Suddenly starting to leave Zombies is NOT an option for me. To prevent zombies, all applications using the subprocess module would need to be changed. This is a major breakage of backwards compatibility, IMHO. subprocess (as well as the popen2 module) has prevented zombies automatically from the beginning and I believe they should continue to do so (at least by default). 

A little bit of history: When I wrote the subprocess module, I stole the idea of calling _cleanup whenever a new instance is created from the popen2 module, since I thought it was nice, lightweight and avoided having a __del__ method (which I have some bad experience with, GC-related). This worked great for a long time. At 2006-04-10, however, martin.v.loewis committed patch 1467770 (revision r45234), to solve bug 1460493. It introduces a __del__ method and some more complexity. I must admit that I didn't review this patch in detail, but it looked like thread safeness was being taken care of. But apparently it isn't. 

Perhaps reverting to the original popen2 approach would solve the problem? Or does the popen2 module suffer from this bug as well? 

I think that we need to fix this once and for all, this time. We should probably also consider adding the option of not having subprocess auto-wait while we are at it, for those what would like to wait() themselves (there should be a tracker item for this, but I can't find it right now). 

Are we tight on time for fixing this bug? I'm out in the forest right now...