[Patches] [ python-Patches-1529142 ] Allowing multiple instances of IDLE with sub-processes

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Wed Feb 7 08:49:03 CET 2007


Patches item #1529142, was opened at 2006-07-26 20:45
Message generated for change (Comment added) made by taleinat
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Category: IDLE
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Tal Einat (taleinat)
Assigned to: Kurt B. Kaiser (kbk)
Summary: Allowing multiple instances of IDLE with sub-processes

Initial Comment:
(See patch 1201569 "allow running multiple instances of
IDLE" for previous discussion on this topic)

To summarize discussion up to this point: There is a
problem doing this on Windows since more than one
listening socket can be openned on a single port.

I suggest we "dodge" the Windows problem for now by
having IDLE try a random port every time (like in the
IDLEfork patch 661363) - thus collisions will be kept
to a minimum. If we choose among over 10,000 ports,
most users will never encounter a port collision. And
even when a collision does happen, it will probably be
detected and properly dealt with - collision
non-detection errors are, as Kurt mentioned, erratic.


This patch chooses a port from range(49152, 65536),
which are the 'dynamic' ports as described by the DCCP
(see http://www.iana.org/assignments/port-numbers), and
avoids known 'dangerous' ports (used by trojans, worms,
etc.) which I gathered by Googling for half an hour.

I replaced socket.timeout with select(), since I find
its timeout mechanism is more reliable. (Currently,
Python's socket's timeout mechanism raises unexpected,
unexplained errors on Windows.)

I also changed the flow a bit, so if a timeout occurs
after a sub-process is spawned, the subprocess is killed.

IMO This requires thorough testing. I tested it for
half an hour on my WinXP Python2.4.3, and after fixing
typos and such, everything seems to work.

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>Comment By: Tal Einat (taleinat)
Date: 2007-02-07 09:49

Message:
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After removing the SO_REUSEADDR flag, this has been working without any
pauses, delays or hitches on my WinXP Python2.5 install. I sometimes have
as many as 8 separate instances of IDLE running in parallel, with no side
effects.

About the SO_REUSEADDR flag, I'm wondering if this is still required on
Posix systems now that we're choosing random ports. If so, we should choose
whether to use this flag based on the OS.

Is there any good reason -not- to choose a random port? I can't think of
any.

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