rabbit_feature_flags: Protect concurrent reloads of the registry #10027
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[Why] When a node joins another node, it resets its feature flags registry (the registry is unloaded) and it copies the feature flags states from the remote cluster. Before this patch, there was a small window where a concurrent use of the registry right between these two steps would reload a registry from the default/empty states, which does not reflect the intent. This could happen because another node is running peer discovery and queries the cluster membership of the node joining a cluster. [How] We acquire the registry reload lock around the reset+copy and in `rabbit_ff_registry_wrapper`.
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Why
When a node joins another node, it resets its feature flags registry (the registry is unloaded) and it copies the feature flags states from the remote cluster.
Before this patch, there was a small window where a concurrent use of the registry right between these two steps would reload a registry from the default/empty states, which does not reflect the intent.
This could happen because another node is running peer discovery and queries the cluster membership of the node joining a cluster.
How
We acquire the registry reload lock around the reset+copy and in
rabbit_ff_registry_wrapper.