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What are the main differences between select, epoll, kqueue and evport?

I recently read Redis. Redis implements a simple event driven library based on I / O multiplexing. Redis says it would pick the best multiplexing supported by the system and gives the following code:

/* Include the best multiplexing layer supported by this system.
 * The following should be ordered by performances, descending. */
#ifdef HAVE_EVPORT
#include "ae_evport.c"
#else
    #ifdef HAVE_EPOLL
    #include "ae_epoll.c"
    #else
        #ifdef HAVE_KQUEUE
        #include "ae_kqueue.c"
        #else
        #include "ae_select.c"
        #endif
    #endif
#endif

I want to know if they have fundamental performance differences? If so, why?

Regards

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In general, all Async I / O subsystems have different internal components, but in the current particular case, these particular asynchronous I / O libraries are used to support as many platforms as possible. I.e:

  • evport = Solaris 10
  • epoll = Linux
  • kqueue = OS X, FreeBSD
  • select = is usually set on all platforms asfallback



Evport

, Epoll

and KQueue

have an O (1) complexity of the descriptor selection algorithm , and they all use the internal memory structures of the kernel space. Also, they can serve lots (hundreds of thousands) file descriptors .

Apart from the rest, it select

can only serve descriptors up to 1024 and does a full scan of the descriptors (so every time it iterates through all the descriptors to pick one to work with), so the complexity is O (n) .

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