[wpilib] Add EventLoop (#4104)

This is a generic expansion of the command-based Trigger framework.

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/CommandScheduler.java

@@ -4,6 +4,8 @@
 
 package edu.wpi.first.wpilibj2.command;
 
+import static edu.wpi.first.util.ErrorMessages.requireNonNullParam;
+
 import edu.wpi.first.hal.FRCNetComm.tInstances;
 import edu.wpi.first.hal.FRCNetComm.tResourceType;
 import edu.wpi.first.hal.HAL;
@@ -15,13 +17,13 @@ import edu.wpi.first.wpilibj.RobotBase;
 import edu.wpi.first.wpilibj.RobotState;
 import edu.wpi.first.wpilibj.TimedRobot;
 import edu.wpi.first.wpilibj.Watchdog;
+import edu.wpi.first.wpilibj.event.EventLoop;
 import edu.wpi.first.wpilibj.livewindow.LiveWindow;
+import edu.wpi.first.wpilibj2.command.button.Trigger;
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
-import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -64,8 +66,9 @@ public final class CommandScheduler implements NTSendable, AutoCloseable {
   // as a list of currently-registered subsystems.
   private final Map<Subsystem, Command> m_subsystems = new LinkedHashMap<>();
 
+  private final EventLoop m_defaultButtonLoop = new EventLoop();
   // The set of currently-registered buttons that will be polled every iteration.
-  private final Collection<Runnable> m_buttons = new LinkedHashSet<>();
+  private EventLoop m_activeButtonLoop = m_defaultButtonLoop;
 
   private boolean m_disabled;
 
@@ -114,18 +117,53 @@ public final class CommandScheduler implements NTSendable, AutoCloseable {
     LiveWindow.setDisabledListener(null);
   }
 
+  /**
+   * Get the default button poll.
+   *
+   * @return a reference to the default {@link EventLoop} object polling buttons.
+   */
+  public EventLoop getDefaultButtonLoop() {
+    return m_defaultButtonLoop;
+  }
+
+  /**
+   * Get the active button poll.
+   *
+   * @return a reference to the current {@link EventLoop} object polling buttons.
+   */
+  public EventLoop getActiveButtonLoop() {
+    return m_activeButtonLoop;
+  }
+
+  /**
+   * Replace the button poll with another one.
+   *
+   * @param loop the new button polling loop object.
+   */
+  public void setActiveButtonLoop(EventLoop loop) {
+    m_activeButtonLoop =
+        requireNonNullParam(loop, "loop", "CommandScheduler" + ".replaceButtonEventLoop");
+  }
+
   /**
    * Adds a button binding to the scheduler, which will be polled to schedule commands.
    *
    * @param button The button to add
+   * @deprecated Use {@link Trigger}
    */
+  @Deprecated(since = "2023")
   public void addButton(Runnable button) {
-    m_buttons.add(button);
+    m_activeButtonLoop.bind(() -> true, button);
   }
 
-  /** Removes all button bindings from the scheduler. */
+  /**
+   * Removes all button bindings from the scheduler.
+   *
+   * @deprecated call {@link EventLoop#clear()} on {@link #getActiveButtonLoop()} directly instead.
+   */
+  @Deprecated(since = "2023")
   public void clearButtons() {
-    m_buttons.clear();
+    m_activeButtonLoop.clear();
   }
 
   /**
@@ -254,10 +292,11 @@ public final class CommandScheduler implements NTSendable, AutoCloseable {
       m_watchdog.addEpoch(subsystem.getClass().getSimpleName() + ".periodic()");
     }
 
+    // Cache the active instance to avoid concurrency problems if setActiveLoop() is called from
+    // inside the button bindings.
+    EventLoop loopCache = m_activeButtonLoop;
     // Poll buttons for new commands to add.
-    for (Runnable button : m_buttons) {
-      button.run();
-    }
+    loopCache.poll();
     m_watchdog.addEpoch("buttons.run()");
 
     m_inRunLoop = true;

