From 9817b4b3b491d1860b0198ec75e20b6f4c2b73ee Mon Sep 17 00:00:00 2001 From: Ethan Dalool Date: Fri, 30 Oct 2020 18:42:23 -0700 Subject: [PATCH] Fix livestream getting stuck on deleted posts. --- hnarchive.py | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/hnarchive.py b/hnarchive.py index c80aa09..df34ffc 100644 --- a/hnarchive.py +++ b/hnarchive.py @@ -134,12 +134,35 @@ def get_latest_id(): def livestream(): bo = backoff.Linear(m=2, b=5, max=60) id = select_latest_id() or 1 + # missed_loops: + # Usually, livestream assumes that `item is None` means the requested item + # id hasn't been published yet. But, if that item is actually just deleted, + # we would be stuck waiting for it forever. missed_loops is used to + # ocassionally check get_latest_id to see if new items are available, so we + # know that the current id is really just deleted. + # Items are released in small batches of < ~10 at a time. It is important + # that the number in `latest > id+XXX` is big enough that we are sure the + # requested item is really dead and not just part of a fresh batch that + # beat our check in a race condition (consider that between the last + # iteration which triggered the check and the call to get_latest_id, the + # item we were waiting for is published in a new batch). I chose 50 because + # catching up with 50 items is not a big deal. + missed_loops = 0 while True: item = get_item(id) if item is None: + log.debug('%s does not exist yet.', id) + missed_loops += 1 + if missed_loops % 5 == 0: + latest = get_latest_id() + if latest > (id+50): + log.debug('Skipping %s because future ids exist.', id) + id += 1 + continue time.sleep(bo.next()) continue id += 1 + missed_loops = 0 bo.rewind(2) yield item