[issue12187] subprocess.wait() with a timeout uses polling on POSIX
STINNER Victor
report at bugs.python.org
Wed Jan 29 00:55:56 CET 2014
STINNER Victor added the comment:
The new asyncio module doesn't have this performance issue: it allows to wait asynchronously for the process exit without busy loop.
Right now, there is no high-level API for that, but it is very likely that Python 3.4 final will provide a simple proc.wait() method for that. See #20400 and related Tulip issue:
http://code.google.com/p/tulip/issues/detail?id=115
On Unix, the default implementation sets an handler for SIGCHLD signal which calls waitpid(pid, WNOHANG) on all processes to detect process exit. But it has also a faster implementation which calls waitpid(-1, WNOHANG) only once.
asyncio uses signal.set_wakeup_fd() to wake up its event loop when it gets a signal.
Charles-François wrote:
> Honestly, I think the extra complexity and non-portability isn't worth it.
I agree. And any change may break the backward compatibility, because signal handling is tricky and many detail are platform specific.
asyncio is well designed and solves this issue in a portable way. On Windows, RegisterWaitWithQueue() is used with an overlapped object and a proactor event loop to wait for the process exit.
I leave the issue open until all the new subprocess code is merged into Tulip and Python asyncio.
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nosy: +gvanrossum
versions: +Python 3.4 -Python 3.3
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