Skip to main content

Asyncronous Database Records

Through persistance systems, notably Divmod's Axiom project, i have been experimenting with the idea of asyncronous request of items which may or may not exist for some time. The idea is an abstraction of a terrible first idea for "persistant deferreds," which my very suggestion of lead to horrible responses over in #twisted, but well deserved, I now believe.

The concept is similar but perhaps simplified for the limitations and complications involved. Operations may return an "asyncronous item," which in my implementation is done by an Item implementing the IAsyncronousOperation ("operation" may be replaced with "Item") interface. This is akin to returning a deferred. The item allows the caller to control the response to the availability of the item, but in a way that can survive server crashes and reboots, and is otherwise a persistant record, and not an emphemeral object.

Borrowing additionally from Twisted, the asyncronous results can support both positive and negative handlers, set for managing the result as success or error. The creation of these handlers constitutes an additional asyncronous result, which can be used to chain handlers, akin to the callback chains of Twisted. In the event that the requested item is ready, which is either immediately or in the future, the appropriate handler is called and the asyncronous result handlers are cleaned up.

I will release the code soon, when the rest of the unittests are complete and an example usecase can demonstrate the usefulness. I have gotten some negative reaction from this one, and I really hope it can be attributed to misconceptions of my intent and failure to consider the right usecases. Hopefully I can remedy this.

Comments

mrshoe said…
Shouldn't everything persist through server crashes, power outages, and restarts? Check out http://www.capros.org/.
Josiah Carlson said…
That sounds a bit like a trigger plus a stored procedure in a database with callback registration. But maybe I'm over-thinking it.

Popular posts from this blog

Respect and Code Reviews

Code Reviews in a development team only function best, or possible at all, when everyone approaches them with respect. That’s something I’ve usually taken for granted because I’ve had the opportunity to work with amazing developers who shine not just in their technical skills but in their interpersonal skills on a team. That isn’t always the case, so I’m going to put into words something that often exists just in assumptions.
You have to respect your code. This is first only because the nature and intent of code reviews are to safeguard the quality of your code, so even having code reviews demonstrates a baseline of respect for that code. But, maybe not everyone on the team has the same level of respect or entered a team with existing review traditions that they aren’t acquainted with.
There can be culture shock when you enter a team that’s really heavy on code reviews, but also if you enter a team or interact with a colleague who doesn’t share that level of respect for the process or…

CARDIAC: The Cardboard Computer

I am just so excited about this.


CARDIAC. The Cardboard Computer. How cool is that? This piece of history is amazing and better than that: it is extremely accessible. This fantastic design was built in 1969 by David Hagelbarger at Bell Labs to explain what computers were to those who would otherwise have no exposure to them. Miraculously, the CARDIAC (CARDboard Interactive Aid to Computation) was able to actually function as a slow and rudimentary computer. 
One of the most fascinating aspects of this gem is that at the time of its publication the scope it was able to demonstrate was actually useful in explaining what a computer was. Could you imagine trying to explain computers today with anything close to the CARDIAC?

It had 100 memory locations and only ten instructions. The memory held signed 3-digit numbers (-999 through 999) and instructions could be encoded such that the first digit was the instruction and the second two digits were the address of memory to operate on. The only re…

How To Care If BSD, MIT, or GPL Licenses Are Used

The two recent posts about some individuals' choice of GPL versus others' preference for BSD and MIT style licensing has caused a lot of debate and response. I've seen everything as an interesting combination of very important topics being taken far too seriously and far too personally. All involved need to take a few steps back.

For the uninitiated and as a clarifier for the initiated, we're dealing with (basically) three categories of licensing when someone releases software (and/or its code):
Closed Source. Easiest to explain, because you just get nothing.GPL. If you get the software, you get the source code, you get to change it, and anything you combine it with must be under the same terms.MIT and BSD. If you get the software, you might get the source code, you get to change it, and you have no obligations about anything else you combine it with.The situation gets stickier when we look at those combinations and the transitions between them.

Use GPL code with Closed S…