Fixed metrics gauge callback deadlock #350
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merlimat
requested review from
mattisonchao,
coderzc and
RobertIndie
as code owners
| @@ -138,14 +135,18 @@ func (s *shardsDirector) GetOrCreateLeader(namespace string, shardId int64) (Lea | |||
| return nil, err | |||
| } | |||
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| delete(s.followers, shardId) | |||
| if _, ok := s.followers[shardId]; ok { | |||
| s.followersCounter.Dec() | |||
There was a problem hiding this comment.
Is it better to call this line behind delete?
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I think it should be ok either way. We already checked the key is in the map, and the delete will not return error either.
| @@ -169,14 +170,18 @@ func (s *shardsDirector) GetOrCreateFollower(namespace string, shardId int64) (F | |||
| return nil, err | |||
| } | |||
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| delete(s.leaders, shardId) | |||
| if _, ok := s.leaders[shardId]; ok { | |||
| s.leadersCounter.Dec() | |||
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Is it better to call this line behind delete?
mattisonchao
approved these changes
Jun 12, 2023
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When there is a leader election and a Prometheus metrics collection event is happening there is potential for a deadlock between these 2 go-routines:
Shard director gauge callback
This holds the metrics registry mutex and acquires the read-only mutex on the shards director
Wal closing
This holds the shards director mutex and tries to acquire the metrics registry mutex to unregister a gauge callback.
Modifications
Converted the shards director gauge into an up/down counter so that we don't have to acquire any mutex at the metrics collection time.