dead code: NamedTemporaryDirectory

[zooko]

Looking at #2432, I noticed that NamedTemporaryDirectory​ is unused except for its unit test​.

Now, the newer version of NamedTemporaryDirectory over in pyutil has an added feature — automatically call .close() on children when shutting down — which might be useful on Windows, but probably isn't. In any case, let's remove this older and unused version of NamedTemporaryDirectory from Tahoe-LAFS.

[zooko]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/169

[Zooko <zookog@…>]

In a9b152780e3c4d875100853477a006edf49964ec/trunk:

remove dead code: NamedTemporaryDirectory?

fixes #2433

[daira]

I looked at the implementation of NamedTemporaryFile in pyutil, and I think it may not work correctly for asynchronous tests. The problem is that the NamedTemporaryFile object may go out of scope and have its __del__ method called before all of the callback/errback chains associated with the test have finished (it's possible that the closures of those callbacks/errbacks might hold on to the object for long enough, but that seems error-prone and complicated to reason about).

If we were going to add automatic cleanup, I would want it to only be triggered in the test's cleanup phase. Even that is potentially a problem for diagnosing what happened by looking at the files under _trial_temp in case of a test failure.