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Eclipse/BSD employs SRP (Signaled Receiver Processing) [7] for network input processing. SRP demultiplexes incoming packets before network and higher-level protocol processing. Unlike FreeBSD's single IP input queue and input protocol processing at software interrupt level, SRP uses an unprocessed input queue (UIQ) per socket and processes input protocols in the context of the respective applications. If a socket's queue is full, SRP drops new packets for that socket immediately, unlike FreeBSD, which wastefully processes packets that will need to be dropped. Because SRP processes protocols in the context of the respective receiving applications, SRP can avoid receive livelock [16], a network input overload condition that prevents any packets from being processed by an application.

When SRP enqueues a packet into a socket's UIQ, SRP signals SIGUIQ to the applications that own that socket. The default action for SIGUIQ is to perform input protocol processing (asynchronously to the applications). However, applications can synchronize such processing by catching SIGUIQ and deferring protocol processing until a later input call (e.g., recv). Synchronous protocol processing may improve cache locality. Unlike LRP (Lazy Receive Processing) [10], SRP does not use separate kernel threads for asynchronous protocol processing (kernel threads are not available in FreeBSD).

Jose Brustoloni