145 lines
4.1 KiB
Python
145 lines
4.1 KiB
Python
# Copyright 2016 Virgil Dupras
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#
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# This software is licensed under the "GPLv3" License as described in the "LICENSE" file,
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# which should be included with this package. The terms are also available at
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# http://www.gnu.org/licenses/gpl-3.0.html
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import os
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import os.path as op
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import shelve
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import tempfile
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from collections import namedtuple
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from .cache import string_to_colors, colors_to_string
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def wrap_path(path):
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return "path:{}".format(path)
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def unwrap_path(key):
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return key[5:]
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def wrap_id(path):
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return "id:{}".format(path)
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def unwrap_id(key):
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return int(key[3:])
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CacheRow = namedtuple("CacheRow", "id path blocks mtime")
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class ShelveCache:
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"""A class to cache picture blocks in a shelve backend.
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"""
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def __init__(self, db=None, readonly=False):
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self.istmp = db is None
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if self.istmp:
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self.dtmp = tempfile.mkdtemp()
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self.ftmp = db = op.join(self.dtmp, "tmpdb")
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flag = "r" if readonly else "c"
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self.shelve = shelve.open(db, flag)
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self.maxid = self._compute_maxid()
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def __contains__(self, key):
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return wrap_path(key) in self.shelve
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def __delitem__(self, key):
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row = self.shelve[wrap_path(key)]
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del self.shelve[wrap_path(key)]
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del self.shelve[wrap_id(row.id)]
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def __getitem__(self, key):
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if isinstance(key, int):
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skey = self.shelve[wrap_id(key)]
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else:
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skey = wrap_path(key)
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return string_to_colors(self.shelve[skey].blocks)
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def __iter__(self):
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return (unwrap_path(k) for k in self.shelve if k.startswith("path:"))
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def __len__(self):
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return sum(1 for k in self.shelve if k.startswith("path:"))
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def __setitem__(self, path_str, blocks):
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blocks = colors_to_string(blocks)
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if op.exists(path_str):
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mtime = int(os.stat(path_str).st_mtime)
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else:
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mtime = 0
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if path_str in self:
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rowid = self.shelve[wrap_path(path_str)].id
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else:
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rowid = self._get_new_id()
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row = CacheRow(rowid, path_str, blocks, mtime)
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self.shelve[wrap_path(path_str)] = row
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self.shelve[wrap_id(rowid)] = wrap_path(path_str)
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def _compute_maxid(self):
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return max(
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(unwrap_id(k) for k in self.shelve if k.startswith("id:")), default=1
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)
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def _get_new_id(self):
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self.maxid += 1
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return self.maxid
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def clear(self):
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self.shelve.clear()
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def close(self):
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if self.shelve is not None:
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self.shelve.close()
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if self.istmp:
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os.remove(self.ftmp)
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os.rmdir(self.dtmp)
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self.shelve = None
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def filter(self, func):
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to_delete = [key for key in self if not func(key)]
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for key in to_delete:
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del self[key]
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def get_id(self, path):
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if path in self:
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return self.shelve[wrap_path(path)].id
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else:
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raise ValueError(path)
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def get_multiple(self, rowids):
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for rowid in rowids:
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try:
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skey = self.shelve[wrap_id(rowid)]
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except KeyError:
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continue
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yield (rowid, string_to_colors(self.shelve[skey].blocks))
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def purge_outdated(self):
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"""Go through the cache and purge outdated records.
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A record is outdated if the picture doesn't exist or if its mtime is greater than the one in
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the db.
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"""
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todelete = []
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for path in self:
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row = self.shelve[wrap_path(path)]
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if row.mtime and op.exists(path):
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picture_mtime = os.stat(path).st_mtime
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if int(picture_mtime) <= row.mtime:
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# not outdated
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continue
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todelete.append(path)
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for path in todelete:
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try:
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del self[path]
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except KeyError:
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# I have no idea why a KeyError sometimes happen, but it does, as we can see in
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# #402 and #439. I don't think it hurts to silently ignore the error, so that's
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# what we do
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pass
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