saintsrobotics/corebot-2017

Our robot code for 2017, featuring coroutines

corebot-2017's Issues

A while loop in a task will continue running even after disabling and reenabling?

We had a bug on Saturday. What happened is if we disabled in the middle of our autonomous code and then reenabled, the motors would sometimes continue at the same values they had before and would not accept input. I found a tricky infinite loop and fixed it, and from then on we didn't see the issue again:

581d9e3#diff-2094e283bb3890e841571da6ac09c6b1R133

Here's my attempt at figuring out what the issue is.

Consider the following TaskRunner and example task:

new TaskRunner(
    new ExampleTask(),
    new UpdateMotorsTask()
);

public class ExampleTask extends Task {
    public void run() {
        while (true) {
            Robot.motors.allDrive.set(1.0);
            wait.forFrame();
        }
    }
}

If you enable the robot, this task will run and work fine. However, if you make the logic slightly more insidious:

public class ExampleTask extends Task {
    public void run() {
        while (true) {
            if (condition) {
                continue;
            }
            Robot.motors.allDrive.set(1.0);
            wait.forFrame();
        }
    }
}

If condition is true, then this task will get caught in an infinite loop and will not ever wait, and thus will not ever terminate. This loop will continue to run as long as condition is true...

Actually, I can't seem to get something that'd replicate the issue we saw on Saturday.

Repeating tasks never exit

There is currently no task cancellation policy. For example, RepeatingTask.run method should return when the robot is disabled and/or switches out of the current mode (autonomous/teleop). Currently it never returns (has a while(true)). The iterator logic thread (collection thread) will never exit - will just be stuck waiting for a yield that never returns. It's not clean and it will leak threads each time there is a mode switch (when a new taskRunner instance is created, leaving the old one still hanging around stuck in some Task's yield call.) Suggestion: cancel task, and yield code should throw an exception. This support may already be there in the underlying Generator framework -need to investigate.

Cannot dynamically add tasks

Cannot currently dynamically add a Task (after teleop/autonomous operation mode has started). Workaround: add all anticipated tasks during init, and if needed a Task yields until it is triggered by some future "start" condition. Can get tricky if the logical task needs to be run multiple times. We should check if this scenario can possibly arise for the competition robot, and if so try to try to test a comparable scenario earlier rather than later.