(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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