Java Threads

[purduephotog]

We ran a neat little experiment (at least to me) to understand how the underlying threads were being executed.

Set the motor speed to one value- and then immediately set it to another value.

What we ended up with is a 'pulse' - sometimes it would hold continuous values... othertimes it would slow/speed up.

I had hoped it would help drive some points in with the programmers.

[Ether]

Originally Posted by purduephotog

We ran a neat little experiment (at least to me) to understand how the underlying threads were being executed.

Set the motor speed to one value- and then immediately set it to another value.

What we ended up with is a 'pulse' - sometimes it would hold continuous values... othertimes it would slow/speed up.

I had hoped it would help drive some points in with the programmers.

How did this help you understand how threads are being executed? What points were you hoping to drive home?

[purduephotog]

Originally Posted by Ether

How did this help you understand how threads are being executed? What points were you hoping to drive home?

Calls were being done asynchronously. That meant they were not executing in a linear fashion and you could not guarantee which would execute first.

If they executed linearly and in order, you'd have either no pulse (since the first set would be overridden when the code exited the loop) or a constant pulse rate since both calls were made in sequence, one after another, with no delays other than what the scheduler created.

Which mean the scheduler was pausing the robot.main classes and running things in the background- interrupt, so to speak, the main thread transparently. The students didn't (and still don't, I think) understand the implications of this. They think it just runs and runs and runs... they never see the pauses because they aren't presented to them.

One of the biggest issues I've had in trying to teach (and even some adults) is that just because you put two lines next to each other in the code- when dealing with hardware- you never know for certain (unless you're VERY careful) that they will execute properly. So it is always best to design with that thought in mind....