From 6b0eda14a11ba243e7adf3900aae75ba23980c96 Mon Sep 17 00:00:00 2001
From: ThibG <thib@sitedethib.com>
Date: Sat, 16 Mar 2019 20:18:47 +0100
Subject: [PATCH] Avoid race condition when streaming deleted statuses (#10280)

* Avoid race condition when streaming deleted statuses

* Move redis lock to DistributionWorker to avoid extra Redis value
---
 app/services/remove_status_service.rb | 30 ++++++++++++++++++---------
 app/workers/distribution_worker.rb    |  8 ++++++-
 2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/app/services/remove_status_service.rb b/app/services/remove_status_service.rb
index 98875429d1..747f209f33 100644
--- a/app/services/remove_status_service.rb
+++ b/app/services/remove_status_service.rb
@@ -14,16 +14,22 @@ class RemoveStatusService < BaseService
     @stream_entry = status.stream_entry
     @options      = options
 
-    remove_from_self if status.account.local?
-    remove_from_followers
-    remove_from_lists
-    remove_from_affected
-    remove_reblogs
-    remove_from_hashtags
-    remove_from_public
-    remove_from_media if status.media_attachments.any?
-
-    @status.destroy!
+    RedisLock.acquire(lock_options) do |lock|
+      if lock.acquired?
+        remove_from_self if status.account.local?
+        remove_from_followers
+        remove_from_lists
+        remove_from_affected
+        remove_reblogs
+        remove_from_hashtags
+        remove_from_public
+        remove_from_media if status.media_attachments.any?
+
+        @status.destroy!
+      else
+        raise Mastodon::RaceConditionError
+      end
+    end
 
     # There is no reason to send out Undo activities when the
     # cause is that the original object has been removed, since
@@ -156,4 +162,8 @@ class RemoveStatusService < BaseService
     redis.publish('timeline:public:media', @payload)
     redis.publish('timeline:public:local:media', @payload) if @status.local?
   end
+
+  def lock_options
+    { redis: Redis.current, key: "distribute:#{@status.id}" }
+  end
 end
diff --git a/app/workers/distribution_worker.rb b/app/workers/distribution_worker.rb
index f423d43ae5..4e20ef31bf 100644
--- a/app/workers/distribution_worker.rb
+++ b/app/workers/distribution_worker.rb
@@ -4,7 +4,13 @@ class DistributionWorker
   include Sidekiq::Worker
 
   def perform(status_id)
-    FanOutOnWriteService.new.call(Status.find(status_id))
+    RedisLock.acquire(redis: Redis.current, key: "distribute:#{status_id}") do |lock|
+      if lock.acquired?
+        FanOutOnWriteService.new.call(Status.find(status_id))
+      else
+        raise Mastodon::RaceConditionError
+      end
+    end
   rescue ActiveRecord::RecordNotFound
     true
   end