def __init__(self, cache_dir, log=None, skip_cache=False):
# TODO: instead of storing N artifact packages, store M megabytes.
CacheManager.__init__(self, cache_dir, 'fetch', MAX_CACHED_ARTIFACTS, cache_callback=self.delete_file, log=log, skip_cache=skip_cache)
self._cache_dir = cache_dir
size_limit = 1024 * 1024 * 1024 # 1Gb in bytes.
file_limit = 4 # But always keep at least 4 old artifacts around.
persist_limit = PersistLimit(size_limit, file_limit)
self._download_manager = DownloadManager(self._cache_dir, persist_limit=persist_limit)
self._last_dl_update = -1
