@section File caching
The file caching mechanism is embedded within BFD and allows
the application to open as many BFDs as it wants without
regard to the underlying operating system's file descriptor
limit (often as low as 20 open files).  The module in
@code{cache.c} maintains a least recently used list of
@code{bfd_cache_max_open} files, and exports the name
@code{bfd_cache_lookup}, which runs around and makes sure that
the required BFD is open. If not, then it chooses a file to
close, closes it and opens the one wanted, returning its file
handle.

@subsection Caching functions


@findex bfd_cache_init
@subsubsection @code{bfd_cache_init}
@deftypefn {Function} bool bfd_cache_init (bfd *abfd); 
Add a newly opened BFD to the cache.

@end deftypefn
@findex bfd_cache_close
@subsubsection @code{bfd_cache_close}
@deftypefn {Function} bool bfd_cache_close (bfd *abfd); 
Remove the BFD @var{abfd} from the cache. If the attached file is open,
then close it too.

@code{FALSE} is returned if closing the file fails, @code{TRUE} is
returned if all is well.

@end deftypefn
@findex bfd_cache_close_all
@subsubsection @code{bfd_cache_close_all}
@deftypefn {Function} bool bfd_cache_close_all (void); 
Remove all BFDs from the cache. If the attached file is open,
then close it too.  Note - despite its name this function will
close a BFD even if it is not marked as being cacheable, ie
even if bfd_get_cacheable() returns false.

@code{FALSE} is returned if closing one of the file fails, @code{TRUE} is
returned if all is well.

@end deftypefn
@findex bfd_cache_set_uncloseable
@subsubsection @code{bfd_cache_set_uncloseable}
@deftypefn {Function} bool bfd_cache_set_uncloseable (bfd *abfd, bool value, bool *old); 
Internal function to mark ABFD as either closeable or not.
This is used by bfd_check_format_matches to avoid races
where bfd_cache_close_all is called in another thread.
VALUE is true to mark the BFD as temporarily uncloseable
by the cache; false to mark it as closeable once again.
OLD, if non-NULL, is set to the previous value of the flag.
Returns false on error, true on success.

@end deftypefn
@findex bfd_cache_size
@subsubsection @code{bfd_cache_size}
@deftypefn {Function} unsigned bfd_cache_size (void); 
Return the number of open files in the cache.

@end deftypefn
@findex bfd_open_file
@subsubsection @code{bfd_open_file}
@deftypefn {Function} FILE* bfd_open_file (bfd *abfd); 
Call the OS to open a file for @var{abfd}.  Return the @code{FILE *}
(possibly @code{NULL}) that results from this operation.  Set up the
BFD so that future accesses know the file is open. If the @code{FILE *}
returned is @code{NULL}, then it won't have been put in the
cache, so it won't have to be removed from it.

@end deftypefn