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/Button.java

@@ -20,9 +20,11 @@ import java.util.function.BooleanSupplier;
  */
 public class Button extends Trigger {
   /**
-   * Default constructor; creates a button that is never pressed (unless {@link Button#get()} is
-   * overridden).
+   * Default constructor; creates a button that is never pressed.
+   *
+   * @deprecated Replace with {@code new Button(() -> false) }.
    */
+  @Deprecated(since = "2023")
   public Button() {}
 
   /**

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/InternalButton.java

@@ -4,6 +4,8 @@
 
 package edu.wpi.first.wpilibj2.command.button;
 
+import java.util.concurrent.atomic.AtomicBoolean;
+
 /**
  * This class is intended to be used within a program. The programmer can manually set its value.
  * Also includes a setting for whether or not it should invert its value.
@@ -11,8 +13,9 @@ package edu.wpi.first.wpilibj2.command.button;
  * <p>This class is provided by the NewCommands VendorDep
  */
 public class InternalButton extends Button {
-  private boolean m_pressed;
-  private boolean m_inverted;
+  // need to be references, so they can be mutated after being captured in the constructor.
+  private final AtomicBoolean m_pressed;
+  private final AtomicBoolean m_inverted;
 
   /** Creates an InternalButton that is not inverted. */
   public InternalButton() {
@@ -26,19 +29,24 @@ public class InternalButton extends Button {
    *     when set to false.
    */
   public InternalButton(boolean inverted) {
-    m_pressed = m_inverted = inverted;
+    this(new AtomicBoolean(), new AtomicBoolean(inverted));
+  }
+
+  /*
+   * Mock constructor so the AtomicBoolean objects can be constructed before the super
+   * constructor invocation.
+   */
+  private InternalButton(AtomicBoolean state, AtomicBoolean inverted) {
+    super(() -> state.get() != inverted.get());
+    this.m_pressed = state;
+    this.m_inverted = inverted;
   }
 
   public void setInverted(boolean inverted) {
-    m_inverted = inverted;
+    m_inverted.set(inverted);
   }
 
   public void setPressed(boolean pressed) {
-    m_pressed = pressed;
-  }
-
-  @Override
-  public boolean get() {
-    return m_pressed ^ m_inverted;
+    m_pressed.set(pressed);
   }
 }

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/JoystickButton.java

@@ -14,9 +14,6 @@ import edu.wpi.first.wpilibj.GenericHID;
  * <p>This class is provided by the NewCommands VendorDep
  */
 public class JoystickButton extends Button {
-  private final GenericHID m_joystick;
-  private final int m_buttonNumber;
-
   /**
    * Creates a joystick button for triggering commands.
    *
@@ -24,19 +21,7 @@ public class JoystickButton extends Button {
    * @param buttonNumber The button number (see {@link GenericHID#getRawButton(int) }
    */
   public JoystickButton(GenericHID joystick, int buttonNumber) {
+    super(() -> joystick.getRawButton(buttonNumber));
     requireNonNullParam(joystick, "joystick", "JoystickButton");
-
-    m_joystick = joystick;
-    m_buttonNumber = buttonNumber;
-  }
-
-  /**
-   * Gets the value of the joystick button.
-   *
-   * @return The value of the joystick button
-   */
-  @Override
-  public boolean get() {
-    return m_joystick.getRawButton(m_buttonNumber);
   }
 }

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/NetworkButton.java

@@ -4,6 +4,8 @@
 
 package edu.wpi.first.wpilibj2.command.button;
 
+import static edu.wpi.first.wpilibj.util.ErrorMessages.requireNonNullParam;
+
 import edu.wpi.first.networktables.NetworkTable;
 import edu.wpi.first.networktables.NetworkTableEntry;
 import edu.wpi.first.networktables.NetworkTableInstance;
@@ -14,15 +16,14 @@ import edu.wpi.first.networktables.NetworkTableInstance;
  * <p>This class is provided by the NewCommands VendorDep
  */
 public class NetworkButton extends Button {
-  private final NetworkTableEntry m_entry;
-
   /**
    * Creates a NetworkButton that commands can be bound to.
    *
    * @param entry The entry that is the value.
    */
   public NetworkButton(NetworkTableEntry entry) {
-    m_entry = entry;
+    super(() -> entry.getInstance().isConnected() && entry.getBoolean(false));
+    requireNonNullParam(entry, "entry", "NetworkButton");
   }
 
