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From Brian Pane <brian.p...@cnet.com>
Subject Re: [PATCH] Re: mmap_setaside?
Date Wed, 14 Nov 2001 18:55:37 GMT
Cliff Woolley wrote:

>I think the ideal situation would be if we had an apr_mmap_dup() similar
>to our apr_file_dup().  apr_file_dup() already solves this problem for
>files by ensuring that a duplicate copy of the file descriptor lives as
>long as the given pool.  apr_mmap_dup() in the case of duping into an
>ancestor pool could do exactly what we're trying to get mmap_setaside() to
>do: copy the apr_mmap_t() into the ancestor pool and tweak the cleanups.
>In the case of disjoint pools, it could do something else (what I haven't
>decided yet).  Then mmap_setaside() becomes as easy as file_setaside() is.

apr_mmap_dup() with an optimization for the ancestor-pool case sounds
good to me.  Actually, with a slight modification, I think this can
handle the non-ancestor-pool case too:
  * Create a reference count, in storage outside of any pool.  (I have
    no major reservations about doing a malloc for this, since it's quick
    compared to the mmap itself.  If it ever became a bottleneck, we could
    add a custom free list.)
  * Set the reference count to 1 when it's created, and increment in
  * In mmap_cleanup(), decrement the reference count.  If it's now zero,
    munmap, and free the struct that holds the reference count.  If the
    reference count is nonzero, do nothing.

What do you think?


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