Avoid race condition with Popen.send_signal

Cameron Simpson cs at zip.com.au
Mon Jan 2 23:53:07 EST 2012

On 02Jan2012 19:16, Adam Skutt <askutt at gmail.com> wrote:
| On Jan 2, 8:44 pm, Cameron Simpson <c... at zip.com.au> wrote:
| > On 02Jan2012 20:31, Devin Jeanpierre <jeanpierr... at gmail.com> wrote:
| > | > I think that catching the exception is probably the most Pythonic way.
| > |
| > | It's the only correct way.
| >
| > Indeed, but be precise - chek that it _is_ error 3, or more portably,
| > errno.ESRCH. POSIX probably mandates that that is a 3, but the symbol
| > should track the local system if it differs. Example:
| No. It is possible (however unlikely) for EPERM to be legitimately
| returned in this case.  Anything other than EINVAL should be
| interpreted as "The child process is dead".

Sure. I was more taking the line: catch and accept only the specific
errors you understand. Of course he can catch EPERM also. But any other
variant should at the least generate a warning to stderr or a log -
it is _unexpected_.

I take your point that reraising the exception may be overkill for
failed signal delivery (if that was your point). But I am arguing for
being very careful about what you silently pass as an ok thing.

| Hence why you should
| avoid sending the signal in the first place: the situations where you
| don't run the risk of possibly killing an innocent bystander are
| pretty narrow.  While unlikely on modern UNiX and Linux, IMO it's best
| to avoid the issue altogether whenever possible.

Fair enough too. But sometimes you need to nail a rogue child.

Cameron Simpson <cs at zip.com.au> DoD#743

Death is life's way of telling you you've been fired.   - R. Geis

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