| 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) |
|
|
