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_posts/2013-04-07-async-with-ada.md

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+---
+layout: post
+title: Async sockets in Ada
+tags:
+- programming
+- ada
+- epoll
+- async
+---
+
+Recently I've been experimenting with the concept of a high-performance (high
+parallelism, high concurrency, low CPU/memory footprint) TCP server in Ada. Developing on
+top of Linux, you cannot help avoid the
+[epoll(7)](https://en.wikipedia.org/wiki/epoll) I/O event notification
+system.
+
+
+Unlike my previous post [on dynamic task creation in
+Ada](/2013/03/09/dynamic-tasks-in-ada.html), this post won't have much in the
+way of sample code and walk-through. Mostly because I didn't want to spend the
+entire post explaining `epoll(7)` concepts.
+
+If you're currently unfamiliar with
+epoll, I found [this post from
+banu.com](https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/)
+interesting and useful. In general, I think that it is very useful to
+understand how both `epoll(7)` and its BSD-friendly pal `kqueue(2)` work, and
+how the two have influenced evented I/O systems that have become popular in the
+past few years.
+
+
+For my experiment, the primary challenge with using `epoll(7)` is wrapping the
+C code with Ada, which on its face this isn't terribly difficult. That said,
+mapping C arrays and other stupid pointer tricks that C libraries are prone to
+using, can make writing an Ada binding much more difficult. I don't
+intend to dive too deep into how one can create such a binding since I think
+Felix Krause's post on [writing thin/thick C bindings in
+Ada](http://flyx.org/2012/06/13/adabindings1/) is a pretty good introduction on
+that subject. Personally I prefer "thicker" bindings for use in Ada, just as I
+expect Ruby libraries to abstract away the more fickle aspects of the
+underlying C API.
+
+
+
+What I *did* want to share in this post was the actual **working** results of
+my tinkering, which can be found [here, on GitHub](https://github.com/rtyler/ada-playground/tree/master/epollecho).
+
+
+The basic flow of the program (found in `main.adb`) is similar to the example
+found in the `epoll(7)` man page, in that it sets up the `epollfd`, binds the
+listening to it and then waits for `Epoll.Wait` to return with an array of
+socket descriptors which have activity on them.
+
+My next step is to combine this [basic epoll
+binding](https://github.com/rtyler/ada-playground/blob/master/epollecho/src/epoll.ads)
+with my [previous task related
+code](/2013/03/09/dynamic-tasks-in-ada.html) and create a TCP server which uses
+a task pool to perform "work" on the incoming sockets given to it by an
+epoll-listener task.