   /**
@@ -44,9 +45,4 @@ public class NetworkButton extends Button {
   public NetworkButton(String table, String field) {
     this(NetworkTableInstance.getDefault().getTable(table), field);
   }
-
-  @Override
-  public boolean get() {
-    return m_entry.getInstance().isConnected() && m_entry.getBoolean(false);
-  }
 }

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/POVButton.java

@@ -14,10 +14,6 @@ import edu.wpi.first.wpilibj.GenericHID;
  * <p>This class is provided by the NewCommands VendorDep
  */
 public class POVButton extends Button {
-  private final GenericHID m_joystick;
-  private final int m_angle;
-  private final int m_povNumber;
-
   /**
    * Creates a POV button for triggering commands.
    *
@@ -26,11 +22,8 @@ public class POVButton extends Button {
    * @param povNumber The POV number (see {@link GenericHID#getPOV(int)})
    */
   public POVButton(GenericHID joystick, int angle, int povNumber) {
+    super(() -> joystick.getPOV(povNumber) == angle);
     requireNonNullParam(joystick, "joystick", "POVButton");
-
-    m_joystick = joystick;
-    m_angle = angle;
-    m_povNumber = povNumber;
   }
 
   /**
@@ -42,14 +35,4 @@ public class POVButton extends Button {
   public POVButton(GenericHID joystick, int angle) {
     this(joystick, angle, 0);
   }
-
-  /**
-   * Checks whether the current value of the POV is the target angle.
-   *
-   * @return Whether the value of the POV matches the target angle
-   */
-  @Override
-  public boolean get() {
-    return m_joystick.getPOV(m_povNumber) == m_angle;
-  }
 }

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/button/Trigger.java

@@ -7,43 +7,58 @@ package edu.wpi.first.wpilibj2.command.button;
 import static edu.wpi.first.wpilibj.util.ErrorMessages.requireNonNullParam;
 
 import edu.wpi.first.math.filter.Debouncer;
+import edu.wpi.first.wpilibj.event.BooleanEvent;
+import edu.wpi.first.wpilibj.event.EventLoop;
 import edu.wpi.first.wpilibj2.command.Command;
 import edu.wpi.first.wpilibj2.command.CommandScheduler;
 import edu.wpi.first.wpilibj2.command.InstantCommand;
 import edu.wpi.first.wpilibj2.command.Subsystem;
+import java.util.function.BiFunction;
 import java.util.function.BooleanSupplier;
 
 /**
- * This class provides an easy way to link commands to inputs.
- *
- * <p>It is very easy to link a button to a command. For instance, you could link the trigger button
- * of a joystick to a "score" command.
- *
- * <p>It is encouraged that teams write a subclass of Trigger if they want to have something unusual
- * (for instance, if they want to react to the user holding a button while the robot is reading a
- * certain sensor input). For this, they only have to write the {@link Trigger#get()} method to get
- * the full functionality of the Trigger class.
+ * This class is a wrapper around {@link BooleanEvent}, providing an easy way to link commands to
+ * digital inputs.
  *
  * <p>This class is provided by the NewCommands VendorDep
  */
-public class Trigger implements BooleanSupplier {
-  private final BooleanSupplier m_isActive;
-
+public class Trigger extends BooleanEvent {
   /**
-   * Creates a new trigger with the given condition determining whether it is active.
+   * Creates a new trigger with the given condition/digital signal.
    *
-   * @param isActive returns whether or not the trigger should be active
+   * @param loop the loop that polls this trigger
+   * @param signal the digital signal represented.
    */
-  public Trigger(BooleanSupplier isActive) {
-    m_isActive = isActive;
+  public Trigger(EventLoop loop, BooleanSupplier signal) {
+    super(loop, signal);
   }
 
