Rant on The Concept of Task Scheduler

<rant>
A few days ago; browsing Wikipedia; a small little detail caught my eye.  The .NET framework is finally getting a means to schedule tasks.  Task schedulers are nothing new (they have a fairly long history), the most prominent at the moment are Intel's Thread Building Blocks and Apple's Grand Central Dispatch + Operation Queues.

In general, the idea is very simple.

Threads + critical sections + error-prone humans writing code = race conditions + deadlocks + other "joys".

Ok.  That's not good!

The race conditions are never a good thing.  What we want is to get rid of race conditions (or eliminate their likelihood).  Race conditions arise from bad use of critical sections, such as two threads mutually blocked for each others' held resource.

Eg.  Thread A needs fish and thread B needs bread.  Thread B has the fish and won't relinquish until it has the bread.  Thread A has the bread and won't relinquish it until it has the fish.  Deadlock.

Eg.  Thread A should complete it's tasks first, but thread B manages to get started ahead of time due to a programming mistake.  Race Condition.

For deadlocks, we just need ensure that a task only starts when it has all it's resources available, and when it ends it doesn't keep a hold on any resources.

For race conditions.  We do the same; make sure that the order is properly specified.  Rather than specify a list of things to do with convoluted gates keeping everything running in order; we tell the underlying system what the order is as a tree of dependencies.

Grand Central (from my quick reading) helps with the former and a bit with the latter (it uses semaphores).  Operation Queues and Intel Thread Building Blocks focus on the latter (I'm more familiar with this model of operations).

I'd go into details of the specific APIs; but that can be found all over the web - and more coherent than I'd ever manage to write it.  And the APIs are moving targets, the concepts not so much.
</rant>