Re: [Libevent-users] question about poll()

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Wed, Nov 25, 2009 at 02:44:37PM -0500, Patrick Galbraith wrote:
> Hi there all!
> 
> I'm working on trying to port libmemcached to Windows. It is not an easy 
> task! I've just found that libmemcached uses poll() and this is a bit of 
> a road-block! What do you guys do to get cross-platform support? How do 
> you transparently use poll() or other mechanisms to provide the 
> functionality that is required depending on platform?

I'm not sure what exactly you're asking; I'll answer two possible
variants of your question.  If you meant something else, my apologies.

If you mean, "how do Libevent users transparently use poll() or other
mechanisms?" then the answer is "by using Libevent": Libevent knows
about lots of different platform-specific poll()-like things, and
tries to use whichever is fastest among the available options.  You
can probably find examples of how to use Libevent by looking in the
regular memcached source.


If you mean, "how do Libevent users transparently use poll() or other
mechanisms?" then the answer is, "by having a separate implementation
for each backend mechanism, compiling as many as will compile on a
given platform, and selecting whichever one of the compiled ones works
best at runtime."  The responsibility of each backend is basically:
    - Know how to start caring about an fd for reading/writing
    - Know how to stop caring about an fd for reading/writing
    - Know how to wait up to a given number of seconds for fds to be
      ready to read/write, and
For an example of one of the simpler such backends, see select.c in
the Libevent source.  See kqueue.c or epoll.c for an example of what
we do for a fancier backend.

hope this helps,
-- 
Nick
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