rare System.IndexOutOfRangeException when reusing EncodedConnection object

[shimr12]

Hi.
I use a very small pool of EncodedConnections and share them between threads.
I saw here a mention that EncodedConnection is thread safe so my usage is normal.

I rarely get a System.IndexOutOfRangeException when trying to call EncodedConnection.SubscribeAsync.

example stacktrace:

System.IndexOutOfRangeException: Index was outside the bounds of the array.\n   
at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)\n   
at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)\n   
at NATS.Client.EncodedConnection.subscribeAsync(String subject, String reply, EventHandler`1 handler)\n   
at NATS.Client.EncodedConnection.SubscribeAsync(String subject, String queue, EventHandler`1 handler)\n   

calling Dictionary.Add shouldn't raise System.IndexOutOfRangeException normally.
usually it means your using it from multiple threads without locking.

I took a glance at the code here and it confirms it.

if EncodedConnection supposed to be thread-safe this is a bug.

[hastarin]

Perhaps a ConcurrentDictionary should be used instead.
https://docs.microsoft.com/en-us/dotnet/api/system.collections.concurrent.concurrentdictionary-2?view=netframework-4.6.2