Thursday, July 22, 2010

The question nobody is asking

Shirley Sherrod is feeling a little vindictive. That's not surprising. She's been on quite a roller-coaster lately. She wants to sue Andrew Breitbart for releasing that out-of-context videotape of her. Again, that's understandable, although he didn't make the tape, and didn't know it was out-of-context.

She says, "[H]e came at me. He didn’t go after the NAACP; he came at me." Now that's not true. He released the tape in response to the NAACP's accusations of racism among the Tea Party ranks, to show that the NAACP has their own problem with racism. And it did. Sherrod doesn't know it, but she wasn't being held up as a racist, she was the one pointing out that the NAACP has a problem with racists in their ranks. She was Breitbart's ally in this.

The fact that the tape was edited to make her sound more racist than she is, is just a little bit of delicious payback in kind. It doesn't change the real point being made, which is the answer to the question no one is asking: Why was she giving this talk?

Well, she was trying to promote enlightened views on race, of course. (I should probably put "enlightened" in quotes, since her message was that it's "not so much" about black vs. white, but about class warfare instead.) It's admirable to want to promote enlightened views about race reconciliation. To whom would you want to promote such views? To those who already have them? Or to those who seem to identify more with the bad example? I don't think NAACP meetings are like AA meetings, where you get up and talk about how bad you were and everybody sympathizes because they're all recovering racists, too, and that support helps keep you on the wagon.

I think Shirley gave that talk because she believes that the NAACP has a problem with racism in their midst, and she would like to see it improve. Much like Andrew Breitbart.

Friday, July 2, 2010

Javascript and Dojo

Since I don't have any theater projects coming up, I figured I might as well fill in the space with what I'm doing at work. My latest gig is working with Javascript and (in particular) the Dojo toolkit to develop some web apps.

In the process of coming up to speed on Javascript and Dojo (neither of which I have used a great deal), I'm hitting Google a lot to learn how the various things work. There is, of course, some level of documentation on everything at the Dojo site, but in some cases it's incomplete, and I have to look elsewhere for someone to explain it better. So in the hopes that maybe someone else will be doing the same sort of thing someday, I'm offering this post to explain how dojo.deferreds work.
Update: Naturally, an updated version of Dojo has made this whole discussion nearly obsolete. The new features in the deferred are more intuitive.

What is a dojo.deferred?

In short, a dojo.deferred is an alternative to threads, a way of having relatively independent parts of your program running at that same time. As the documentation page says, "threads are hard."

Think of it as a chain of functions, which you build up one link at a time. You schedule them in the deferred, and kick it off, and it will work its way through them while the rest of your program continues to run uninterrupted (particularly useful if it's a time-consuming operating like waiting for a response from some remote server). If it reaches the end of its chain, it will sit and wait until you put another link on it.

Each link in the chain is a pair of functions. Which of them is called depends on what the previous link returned: if it returned an error, the errback function of will be called; if it returned a normal value, the callback function will be called. So it is critical that each function return something.

Building the chain

There are four possible functions you can call to add a link to the chain: addCallback, addErrback, addBoth, and addCallbacks, and which you call depends on whether you want to specify just a callback, just an errback, the same function to be run in either case, or separate functions for each. In general, the first link in the chain can be just a callback, because there's no danger of an error preceding it. But subsequent links should include both; if a piece unexepectedly ends in error and you have no errback to handle it, the whole deferred silently grinds to a halt.

Kicking it off

It might not be obvious that you have to actually start the chain processing. It doesn't start chugging immediately, you have to "prime the pump" with something for it to consider as the return value of the previous link. You do this by calling its callback() method, which you pass whatever value you want sent to your first callback.

Example time

I find that most examples are too detailed, so I'm going to keep this one more abstract, so that you see what the deferred is all about and don't get lost in the weeds.

//Let's say we have some functions we're going to chain up
* The deferred is going to call each with the
* result returned by the previous one

function thing_one(i) {
return 'Done with 1';
function thing_two(result) {
return 'Done with 2';
function thing_three(result) {
return 'Done with 3';

/* And here's a generic error function to
* use for every step
function myErrback(e) {
alert("Some step of the deferred returned an error!");

// Create the deferred
my d = new dojo.Deferred();
// Chain up the steps
// No chance of failure, so no errback on the first
d.addCallbacks(thing_two, myErrback);
d.addCallbacks(thing_three, myErrback);
// Kick it off by passing 'Go!' to thing_one

Note that even after you kick it off, you can add more function pairs to the chain, and they will be processed in the order received. I hope this helps somebody understand this nifty tool.