Issue http://bugs.python.org/issue1663329 details an annoyance in the subprocess module that has affected several users, including me. Essentially, closing hundreds of thousands of file descriptors by round-tripping through the python exception machinery is very slow, taking hundreds of milliseconds and at times many seconds. The proposed fix is to write this loop in c. The c function is but a handful of lines long. I purposefully kept the implementation trivial so that it will work on all unix variants (there is another issue that contains a super-duper optimization for AIX, and other possibilities exist for Solaris, but the simple fix yields a ten-fold speedup everywhere but windows, so I didn't think that it was worth the complexity). Though technically relating only to performance, I consider this a bug-fix candidate as mysterious multi-second delays when launching a subprocess end up making the functionality of close_fds unusable on some platform configurations (namely, those with high MAX_FD set). It would be great to see this is 2.5.2. Understanding that issue evaluation takes significant effort, I've done some evaluation/triage on other open tickets: ---------------------------------------- See issues for detailed comments. http://bugs.python.org/issue1516330: No clear problem, invalid patch. Recommend rejection. http://bugs.python.org/issue1516327: No clear problem, no patch. Recommend closing. http://bugs.python.org/issue1705170: reproduced. Conjecture as to why it is occurring, but I don't know the guts well enough to propose a decent fix. http://bugs.python.org/issue1773632: tested patch. Recommend accepting unless there are things I don't know about this mysterious _xmlrpclib extension (which there doubtlessly are) http://bugs.python.org/issue738948: Rather old PEP that has gathered no comments. Calling it a "PEP" is generous--it is really just a link to an academic paper with a note about how this might be integrated into Stackless. Thanks, -Mike