diff options
Diffstat (limited to 'Lib/dumbdbm.py')
| -rw-r--r-- | Lib/dumbdbm.py | 97 |
1 files changed, 69 insertions, 28 deletions
diff --git a/Lib/dumbdbm.py b/Lib/dumbdbm.py index b932f84..1af22b1 100644 --- a/Lib/dumbdbm.py +++ b/Lib/dumbdbm.py @@ -33,11 +33,26 @@ error = IOError # For anydbm class _Database(UserDict.DictMixin): - def __init__(self, file, mode): + def __init__(self, filebasename, mode): self._mode = mode - self._dirfile = file + _os.extsep + 'dir' - self._datfile = file + _os.extsep + 'dat' - self._bakfile = file + _os.extsep + 'bak' + + # The directory file is a text file. Each line looks like + # "%r, (%d, %d)\n" % (key, pos, siz) + # where key is the string key, pos is the offset into the dat + # file of the associated value's first byte, and siz is the number + # of bytes in the associated value. + self._dirfile = filebasename + _os.extsep + 'dir' + + # The data file is a binary file pointed into by the directory + # file, and holds the values associated with keys. Each value + # begins at a _BLOCKSIZE-aligned byte offset, and is a raw + # binary 8-bit string value. + self._datfile = filebasename + _os.extsep + 'dat' + self._bakfile = filebasename + _os.extsep + 'bak' + + # The index is an in-memory dict, mirroring the directory file. + self._index = None # maps keys to (pos, siz) pairs + # Mod by Jack: create data file if needed try: f = _open(self._datfile, 'r') @@ -46,6 +61,7 @@ class _Database(UserDict.DictMixin): f.close() self._update() + # Read directory file into the in-memory index dict. def _update(self): self._index = {} try: @@ -53,21 +69,28 @@ class _Database(UserDict.DictMixin): except IOError: pass else: - while 1: - line = f.readline().rstrip() - if not line: break - key, (pos, siz) = eval(line) - self._index[key] = (pos, siz) + for line in f: + key, pos_and_siz_pair = eval(line) + self._index[key] = pos_and_siz_pair f.close() + # Write the index dict to the directory file. The original directory + # file (if any) is renamed with a .bak extension first. If a .bak + # file currently exists, it's deleted. def _commit(self): - try: _os.unlink(self._bakfile) - except _os.error: pass - try: _os.rename(self._dirfile, self._bakfile) - except _os.error: pass + try: + _os.unlink(self._bakfile) + except _os.error: + pass + + try: + _os.rename(self._dirfile, self._bakfile) + except _os.error: + pass + f = _open(self._dirfile, 'w', self._mode) for key, (pos, siz) in self._index.items(): - f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`)) + f.write("%r, (%d, %d)\n" % (key, pos, siz)) f.close() def __getitem__(self, key): @@ -78,21 +101,25 @@ class _Database(UserDict.DictMixin): f.close() return dat + # Append val to the data file, starting at a _BLOCKSIZE-aligned + # offset. The data file is first padded with NUL bytes (if needed) + # to get to an aligned offset. Return pair + # (starting offset of val, len(val)) def _addval(self, val): f = _open(self._datfile, 'rb+') f.seek(0, 2) pos = int(f.tell()) -## Does not work under MW compiler -## pos = ((pos + _BLOCKSIZE - 1) / _BLOCKSIZE) * _BLOCKSIZE -## f.seek(pos) npos = ((pos + _BLOCKSIZE - 1) // _BLOCKSIZE) * _BLOCKSIZE f.write('\0'*(npos-pos)) pos = npos - f.write(val) f.close() return (pos, len(val)) + # Write val to the data file, starting at offset pos. The caller + # is responsible for ensuring that there's enough room starting at + # pos to hold val, without overwriting some other value. Return + # pair (pos, len(val)). def _setval(self, pos, val): f = _open(self._datfile, 'rb+') f.seek(pos) @@ -100,31 +127,45 @@ class _Database(UserDict.DictMixin): f.close() return (pos, len(val)) - def _addkey(self, key, (pos, siz)): - self._index[key] = (pos, siz) + # key is a new key whose associated value starts in the data file + # at offset pos and with length size. Add an index record to + # the in-memory index dict, and append one to the index file. + def _addkey(self, key, pos_and_siz_pair): + self._index[key] = pos_and_siz_pair f = _open(self._dirfile, 'a', self._mode) - f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`)) + f.write("%r, %r\n" % (key, pos_and_siz_pair)) f.close() def __setitem__(self, key, val): if not type(key) == type('') == type(val): raise TypeError, "keys and values must be strings" - if not key in self._index: - (pos, siz) = self._addval(val) - self._addkey(key, (pos, siz)) + if key not in self._index: + self._addkey(key, self._addval(val)) else: + # See whether the new value is small enough to fit in the + # (padded) space currently occupied by the old value. pos, siz = self._index[key] oldblocks = (siz + _BLOCKSIZE - 1) // _BLOCKSIZE newblocks = (len(val) + _BLOCKSIZE - 1) // _BLOCKSIZE if newblocks <= oldblocks: - pos, siz = self._setval(pos, val) - self._index[key] = pos, siz + self._index[key] = self._setval(pos, val) else: - pos, siz = self._addval(val) - self._index[key] = pos, siz + # The new value doesn't fit in the (padded) space used + # by the old value. The blocks used by the old value are + # forever lost. + self._index[key] = self._addval(val) + + # Note that _index may be out of synch with the directory + # file now: _setval() and _addval() don't update the directory + # file. def __delitem__(self, key): + # The blocks used by the associated value are lost. del self._index[key] + # XXX It's unclear why we do a _commit() here (the code always + # XXX has, so I'm not changing it). _setitem__ doesn't try to + # XXX keep the directory file in synch. Why should we? Or + # XXX why shouldn't __setitem__? self._commit() def keys(self): |