[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
Sun Jul 7 02:29:12 CEST 2013

On 06Jul2013 14:43, Victor Stinner <victor.stinner at gmail.com> wrote: | 2013/7/6 Cameron Simpson <cs at zip.com.au>: | > Yes. Please forget I mentioned fork(); it is only relevant if you | > were offering some facility to undo the addition of cloexec to a | > Popen passed file descriptor. Which you are not. || Oh... gotcha. I now understood your concern. || There is a little "trick" here: at fork, file descriptors are | duplicated in the child process and almost all properties (open state, | flags, offset, etc.) are shared. There is one little exception: file | attributes are not shared, and there is only one file attribute: | OCLOEXEC. Setting OCLOEXEC in a child process does not affect the | flag in the parent process ;-) I will add a unit test to check this.

That's news to me. Interesting.

I can't find UNIX doco to support this, though I haven't finished looking. None of the POSIX, Linux or MacOSX fork() manual pages seem to describe this.

Can you point me at doco for this? I thought file descriptors were a direct index into a per-process table of file handle structures, and did not think the latter got part copies, part shared over a fork.

Also, is O_CLOEXEC really the only file attribute? So O_NONBLOCK is a flag and not an attribute (guessing the terminology distinguishes these)? Now you mention it, ISTR noticing that there were distinct ioctls to adjust flags and something else.

| I modified the PEP to explain that, and I also mentioned the name of | the close-on-exec and blocking flags: | http://hg.python.org/peps/rev/425f831fddf7

Thanks.

Your change says:

On Windows, the close-on-exec flag is HANDLE_FLAG_INHERIT.

I feel it would be clearer to say:

On Windows, the close-on-exec flag is the inverse of HANDLE_FLAG_INHERIT.

or

On Windows, the close-on-exec flag implemented using HANDLE_FLAG_INHERIT.

(This latter is fine because the rest of the paragraph explains the meaning of HANDLE_FLAG_INHERIT.)

The bare "is" in your current wording suggests to me that the truthiness (ick!) of close-on-exec is the same as for HANDLE_FLAG_INHERIT, which it isn't.

Cameron Simpson <cs at zip.com.au>

I've always been a big Greenaway fan - I've seen and enjoyed "The Falls" for crying out loud. - Peter Alexander Merel <pete at extro.ucc.su.OZ.AU>

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