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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
cache.c
maintains a least recently used list of
BFD_CACHE_MAX_OPEN
files, and exports the name
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.
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BFD_CACHE_MAX_OPEN macro
Description
The maxiumum number of files which the cache will keep open at
one time.
#define BFD_CACHE_MAX_OPEN 10
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bfd_last_cache
Synopsis
extern bfd *bfd_last_cache;
Description
Zero, or a pointer to the topmost BFD on the chain. This is
used by the bfd_cache_lookup
macro in ‘libbfd.h’ to
determine when it can avoid a function call.
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bfd_cache_lookup
Description
Checks to see if the required BFD is the same as the last one
looked up. If so then it can use the iostream in the BFD with
impunity, since it can’t have changed since the last lookup,
otherwise it has to perform the complicated lookup function
#define bfd_cache_lookup(x) \ ((x)==bfd_last_cache? \ (FILE*)(bfd_last_cache->iostream): \ bfd_cache_lookup_worker(x))
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bfd_cache_init
Synopsis
void bfd_cache_init (bfd *);
Description
Initialize a BFD by putting it on the cache LRU.
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bfd_cache_close
Description
Remove the BFD from the cache. If the attached file is open,
then close it too.
Synopsis
void bfd_cache_close (bfd *);
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bfd_open_file
Description
Call the OS to open a file for this BFD. Returns the FILE *
(possibly null) that results from this operation. Sets up the
BFD so that future accesses know the file is open. If the FILE
returned is null, then there is won’t have been put in the
cache, so it won’t have to be removed from it.
Synopsis
FILE* bfd_open_file(bfd *);
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bfd_cache_lookup_worker
Description
Called when the macro bfd_cache_lookup
fails to find a
quick answer. Finds a file descriptor for this BFD. If
necessary, it open it. If there are already more than
BFD_CACHE_MAX_OPEN files open, it trys to close one first, to
avoid running out of file descriptors.
Synopsis
FILE *bfd_cache_lookup_worker(bfd *);
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