Some non-blocking architectures use separate threads for IO and others as worker threads. One problem with this design is extra latency because even though the worker is done with its work, the IO thread is blocked on select/epoll. One simple way to wake up selector under such conditions is to open a pipe per selector thread. The read end is made part of selector fd set and the write end is used by the worker thread to write one byte on the pipe which wakes up the selector. This ensures that whenever new fd needs to be registered with select, it wakes up as soon as possible instead of timing out on read timeout.