On Dec 20, 2007 6:16 PM, Michał Pasternak <michal.dtz@gmail.com> wrote:
On Thu, 20 Dec 2007 09:23:43 +0000 "Arnar Birgisson" <arnarbi@gmail.com> wrote:
Hi there,
May I ask why you chose libaio over, for example, libevent?
libevent is to C as Twisted is to Python. Both run on many OS/platforms, but neither give you asynchronous file read/write; read(2) on a file descriptor (not socket) will be always blocking. At least this is what I understood after quick glance at libevent source - all it does in buffer.c:evbuffer_read on non-win32 OS is calling read(2).
I'm pretty sure you are mistaken. As I understood, libevent provides a portable API on top of whatever async I/O mechanisms there are on the underlying system, selecting the best available implementation. For Linux, I believe this it currently uses epoll, kqueue on freebsd, or select() or poll() on older systems.
libaio, instead, gives you async filesystem read/write access. Reading a few hundred megabytes of data won't block Twisted reactor, which is good.
libevent provides file and socket i/o, along with timers. Latest version provides buffered i/o and async dns resolver and http server. Please forgive (and ignore) me if I'm completely missing something :)
Of course it would be cool to have Python libevent bindings - and even cooler it would be to have a portable libevent reactor in C - but would that really remove some of the limitations that Twisted has still to deal with? You'd still have to hack portable AIO implementation into libevent to have async file read/writes then ... :)
Python libevent bindings have existed for a while in pyevent, a pyrex binding module: http://code.google.com/p/pyevent/ Not sure how well it is maintained, but I've seen many references to it so it looks like people are using it. As for a libevent based reactor, there is an old ticket and branch for it here: http://twistedmatrix.com/trac/ticket/1930 http://twistedmatrix.com/trac/browser/branches/libevent-1930-3 Googling for "twisted libevent reactor" gives many interesting results. cheers, Arnar