File size: 2,149 Bytes
63a63dd | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 | import json
from collections import OrderedDict
from queue import Queue
class CachedQueue(Queue):
"""Queue with cache
This queue is used in :class:`ThreadPool`, it enables parser and downloader
to check if the page url or the task has been seen or processed before.
Attributes:
_cache (OrderedDict): cache, elements are stored as keys of it.
cache_capacity (int): maximum size of cache.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if "cache_capacity" in kwargs:
self.cache_capacity = kwargs["cache_capacity"]
else:
self.cache_capacity = 0
self._cache = OrderedDict()
def is_duplicated(self, item):
"""Check whether the item has been in the cache
If the item has not been seen before, then hash it and put it into
the cache, otherwise indicates the item is duplicated. When the cache
size exceeds capacity, discard the earliest items in the cache.
Args:
item (object): The item to be checked and stored in cache. It must
be immutable or a list/dict.
Returns:
bool: Whether the item has been in cache.
"""
if isinstance(item, dict):
hashable_item = json.dumps(item, sort_keys=True)
elif isinstance(item, list):
hashable_item = frozenset(item)
else:
hashable_item = item
if hashable_item in self._cache:
return True
else:
if self.cache_capacity > 0 and len(self._cache) >= self.cache_capacity:
self._cache.popitem(False)
self._cache[hashable_item] = 1
return False
def put(self, item, block=True, timeout=None, dup_callback=None):
"""Put an item to queue if it is not duplicated."""
if not self.is_duplicated(item):
super().put(item, block, timeout)
else:
if dup_callback:
dup_callback(item)
def put_nowait(self, item, dup_callback=None):
self.put(item, block=False, dup_callback=dup_callback)
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