_for_reactor(lookupAddress)('google.com')

print [
    record.payload.dottedQuad()
    for record in answers
    ]

Running python sample.py finished instantly, but python -c 'import sample fails.

I suspect this might have something to do with the import lock.

[tomprince]

Simpler case:

from crochet import setup, wait_for_reactor
setup()
wait_for_reactor(__import__)('sys')

[itamarst]

I wonder if this is something Crochet can even solve. My first thought is documenting that one shouldn't run wait_for_reactor and friends on module level.

[tomprince]

... or anything called at module level.

[itamarst]

Perhaps EventualResult.wait() should throw an exception if imp.lock_held() is true.

[itamarst]

In Python 3.3 (which is minimal supported version anyway) "The locking scheme has changed to per-module locks for the most part. A global import lock is kept for some critical tasks, such as initializing the per-module locks." Which means simply checking imp.lock_held() is insufficient on Python 3, though to be fair deadlocks are much less likely there. I'll probably just punt Python 3 support to another ticket.