Add test for preexec_fn fd double close issue

[fantix]

Refs #466

[fantix]

@graingert may I ask for a review pls?

[graingert]

@graingert may I ask for a review pls?

Just doing a eyeball pass at the moment - will do a proper review later. My gut feeling is that I think it's a bit complicated using a thread pool executor and a queue and a pipe and an event so I'll see if I can have a ponder on making this simpler - eg just using threading.Barrier

[graingert]

@graingert may I ask for a review pls?

Just doing a eyeball pass at the moment - will do a proper review later. My gut feeling is that I think it's a bit complicated using a thread pool executor and a queue and a pipe and an event so I'll see if I can have a ponder on making this simpler - eg just using threading.Barrier

ok I think I've managed to simplify this a lot: https://github.com/MagicStack/uvloop/pull/481/files#r924838769

[fantix]

Close in favor of #481