`Trigger.getAsBoolean()` behavior has been changed from passing through
the underlying boolean supplier to returning the latest cached signal as
determined by the most recent call to `poll()`. This allows rising and
falling edge triggers to have a consistent return value over an entire
polling cycle, rather than only being high for the _first_ check in a
cycle.
Closes#8309
Commands are no longer able to outlive their schedule-site's scope,
regardless of how they were scheduled (set as a default command, bound
to a trigger, or manually scheduled)
As a consequence, default commands need better tracking so the default
command setting can be released when their scope exits and the next-most
appropriate default command can be rescheduled (eg, an opmode sets a
default command, then the globally-scoped default is restored when the
opmode exits). Some complexity is required here to make it work well for
edge cases.
Like `schedule()`, `setDefaultCommand()` will immediately start the new
default command if called inside of another command to avoid 1-loop
delays. However, this does not apply when called by the _current_
default command, as it would result in attempting to cancel the default
command while it's mounted (which is impossible and would throw an
exception)
```java
class Robot extends OpModeRobot {
final Drive drive = new Drive();
final CommandXboxController controller = new CommandXboxController(1);
public Robot() {
// global default command, active unless overridden in an opmode or command
drive.setDefaultCommand(drive.stop());
// global trigger binding, always active
controller.rightBumper().onTrue(drive.setX());
}
}
@Teleop
class ExampleOpMode extends PeriodicOpMode {
public ExampleOpMode(Robot robot) {
// opmode-specific default command
robot.drive.setDefaultCommand(robot.drive.operatorControl(robot.controller));
// opmode-specific binding
robot.controller.leftBumper().whileTrue(robot.drive.stop());
// opmode-specific binding that takes precedence over the global binding
// because it happens last; it "wins out" over the `setX()` binding
robot.controller.rightBumper().onTrue(robot.drive.selfTest());
}
@Override
public void periodic() {
Scheduler.getDefault().run();
}
}
```
The framework fundamentally relies on the continuation API added in Java 21 (which is currently internal to the JDK). Continuations allow for call stacks to be saved to the heap and resumed later.
The async framework allows command bodies to be written in an imperative style. However, an async command will need to be actively cooperative and periodically call coroutine.yield() in loops to yield control back to the command scheduler to let it process other commands.
There are also some other additions like priority levels (as opposed to a blanket yes/no for ignoring incoming commands), factories requiring names be provided for commands, and the scheduler tracking all running commands and not just the highest-level groups. However, those changes aren't unique to an async framework, and could just as easily be used in a traditional command framework.
