[Numpy-discussion] memmap close() and flush()

Sebastian Haase seb.haase at gmx.net
Wed Jan 31 17:07:15 EST 2007

On 1/31/07, Fernando Perez <fperez.net at gmail.com> wrote:
> On 1/31/07, Travis Oliphant <oliphant at ee.byu.edu> wrote:
> > Fernando Perez wrote:
> > I don't know.  If you have other things pointing to it, should you
> > really close it?
> Well, it's like a file: you can close it because you've decided it's
> time to close it, and I think it's better that other references get an
> exception if they try to write to it when they shouldn't:
> In [2]: file1 = open('foo','w')
> In [3]: file1.write('Some text')
> In [4]: file2 = file1
> In [5]: file1.close()
> In [6]: file2.write("I'm not the original owner but I'll try to write anyway")
> ---------------------------------------------------------------------------
> exceptions.ValueError                                Traceback (most
> recent call last)
> /home/fperez/<ipython console>
> ValueError: I/O operation on closed file
> This seems like the right API to me.
> > At any rate you have access to the mmap file through the _mmap
> > attribute.  So, you can always do
> >
> > self._mmap.close()
> I don't like an API that encourages access to internal semi-private
> members, and it seems to me that closing the object is a reasonably
> top-level operation whose impmlementation details (in this case the
> existence and name of the _mmap member) should be encapsulated out.
> Cheers,
> f

After asking this question rather for acedemical reasons, I now
realize that I indead must have a "somehow dangling" (i.e. not
deleted) reference problem.

I create my Medical-Image-File-class object on a 400MB file repeatedly
(throwing the result away)  and after 5 calles I get:
  File "/jws30/haase/PrLinN/Priithon/Mrc.py", line 55, in __init__
    self.m = N.memmap(path, mode=mode)
  File "/home/haase/qqq/lib/python/numpy/core/memmap.py", line 67, in __new__
    mm = mmap.mmap(fid.fileno(), bytes, access=acc)
EnvironmentError: [Errno 12] Cannot allocate memory

Calling gc.collect()  seams to clean things up and I can create 4-5
times afterwards, before running out of memory space again.

Note: My code is based on code that was tested and worked using numarray.


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