And so continues one of the biggest constants in software development: the unerring sense among developers that the level of abstraction they’re current working at is exactly the right one for the task at hand. Anything lower-level is seen as barbaric, and anything higher-level is a bloated, slow waste of resources. This remains true even as the overall level of abstraction across the industry marches ever higher.

First the C guys can’t imagine writing in assembly anymore, but C++’s vtable dispatch is still just too slow to consider. Then the C++ guys look back with chagrin at the bad-old-days of rolling their own half-assed object systems in C, but Java is dismissed as a ridiculous pig. Still later, the Java guys sneer at pointers and manual memory management, but JavaScript is ridiculed as a toy “scripting” language for validating web forms. And on and on.

And in the short term, in the moment, they’re often right. But this arrow points only one way, and that’s in the direction of ever-higher abstraction. To judge how much time remains before the next leap forwards, look at the leading edge of the industry.

–John Siracusa (emphasis mine)

Here’s my two cents on the future of abstraction: systems are clearly getting wider (paralell), not faster; technologies like Grand Central Dispatch help us deal with concurrency today, but longer term, I think a functional programming abstraction is the answer.

AppKit, the GUI framework, is not thread safe. In order for things to work properly, you (almost) always need to update GUI classes from the main thread

–Dave Dribin (slightly edited)

I’ve run into UI + threading problem before, but I’d just never seen this limitation of AppKit spelled out.

Dave’s article explains how to call code on the main thread better then I can.

Avoid distributed computing unless your code is going to be run by a single client with a lot of available hardware. Being able to snarf up CPU cycles from idle hardware sitting around in the user’s house sounds cool but just doesn’t pay off most of the time.

Avoid GPGPU on the Mac until Snow Leopard ships unless you have a really good application for it. OpenCL will make GPGPU a lot more practical and flexible, so trying to shoehorn your computationally expensive code into GLSL or CoreImage today just doesn’t seem worth it.

Using multiple processes is a good idea if the subprograms are already written. … If you’re writing your code from scratch, I don’t recommend it unless you have another good reason to write subprocesses, as it’s difficult and the reward just isn’t there.

For multithreading, concentrate on message passing and operations. Multithreading is never easy, but these help greatly to make it simpler and less error prone.

Good OO design will also help a lot here. It’s vastly easier to multithread an app which has already been decomposed into simple objects with well-defined interfaces and loose coupling between them.

–Mike Ash (emphasis mine, line-breaks added). The article has more detail and is very much worth reading.

One point that this advice really drives home for me is that you need to focus on making good code first, and defer micro-optimizations. If taking the time to clean up some code makes it easier to parallelize, then you are optimizing your code by refactoring it, even if at a micro-level you might be making some of it slower by, say, not caching something that takes O(1) time to compute.

Apple does not sell a Mac that’s not multi-core, and even the iPhone has a CPU and a GPU. There’s no question that optimization means parallelization. And all signs point to computers getting more parallel in the future. Any optimization that hurts parallelization is probably a mistake.

…people are now willing to make trade-offs against performance. For the entire history of the PC industry, computers have been too slow, so trade-offs were made in favor of faster CPUs: higher prices and heavier laptops. But today, for many common tasks, the type of CPU you get when you build a $400 lightweight laptop is fast enough. That’s (a) breakthrough.

–John Gruber

Cynically I also wonder if this is because “more cores” isn’t as compelling as faster. As Hank Williams says,

The problem of multi-core computing is really very simple. As most of us have experienced, every problem *can’t* be solved better or faster with more people. Some problems can be solved faster by adding a few people, but most problems cannot. In truth, most problems can best, or only be solved by one person at a time. And so it is with computing. The vast majority of problems can only be solved by one logic thread at a time. The reason is obvious. For most process-oriented work, step B is based on the results of step A. And step C is based on the results of step B, and so on.

Problem:
When using an NSAlert to display a sheet in a multi-threaded application, unexpected badness can happen.

I was using
beginSheetModalForWindow:modalDelegate:didEndSelector:contextInfo:
To display an NSAlert as a sheet.

But when the sheet appeared, the window it was attached to disappeared and got into some weird broken state where it would appear iff the application was not frontmost.

Fortunately, I remembered having encountered weirdness with NSAlert sheets before. The symptoms were different (previously the alert didn’t have focus), but the same solution still worked.

Solution: make sure the message to display the sheet is sent by the main thread. To do this, put the call to beginSheetModalForWindow:modalDelegate:didEndSelector:contextInfo: inside another method, showMyAlert, then use performSelectorOnMainThread:withObject:waitUntilDone: to make sure showMyAlert is called on the main thread.

Work around use runModal to display the alert as a modal dialog instead of a sheet. runModal Does not appear to have any problems when called from other threads.

Just like last time:

The whole incident feels funny to me. I suspect there may be some deeper issue at work that I am not aware of. When I have time to investigate further I shall update this post. Unfortunately I don’t have time to look into ‘solved’ bugs today.

UPDATED 2008-12-26: in general, all AppKit code should be called on the main thread.