1@section File caching 2The file caching mechanism is embedded within BFD and allows 3the application to open as many BFDs as it wants without 4regard to the underlying operating system's file descriptor 5limit (often as low as 20 open files). The module in 6@code{cache.c} maintains a least recently used list of 7@code{BFD_CACHE_MAX_OPEN} files, and exports the name 8@code{bfd_cache_lookup}, which runs around and makes sure that 9the required BFD is open. If not, then it chooses a file to 10close, closes it and opens the one wanted, returning its file 11handle. 12 13@findex BFD_CACHE_MAX_OPEN macro 14@subsubsection @code{BFD_CACHE_MAX_OPEN macro} 15@strong{Description}@* 16The maximum number of files which the cache will keep open at 17one time. 18@example 19#define BFD_CACHE_MAX_OPEN 10 20@end example 21 22@findex bfd_last_cache 23@subsubsection @code{bfd_last_cache} 24@strong{Synopsis} 25@example 26extern bfd *bfd_last_cache; 27@end example 28@strong{Description}@* 29Zero, or a pointer to the topmost BFD on the chain. This is 30used by the @code{bfd_cache_lookup} macro in @file{libbfd.h} to 31determine when it can avoid a function call. 32 33@findex bfd_cache_lookup 34@subsubsection @code{bfd_cache_lookup} 35@strong{Description}@* 36Check to see if the required BFD is the same as the last one 37looked up. If so, then it can use the stream in the BFD with 38impunity, since it can't have changed since the last lookup; 39otherwise, it has to perform the complicated lookup function. 40@example 41#define bfd_cache_lookup(x) \ 42 ((x)==bfd_last_cache? \ 43 (FILE*) (bfd_last_cache->iostream): \ 44 bfd_cache_lookup_worker(x)) 45@end example 46 47@findex bfd_cache_init 48@subsubsection @code{bfd_cache_init} 49@strong{Synopsis} 50@example 51bfd_boolean bfd_cache_init (bfd *abfd); 52@end example 53@strong{Description}@* 54Add a newly opened BFD to the cache. 55 56@findex bfd_cache_close 57@subsubsection @code{bfd_cache_close} 58@strong{Synopsis} 59@example 60bfd_boolean bfd_cache_close (bfd *abfd); 61@end example 62@strong{Description}@* 63Remove the BFD @var{abfd} from the cache. If the attached file is open, 64then close it too. 65 66@strong{Returns}@* 67@code{FALSE} is returned if closing the file fails, @code{TRUE} is 68returned if all is well. 69 70@findex bfd_open_file 71@subsubsection @code{bfd_open_file} 72@strong{Synopsis} 73@example 74FILE* bfd_open_file (bfd *abfd); 75@end example 76@strong{Description}@* 77Call the OS to open a file for @var{abfd}. Return the @code{FILE *} 78(possibly @code{NULL}) that results from this operation. Set up the 79BFD so that future accesses know the file is open. If the @code{FILE *} 80returned is @code{NULL}, then it won't have been put in the 81cache, so it won't have to be removed from it. 82 83@findex bfd_cache_lookup_worker 84@subsubsection @code{bfd_cache_lookup_worker} 85@strong{Synopsis} 86@example 87FILE *bfd_cache_lookup_worker (bfd *abfd); 88@end example 89@strong{Description}@* 90Called when the macro @code{bfd_cache_lookup} fails to find a 91quick answer. Find a file descriptor for @var{abfd}. If 92necessary, it open it. If there are already more than 93@code{BFD_CACHE_MAX_OPEN} files open, it tries to close one first, to 94avoid running out of file descriptors. 95 96