thodg/libgit2/src/odb.h

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• Hash : c6ac28fd
  Author :
  Date : 2012-09-10T12:24:05
  

  Reorg internal odb read header and object lookup
  
  Often `git_odb_read_header` will "fail" and have to read the
  entire object into memory instead of just the header.  When this
  happens, the object is loaded and then disposed of immediately,
  which makes it difficult to efficiently use the header information
  to decide if the object should be loaded (since attempting to do
  so will often result in loading the object twice).
  
  This commit takes the existing code and reorganizes it to have
  two new functions:
  
  - `git_odb__read_header_or_object` which acts just like the old
    read header function except that it returns the object, too, if
    it was forced to load the whole thing.  It then becomes the
    callers responsibility to free the `git_odb_object`.
  - `git_object__from_odb_object` which was extracted from the old
    `git_object_lookup` and creates a subclass of `git_object` from
    an existing `git_odb_object` (separating the ODB lookup from the
    `git_object` creation).  This allows you to use the first header
    reading function efficiently without instantiating the
    `git_odb_object` twice.
  
  There is no net change to the behavior of any of the existing
  functions, but this allows internal code to tap into the ODB
  lookup and object creation to be more efficient.
  

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• src/odb.h

• /*
   * Copyright (C) 2009-2012 the libgit2 contributors
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  #ifndef INCLUDE_odb_h__
  #define INCLUDE_odb_h__
  
  #include "git2/odb.h"
  #include "git2/oid.h"
  #include "git2/types.h"
  
  #include "vector.h"
  #include "cache.h"
  #include "posix.h"
  
  #define GIT_OBJECTS_DIR "objects/"
  #define GIT_OBJECT_DIR_MODE 0777
  #define GIT_OBJECT_FILE_MODE 0444
  
  /* DO NOT EXPORT */
  typedef struct {
  	void *data;			/**< Raw, decompressed object data. */
  	size_t len;			/**< Total number of bytes in data. */
  	git_otype type;		/**< Type of this object. */
  } git_rawobj;
  
  /* EXPORT */
  struct git_odb_object {
  	git_cached_obj cached;
  	git_rawobj raw;
  };
  
  /* EXPORT */
  struct git_odb {
  	git_refcount rc;
  	git_vector backends;
  	git_cache cache;
  };
  
  /*
   * Hash a git_rawobj internally.
   * The `git_rawobj` is supposed to be previously initialized
   */
  int git_odb__hashobj(git_oid *id, git_rawobj *obj);
  
  /*
   * Hash an open file descriptor.
   * This is a performance call when the contents of a fd need to be hashed,
   * but the fd is already open and we have the size of the contents.
   *
   * Saves us some `stat` calls.
   *
   * The fd is never closed, not even on error. It must be opened and closed
   * by the caller
   */
  int git_odb__hashfd(git_oid *out, git_file fd, size_t size, git_otype type);
  
  /*
   * Hash an open file descriptor applying an array of filters
   * Acts just like git_odb__hashfd with the addition of filters...
   */
  int git_odb__hashfd_filtered(
  	git_oid *out, git_file fd, size_t len, git_otype type, git_vector *filters);
  
  /*
   * Hash a `path`, assuming it could be a POSIX symlink: if the path is a
   * symlink, then the raw contents of the symlink will be hashed. Otherwise,
   * this will fallback to `git_odb__hashfd`.
   *
   * The hash type for this call is always `GIT_OBJ_BLOB` because symlinks may
   * only point to blobs.
   */
  int git_odb__hashlink(git_oid *out, const char *path);
  
  /*
   * Generate a GIT_ENOTFOUND error for the ODB.
   */
  int git_odb__error_notfound(const char *message, const git_oid *oid);
  
  /*
   * Generate a GIT_EAMBIGUOUS error for the ODB.
   */
  int git_odb__error_ambiguous(const char *message);
  
  /*
   * Attempt to read object header or just return whole object if it could
   * not be read.
   */
  int git_odb__read_header_or_object(
  	git_odb_object **out, size_t *len_p, git_otype *type_p,
  	git_odb *db, const git_oid *id);
  
  #endif
  

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