25 May 2011 dan   » (Master)

Give me back my event loop

My new phone has now been emancipated, thanks in part to Atheer-pronounced-Arthur (or possibly vice versa) at the “Root” internet cafe on Edgware Road. They have an XTC Clip and he was able to do the S-OFF thing for me in about ten minutes and for the princely sum of £10. Recommended. I have been looking at AOSP build instructions, but actually doing the build and flashing the phone with a nice clean 2.3.4 Sense-free system will have to wait until I can devote a few more mental cycles to it.

In between the distractions of Shiny! New! Toy! I have been working on the projectr/thin-prefork pair – I am still reasonably convinced that they should be independent modules, though as I always seem to end up hacking on both at once I worry about the degree of coupling between them – to impose some sense on the interface for extending the thin-prefork server. Which I think is 80% there, but this morning I thought it was 100% there until I started trying to use it for real, so that’s a little bit annoying.

Which brings us to the rant/plea for today, as indicated in the title. Hands off my event loop! I’m sure I’ve said already this in other contexts and with regard to other platforms, but: I am not going to devote my process to call Oojimaflip.run! when there are other things it should be doing concurrently with watching for Oojimaflips, and I see no reason either to start a new thread (or process) exclusively for your use when you could have just written a method that says whether there are fresh oojimaflips and another to say what they are.

I am prompted to say this by rb-inotify, which is a (quite nicely written) wrapper around some kernel functionality that communicates via a file descriptor. I’d like a wrapper like this to (1) give me the file descriptor so I can call Kernel.select on it, along with all the other files I’m looking at; (2) give me a method which I will call when select says the fd is ready to read, which will read them and (3) digest them into beautiful Ruby-friendly Event objects. What I’ve got is about two out of three (good odds if you’re Meatloaf): there is a public method #to_io whose return value I can plug into select, there are beautiful Ruby-friendly Event objects, but to get those objects, unless I’m overlooking something (and I don’t mean that to sound passive-aggressive), I have to run one cycle of the rb-inotify event loop: call the #process method which calls my callback once per event, which has to find somewhere to store the events it’s passed, and then check the stored events when control eventually unwinds from #process and returns to me.

I’m actually being a bit harsh here, because the event-parsing code is there in the internals and not hard to grab. In the basement lavatory behind the “beware of the leopard” sign, I find a method called read_events, which if you don’t mind calling undocumented code can be used something like this. The preceding call to select would be better replaced by some code to put the file into non-blocking mode, but that’s a refinement that can wait for another time.

I have opened an issue on github saying something similar, which I expect is far more likely to have a useful effect than posting on this obscure blog. But, yeah, I like ranting.

Syndicated 2011-05-20 13:19:57 from diary at Telent Netowrks

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