96 lines
3.0 KiB
Plaintext
96 lines
3.0 KiB
Plaintext
@section File caching
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The file caching mechanism is embedded within BFD and allows
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the application to open as many BFDs as it wants without
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regard to the underlying operating system's file descriptor
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limit (often as low as 20 open files). The module in
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@code{cache.c} maintains a least recently used list of
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@code{BFD_CACHE_MAX_OPEN} files, and exports the name
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@code{bfd_cache_lookup}, which runs around and makes sure that
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the required BFD is open. If not, then it chooses a file to
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close, closes it and opens the one wanted, returning its file
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handle.
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@findex BFD_CACHE_MAX_OPEN macro
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@subsubsection @code{BFD_CACHE_MAX_OPEN macro}
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@strong{Description}@*
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The maximum number of files which the cache will keep open at
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one time.
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@example
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#define BFD_CACHE_MAX_OPEN 10
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@end example
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@findex bfd_last_cache
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@subsubsection @code{bfd_last_cache}
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@strong{Synopsis}
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@example
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extern bfd *bfd_last_cache;
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@end example
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@strong{Description}@*
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Zero, or a pointer to the topmost BFD on the chain. This is
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used by the @code{bfd_cache_lookup} macro in @file{libbfd.h} to
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determine when it can avoid a function call.
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@findex bfd_cache_lookup
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@subsubsection @code{bfd_cache_lookup}
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@strong{Description}@*
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Check to see if the required BFD is the same as the last one
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looked up. If so, then it can use the stream in the BFD with
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impunity, since it can't have changed since the last lookup;
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otherwise, it has to perform the complicated lookup function.
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@example
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#define bfd_cache_lookup(x) \
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((x)==bfd_last_cache? \
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(FILE*) (bfd_last_cache->iostream): \
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bfd_cache_lookup_worker(x))
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@end example
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@findex bfd_cache_init
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@subsubsection @code{bfd_cache_init}
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@strong{Synopsis}
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@example
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bfd_boolean bfd_cache_init (bfd *abfd);
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@end example
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@strong{Description}@*
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Add a newly opened BFD to the cache.
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@findex bfd_cache_close
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@subsubsection @code{bfd_cache_close}
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@strong{Synopsis}
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@example
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bfd_boolean bfd_cache_close (bfd *abfd);
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@end example
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@strong{Description}@*
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Remove the BFD @var{abfd} from the cache. If the attached file is open,
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then close it too.
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@strong{Returns}@*
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@code{FALSE} is returned if closing the file fails, @code{TRUE} is
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returned if all is well.
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@findex bfd_open_file
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@subsubsection @code{bfd_open_file}
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@strong{Synopsis}
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@example
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FILE* bfd_open_file (bfd *abfd);
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@end example
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@strong{Description}@*
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Call the OS to open a file for @var{abfd}. Return the @code{FILE *}
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(possibly @code{NULL}) that results from this operation. Set up the
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BFD so that future accesses know the file is open. If the @code{FILE *}
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returned is @code{NULL}, then it won't have been put in the
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cache, so it won't have to be removed from it.
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@findex bfd_cache_lookup_worker
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@subsubsection @code{bfd_cache_lookup_worker}
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@strong{Synopsis}
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@example
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FILE *bfd_cache_lookup_worker (bfd *abfd);
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@end example
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@strong{Description}@*
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Called when the macro @code{bfd_cache_lookup} fails to find a
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quick answer. Find a file descriptor for @var{abfd}. If
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necessary, it open it. If there are already more than
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@code{BFD_CACHE_MAX_OPEN} files open, it tries to close one first, to
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avoid running out of file descriptors.
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