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FIX: Prevent deadlock (#7691)

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Before the locking here was added, replying to a post and liking a post
at roughly the same time could cause a deadlock.

Liking a post grabs an update lock on the post and then on the topic (to
update like counts).

We now lock the replied to post before getting the topic lock so that we
can update the replied to post later without causing a deadlock.
This commit is contained in:
Daniel Waterworth 2019-06-05 01:29:27 +00:00 committed by Sam
parent 9779307efc
commit 3407445831
1 changed files with 10 additions and 0 deletions
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10
lib/post_creator.rb
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@ -272,8 +272,18 @@ class PostCreator
def self.set_reply_info(post)
return unless post.reply_to_post_number.present?
# Before the locking here was added, replying to a post and liking a post
# at roughly the same time could cause a deadlock.
#
# Liking a post grabs an update lock on the post and then on the topic (to
# update like counts).
#
# Here, we lock the replied to post before getting the topic lock so that
# we can update the replied to post later without causing a deadlock.
reply_info = Post.where(topic_id: post.topic_id, post_number: post.reply_to_post_number)
.select(:user_id, :post_type)
.lock
.first
if reply_info.present?