[Python-Dev] PEP 446: Add new parameters to configure the inherance of files and for non-blocking sockets (original) (raw)

Cameron Simpson cs at zip.com.au
Fri Jul 5 07:20:36 CEST 2013

On 05Jul2013 10:41, I wrote: | On 04Jul2013 13:03, Victor Stinner <victor.stinner at gmail.com> wrote: | | Other Changes | | ------------- | | The subprocess.Popen class must clear the close-on-exec flag of file | | descriptors of the passfds parameter. || I would expect Popen and friends to need to both clear the flag to | get the descriptors across the fork() call, and possibly to set | the flag again after the fork. Naively, I would expect the the flag | to be as it was before the Popen call, after the call.

This is harder than I'd thought through.

Descriptors go across a fork() anyway, and after an exec() there is nobody to change their state.

In order for the parent to restore the prior close-on-exec state (if deemed the right thing to do) it would need to know when the exec was done in the child.

You'd need something like an extra descriptor attached to a pipe marked close-on-exec so that the parent could see EOF on the read end after the exec, since the exec would close the write end. tractable, but baroque.

So I'd have the PEP take a position on the post-exec() state of the passed file descriptors, and if state is not going to be restored it should outright say that passing an fd clears the close-on-exec flag. Which is it does, but I think the doco should be pretty overt about:

If you decide state should get restored, the implementation gets a bit fiddlier to detect the exec() in the child. I can't speak for what might be required on non-UNIX.

Cheers,

Cameron Simpson <cs at zip.com.au>

Agree, for Law is costly. -- Very good advice to litigious Persons, founded upon Reason and Experience; for many Times the Charges of a Suit exceed the Value of the Thing in Dispute. - Bailey's dictionary, 1736

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