GNU Info
(bfd.info)File Caching
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 `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.
`BFD_CACHE_MAX_OPEN macro'
..........................
*Description*
The maximum number of files which the cache will keep open at one time.
#define BFD_CACHE_MAX_OPEN 10
`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.
`bfd_cache_lookup'
..................
*Description*
Check to see if the required BFD is the same as the last one looked up.
If so, then it can use the stream 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))
`bfd_cache_init'
................
*Synopsis*
boolean bfd_cache_init (bfd *abfd);
*Description*
Add a newly opened BFD to the cache.
`bfd_cache_close'
.................
*Synopsis*
boolean bfd_cache_close (bfd *abfd);
*Description*
Remove the BFD ABFD from the cache. If the attached file is open, then
close it too.
*Returns*
`false' is returned if closing the file fails, `true' is returned if
all is well.
`bfd_open_file'
...............
*Synopsis*
FILE* bfd_open_file(bfd *abfd);
*Description*
Call the OS to open a file for ABFD. Return the `FILE *' (possibly
`NULL') that results from this operation. Set up the BFD so that
future accesses know the file is open. If the `FILE *' returned is
`NULL', then it won't have been put in the cache, so it won't have to
be removed from it.
`bfd_cache_lookup_worker'
.........................
*Synopsis*
FILE *bfd_cache_lookup_worker(bfd *abfd);
*Description*
Called when the macro `bfd_cache_lookup' fails to find a quick answer.
Find a file descriptor for ABFD. If necessary, it open it. If there
are already more than `BFD_CACHE_MAX_OPEN' files open, it tries to
close one first, to avoid running out of file descriptors.
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