def _refresh(self):
"""Update table of contents mapping."""
# If it has been less than two seconds since the last _refresh() call,
# we have to unconditionally re-read the mailbox just in case it has
# been modified, because os.path.mtime() has a 2 sec resolution in the
# most common worst case (FAT) and a 1 sec resolution typically. This
# results in a few unnecessary re-reads when _refresh() is called
# multiple times in that interval, but once the clock ticks over, we
# will only re-read as needed. Because the filesystem might be being
# served by an independent system with its own clock, we record and
# compare with the mtimes from the filesystem. Because the other
# system's clock might be skewing relative to our clock, we add an
# extra delta to our wait. The default is one tenth second, but is an
# instance variable and so can be adjusted if dealing with a
# particularly skewed or irregular system.
if time.time() - self._last_read > 2 + self._skewfactor:
refresh = False
for subdir in self._toc_mtimes:
mtime = os.path.getmtime(self._paths[subdir])
if mtime > self._toc_mtimes[subdir]:
refresh = True
self._toc_mtimes[subdir] = mtime
if not refresh:
return
# Refresh toc
self._toc = {}
for subdir in self._toc_mtimes:
path = self._paths[subdir]
for entry in os.listdir(path):
p = os.path.join(path, entry)
if os.path.isdir(p):
continue
uniq = entry.split(self.colon)[0]
self._toc[uniq] = os.path.join(subdir, entry)
self._last_read = time.time()
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