TODO 2.2

- alternative backend based on libevent ?
better performance than current select() backend under high load, should be
implemented as a build-time option

- explore usage of SPL fixed arrays and queues
better overall cpu and memory usage than native PHP hash table based arrays

- support for accept mutex (sysv sem/shm ?)
avoid the thundering herd effect with kernels that wake up all listening
processes when there's an incoming connection with a hybrid prefork+multiplex
process model