Krzysztof Nowicki authored Aug 04, 2020 and Laurent Montel committed Aug 24, 2021

When collections were synchronized through the resource scheduler they
were naturally serialized by the queues implemented there. Enabling
direct collection synchronization in response to server notifications
introduced a problem - the synchronizations were not serialized in any
way and could execute in parallel. It could even happen, tha the same
collection was synchronized by two parallel requests, which would
result in double items appearing in the message list.

Solve this problem by introducing an internal collection
synchronization queue.