mmap resizing macosx unix

[Philip Semanchuk]

On Apr 5, 2009, at 10:28 AM, David Pratt wrote:

> Hi. I have been experimenting with mmap recently. I determined how  
> to read and write properly from it and so search and replace on  
> large files. The problem I am having is with replaces that are  
> larger than the mmap. In this instance I need to
>
> * rewind
> * resize the mmap to accomodate the text
> * move some part of the text to a new location on the mmap so the  
> new text does not overwrite the old
> * write the replacement text
>
> When I try to use resize it gives me the following error;
>
> SystemError: mmap: resizing not available--no mremap()

Hi David,
Based on experience with my posix_ipc module, ISTR that (a) resizing  
of the mmapp-ed segment happens via a call to ftruncate() (or  
os.truncate() in Python land) and (b) OS X only supports one call to  
this per segment; subsequent calls fail. Keep in mind that I was  
dealing with shared memory.  A regular mmapped file might resize just  
fine so point (b) might be irrelevant for you.

HTH
Philip