EventLoop

Usually multiple Channels share the same EventLoop for processing IO / tasks and so share the same processing NIOThread. For a better understanding of how such an EventLoop works internally the following pseudo code may be helpful:

while eventLoop.isOpen {
    /// Block until there is something to process for 1...n Channels
    let readyChannels = blockUntilIoOrTasksAreReady()
    /// Loop through all the Channels
    for channel in readyChannels {
        /// Process IO and / or tasks for the Channel.
        /// This may include things like:
        ///    - accept new connection
        ///    - connect to a remote host
        ///    - read from socket
        ///    - write to socket
        ///    - tasks that were submitted via EventLoop methods
        /// and others.
        processIoAndTasks(channel)
    }
}

Because an EventLoop may be shared between multiple Channels it’s important to NOT block while processing IO / tasks. This also includes long running computations which will have the same effect as blocking in this case.