Couldn't agree more. Also with SwiftNIO Transport Services, SwiftNIO can actually run on top of Network.framework. In this case you'll use a different EventLoop type (NIOTSEventLoopGroup instead of MultiThreadedEventLoopGroup for NIO on BSD sockets) which executes on DispatchGroups. NIOTSEventLoopGroup gives you all the same synchronisation guarantees as MultiThreadedEventLoopGroup but the underlying thread may change (as DispatchGroups aren't bound to a thread). Long story short: Even considering only SwiftNIO you cannot universally assume that thread locals always work.
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