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Re: [ISSUE] Cancelling svn checkout leaves an open file handle

From: Daniel Sahlberg <daniel.l.sahlberg_at_gmail.com>
Date: Wed, 9 Sep 2020 08:18:02 +0200

Den ons 9 sep. 2020 kl 06:44 skrev Nathan Hartman <hartman.nathan_at_gmail.com

> On Tue, Sep 8, 2020 at 6:08 AM Uroš Jovanović <urosh3d_at_gmail.com> wrote:
> >
> > Then, mid downloading some of the larger files a temp file will appear
> in .svn\tmp. Once that happens, hit the Cancel button.
> > It will signal the cancellation to the svn client and it will throw the
> SvnOperationCanceledException, the SvnClient gets disposed BUT an open file
> handle remains on ".svn\tmp\svn-XYZ123" file.
> > If you try to delete it, Windows will complain that it is used by our
> test app. :(
> Moving this to the dev@ list...
> Potentially long-running APIs such as 'checkout' allow the client to
> provide a 'cancel_func' callback, which is called at various strategic
> places to ask the client whether the operation should be canceled.
> It sounds to me like one of those places sees a cancel request and
> returns to its caller, forgetting to do some cleanup.
> Last night I tried to find such a place by reading code.
> The 'checkout' command sets up a working copy (if necessary) and then
> calls the 'update' logic to do the heavy lifting.
> The 'update' logic is quite involved as it handles all sorts of
> possibilities, which means the number of branches of the call tree
> that need to be checked are too numerous for my code reading approach
> to be sensible.
> My thoughts for an automated approach, provided there is a way for a
> process to inquire how many open file handles it has (I assume there
> is a way; I've just never had to do this): The idea is to write a
> minimal client that does the following (on a ramdrive):
> 1. Check out a working copy of a repository, giving a cancel_func 'A'
> that increments a global variable 'n' each time it is called and
> always returns "don't cancel."
> 2. Loop n times, the loop counter being a global variable 'x':
> 2.1: Delete the working copy.
> 2.2: Check out a working copy of the same repository, giving a
> different cancel_func 'B' that returns "don't cancel" the
> first (x - 1) times it is called, and returns "cancel" the
> x-th time it is called.
> 2.3: Test whether there are open file handles. If there are, we
> know at which iteration the cleanup is not done, and we break
> out of the loop.
> 3. If x >= n, quit; we didn't find the problem.
> 4. Delete the working copy.
> 5. Check out a working copy of the same repository, giving a different
> cancel_func 'C' that returns "don't cancel" the first (x - 1) times
> it is called, and traps the x-th time it is called, allowing the
> call stack to be examined.
> Notes and caveats:
> 1. This could run for days (or years).
> 2. Then again, if it can be exposed pretty reliably by a user hitting
> a Cancel button in a GUI, that means cancel_func is called
> frequently enough from the offending location that it should
> (hopefully) be caught relatively soon in the process.
> 3. I think a huge repository isn't needed. The Greek Tree used by the
> test suite may suffice. If it doesn't expose the bug, I'd retry
> with a larger file thrown in. If that doesn't expose it, add
> increasing complexity such as externals, etc.
> 4. This relies on the logic being executed identically for each
> checkout (i.e., cancel_func is called the same number of times from
> the same call sites).
> 5. No idea how this could be turned into a regression test.
> 6. If there's a better way, I'd love to hear it!

For a regression test (as well as trying to pinpoint what goes wrong),
wouldn't it be enough if the cancel_func check for the presence of a file
in .svn/tmp (maybe even checking if it is open - in Linux that should be
easy enough to check in /proc/$PID/fd) and then signal to cancel. That
would "only" need a repository/file that is large enough to trigger calling
the cancel_func.

I checked quickly and I also see the open file when checking out using
TortoiseSVN and cancelling and it seems to occur all the time.

Kind regards
Received on 2020-09-09 08:18:20 CEST

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