Lib/statcache.py

   1 """Maintain a cache of stat() information on files.
   2
   3 There are functions to reset the cache or to selectively remove items.
   4 """
   5
   6 import os as _os
   7 from stat import *
   8
   9 __all__ = ["stat","reset","forget","forget_prefix","forget_dir",
  10            "forget_except_prefix","isdir"]
  11
  12 # The cache.  Keys are pathnames, values are os.stat outcomes.
  13 # Remember that multiple threads may be calling this!  So, e.g., that
  14 # cache.has_key(path) returns 1 doesn't mean the cache will still contain
  15 # path on the next line.  Code defensively.
  16
  17 cache = {}
  18
  19 def stat(path):
  20     """Stat a file, possibly out of the cache."""
  21     ret = cache.get(path, None)
  22     if ret is None:
  23         cache[path] = ret = _os.stat(path)
  24     return ret
  25
  26 def reset():
  27     """Clear the cache."""
  28     cache.clear()
  29
  30 # For thread saftey, always use forget() internally too.
  31 def forget(path):
  32     """Remove a given item from the cache, if it exists."""
  33     try:
  34         del cache[path]
  35     except KeyError:
  36         pass
  37
  38 def forget_prefix(prefix):
  39     """Remove all pathnames with a given prefix."""
  40     for path in cache.keys():
  41         if path.startswith(prefix):
  42             forget(path)
  43
  44 def forget_dir(prefix):
  45     """Forget a directory and all entries except for entries in subdirs."""
  46
  47     # Remove trailing separator, if any.  This is tricky to do in a
  48     # x-platform way.  For example, Windows accepts both / and \ as
  49     # separators, and if there's nothing *but* a separator we want to
  50     # preserve that this is the root.  Only os.path has the platform
  51     # knowledge we need.
  52     from os.path import split, join
  53     prefix = split(join(prefix, "xxx"))[0]
  54     forget(prefix)
  55     for path in cache.keys():
  56         # First check that the path at least starts with the prefix, so
  57         # that when it doesn't we can avoid paying for split().
  58         if path.startswith(prefix) and split(path)[0] == prefix:
  59             forget(path)
  60
  61 def forget_except_prefix(prefix):
  62     """Remove all pathnames except with a given prefix.
  63
  64     Normally used with prefix = '/' after a chdir().
  65     """
  66
  67     for path in cache.keys():
  68         if not path.startswith(prefix):
  69             forget(path)
  70
  71 def isdir(path):
  72     """Return 1 if directory, else 0."""
  73     try:
  74         st = stat(path)
  75     except _os.error:
  76         return 0
  77     return S_ISDIR(st[ST_MODE])