Perl UV binding hits version 2.000

Over the past few months I've been working on finishing off the libuv Perl binding module, UV. Yesterday I finally got it finished enough to feel like calling it version 2.000. Now's a good time to take a look at it.

libuv itself is a cross-platform event handling library, which focuses on providing nicely portable abstractions for things like TCP sockets, timers, and sub-process management between UNIX, Windows and other platforms. Traditionally things like event-based socket handling have always been difficult to write in a portable way between Windows and other places due to the very different ways things work on Windows as opposed to anywhere else. libuv provides a large number of helpful wrappers to write event-based code in a portable way, freeing the developer from having to care about these things.

A number of languages have nice bindings for libuv, but until recently there wasn't a good one for Perl. My latest project for The Perl Foundation aimed to fix this. The latest release of UV version 2.000 indicates that this is now done.

It's unlikely that most programs would choose to operate directly with UV itself, but rather via some higher-level event system. There are UV adapter modules for IO::Async (IO::Async::Loop::UV), Mojo (Mojo::Reactor::UV), and Future::IO (Future::IO::Impl::UV) at least.

The UV module certainly wraps much of what libuv has to offer, but there are still some parts missing. libuv can watch filesystems for changes of files, and provides asynchronous filesystem access access functions - both of these are currently missing from the Perl binding. Threadpools are an entire concept that doesn't map very well to the Perl language, so they are absent too. Finally, libuv lists an entire category of "miscellaneous functions", most of which are already available independently in Perl, so there seems little point to wrapping those provided by libuv.

Finally, we should take note of one thing that doesn't work - the UV::TCP->open and UV::UDP->open functions when running on Windows. The upshot here is that you cannot create TCP or UDP sockets in your application independently of libuv and then hand them over to be handled by the library; this is not permitted. This is because on Windows, there are fundamentally two different kinds of sockets that require two different sets of API to access them - ones using WSA_FLAG_OVERLAPPED, and ones not. libuv needs that flag in order to perform event-based IO on sockets, and so it won't work with sockets created without it - which is the usual kind that most other modules, and perl itself, will create. This means that on Windows, the only sockets you can use with the UV module are ones created by UV itself - such as by asking it to connect out to servers, or listen and accept incoming connections. Fortunately, this is sufficient for the vast majority of applications.

I would like to finish up by saying thanks to The Perl Foundation for funding me to complete this project.

Source: leonerds code

Perl UV binding hits version 2.000