In a sequential programming model, code is always executed in the order dictated by the semantics of the programming language. Thus, if one operation blocks for some reason (waiting for a resource, and so forth), the whole execution blocks and can only move forward once that operation has completed. This often leads to poor utilization of resources, because the main thread will be busy waiting on one operation. In GUI apps, this also leads to poor user interactivity, because the main thread, which is responsible for managing the GUI, is busy waiting for something else. This is a major problem in our specific case of network programming, as we often need to wait for data to be available on a socket. In the past, we worked around these issues using multiple threads. In that model, we delegated a costly operation to a background thread...
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