   /**
-   * Creates a new trigger that is always inactive. Useful only as a no-arg constructor for
-   * subclasses that will be overriding {@link Trigger#get()} anyway.
+   * Copies the BooleanEvent into a Trigger object.
+   *
+   * @param toCast the BooleanEvent
+   * @return a Trigger wrapping the given BooleanEvent
+   * @see BooleanEvent#castTo(BiFunction)
    */
+  public static Trigger cast(BooleanEvent toCast) {
+    return toCast.castTo(Trigger::new);
+  }
+
+  /**
+   * Creates a new trigger with the given condition/digital signal.
+   *
+   * <p>Polled by the {@link CommandScheduler#getDefaultButtonLoop() default scheduler button loop}.
+   *
+   * @param signal the digital signal represented.
+   */
+  public Trigger(BooleanSupplier signal) {
+    this(CommandScheduler.getInstance().getDefaultButtonLoop(), signal);
+  }
+
+  /** Creates a new trigger that is always inactive. */
+  @Deprecated
   public Trigger() {
-    m_isActive = () -> false;
+    this(() -> false);
   }
 
   /**
@@ -54,23 +69,11 @@ public class Trigger implements BooleanSupplier {
    * <p>Functionally identical to {@link Trigger#getAsBoolean()}.
    *
    * @return whether or not the trigger condition is active.
+   * @deprecated use {@link #getAsBoolean()}
    */
-  public boolean get() {
-    return m_isActive.getAsBoolean();
-  }
-
-  /**
-   * Returns whether or not the trigger is active.
-   *
-   * <p>This method will be called repeatedly a command is linked to the Trigger.
-   *
-   * <p>Functionally identical to {@link Trigger#get()}.
-   *
-   * @return whether or not the trigger condition is active.
-   */
-  @Override
-  public final boolean getAsBoolean() {
-    return this.get();
+  @Deprecated
+  public final boolean get() {
+    return getAsBoolean();
   }
 
   /**
@@ -83,23 +86,7 @@ public class Trigger implements BooleanSupplier {
   public Trigger whenActive(final Command command, boolean interruptible) {
     requireNonNullParam(command, "command", "whenActive");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
-
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (!m_pressedLast && pressed) {
-                  command.schedule(interruptible);
-                }
-
-                m_pressedLast = pressed;
-              }
-            });
-
+    this.rising().ifHigh(() -> command.schedule(interruptible));
     return this;
   }
 
@@ -138,24 +125,9 @@ public class Trigger implements BooleanSupplier {
   public Trigger whileActiveContinuous(final Command command, boolean interruptible) {
     requireNonNullParam(command, "command", "whileActiveContinuous");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
+    this.ifHigh(() -> command.schedule(interruptible));
+    this.falling().ifHigh(command::cancel);
 
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (pressed) {
-                  command.schedule(interruptible);
-                } else if (m_pressedLast) {
-                  command.cancel();
-                }
-
-                m_pressedLast = pressed;
-              }
-            });
     return this;
   }
 
@@ -163,7 +135,7 @@ public class Trigger implements BooleanSupplier {
    * Constantly starts the given command while the button is held.
    *
    * <p>{@link Command#schedule(boolean)} will be called repeatedly while the trigger is active, and
-   * will be canceled when the trigger becomes inactive. The command is set to be interruptible.
+   * will be canceled when the trigger becomes inactive.
    *
    * @param command the command to start
    * @return this trigger, so calls can be chained
@@ -194,24 +166,9 @@ public class Trigger implements BooleanSupplier {
   public Trigger whileActiveOnce(final Command command, boolean interruptible) {
     requireNonNullParam(command, "command", "whileActiveOnce");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
+    this.rising().ifHigh(() -> command.schedule(interruptible));
+    this.falling().ifHigh(command::cancel);
 
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (!m_pressedLast && pressed) {
-                  command.schedule(interruptible);
-                } else if (m_pressedLast && !pressed) {
-                  command.cancel();
-                }
-
-                m_pressedLast = pressed;
-              }
-            });
     return this;
   }
 
@@ -236,22 +193,8 @@ public class Trigger implements BooleanSupplier {
   public Trigger whenInactive(final Command command, boolean interruptible) {
     requireNonNullParam(command, "command", "whenInactive");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
+    this.falling().ifHigh(() -> command.schedule(interruptible));
 
