Memory leaking when using Bazaar branches

[John Arbash Meinel]

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Nicholas Allen wrote:
> Hi,
> 
> I am not an expert Python programmer by any means but I think there may be 
> bugs in the Bazaar API that cause cyclic references and hence some memory not 
> to be freed. Every time my email tool sends an email it seems to loose a bit 
> of memory. I'm not sure how to debug this as I am fairly new to Python.
> 
> Of course it may be the way I'm using the API that is wrong. If anyone can 
> offer hints on possible gotchas in the Bazaar API that could lead to this I 
> would be very grateful.
> 
> Cheers,
> 
> Nick
> 

There was a recent patch from Michael Hudson, I believe, which found a
reference cycle from LockableFiles (which has a __del__ and thus can't
be cyclically gc'd), and moved the __del__ into a helper.

We rarely use __del__, so even with a ref cycle the python gc can
usually clean things up. Using a grep, the ones I find are:

bzrlib/atomicfile.py:124:    def __del__(self):
bzrlib/lock.py:135:    def __del__(self):
bzrlib/lockable_files.py:112:    def __del__(self):
bzrlib/smart/medium.py:655:    def __del__(self):
bzrlib/transport/memory.py:292:    def __del__(self):
bzrlib/transport/sftp.py:119:    def __del__(self):


For memory and sftp, they are lock clases, which are rarely used today
(there were only for pre 0.8.2 format branches). And 'memory' is only
used in the test suite.

Atomicfile shouldn't ever be part of a ref cycle, as it is never really
given something else to handle (just a file descriptor).

As mentioned, LockableFiles probably needs to be fixed.

The one in 'bzrlib/smart/medium.py' is a bit curious. As that does
maintain stuff like "_request". I don't know whether there are cycles or
not, just that it is a more involved class, and thus more likely to run
into problems.

Anyway, just merging Michael's patch should probably be enough.

John
=:->
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