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (m_pressedLast && !pressed) {
-                  command.schedule(interruptible);
-                }
-
-                m_pressedLast = pressed;
-              }
-            });
     return this;
   }
 
@@ -286,26 +229,16 @@ public class Trigger implements BooleanSupplier {
   public Trigger toggleWhenActive(final Command command, boolean interruptible) {
     requireNonNullParam(command, "command", "toggleWhenActive");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
-
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (!m_pressedLast && pressed) {
-                  if (command.isScheduled()) {
-                    command.cancel();
-                  } else {
-                    command.schedule(interruptible);
-                  }
-                }
-
-                m_pressedLast = pressed;
+    this.rising()
+        .ifHigh(
+            () -> {
+              if (command.isScheduled()) {
+                command.cancel();
+              } else {
+                command.schedule(interruptible);
               }
             });
+
     return this;
   }
 
@@ -328,85 +261,45 @@ public class Trigger implements BooleanSupplier {
   public Trigger cancelWhenActive(final Command command) {
     requireNonNullParam(command, "command", "cancelWhenActive");
 
-    CommandScheduler.getInstance()
-        .addButton(
-            new Runnable() {
-              private boolean m_pressedLast = get();
+    this.rising().ifHigh(command::cancel);
 
-              @Override
-              public void run() {
-                boolean pressed = get();
-
-                if (!m_pressedLast && pressed) {
-                  command.cancel();
-                }
-
-                m_pressedLast = pressed;
-              }
-            });
     return this;
   }
 
-  /**
-   * Composes this trigger with a boolean supplier, returning a new trigger that is active when both
-   * triggers are active.
-   *
-   * @param booleanSupplier the boolean supplier to compose with
-   * @return the trigger that is active when both triggers are active
-   */
-  public Trigger and(BooleanSupplier booleanSupplier) {
-    return new Trigger(() -> get() && booleanSupplier.getAsBoolean());
+  /* ----------- Super method type redeclarations ----------------- */
+
+  @Override
+  public Trigger and(BooleanSupplier trigger) {
+    return cast(super.and(trigger));
   }
 
-  /**
-   * Composes this trigger with a boolean supplier, returning a new trigger that is active when
-   * either trigger is active.
-   *
-   * @param booleanSupplier the boolean supplier to compose with
-   * @return the trigger that is active when either trigger is active
-   */
-  public Trigger or(BooleanSupplier booleanSupplier) {
-    return new Trigger(() -> get() || booleanSupplier.getAsBoolean());
+  @Override
+  public Trigger or(BooleanSupplier trigger) {
+    return cast(super.or(trigger));
   }
 
-  /**
-   * Creates a new trigger that is active when this trigger is inactive, i.e. that acts as the
-   * negation of this trigger.
-   *
-   * @return the negated trigger
-   */
+  @Override
   public Trigger negate() {
-    return new Trigger(() -> !get());
+    return cast(super.negate());
   }
 
-  /**
-   * Creates a new debounced trigger from this trigger - it will become active when this trigger has
-   * been active for longer than the specified period.
-   *
-   * @param seconds The debounce period.
-   * @return The debounced trigger (rising edges debounced only)
-   */
+  @Override
   public Trigger debounce(double seconds) {
     return debounce(seconds, Debouncer.DebounceType.kRising);
   }
 
-  /**
-   * Creates a new debounced trigger from this trigger - it will become active when this trigger has
-   * been active for longer than the specified period.
-   *
-   * @param seconds The debounce period.
-   * @param type The debounce type.
-   * @return The debounced trigger.
-   */
+  @Override
   public Trigger debounce(double seconds, Debouncer.DebounceType type) {
-    return new Trigger(
-        new BooleanSupplier() {
-          Debouncer m_debouncer = new Debouncer(seconds, type);
+    return cast(super.debounce(seconds, type));
+  }
 
-          @Override
-          public boolean getAsBoolean() {
-            return m_debouncer.calculate(get());
-          }
-        });
+  @Override
+  public Trigger rising() {
+    return cast(super.rising());
+  }
+
+  @Override
+  public Trigger falling() {
+    return cast(super.falling());
   }
 }