[wpilib] Make BooleanEvent more consistent (#5436)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>
Co-authored-by: Joseph Eng <91924258+KangarooKoala@users.noreply.github.com>

wpilibj/src/main/java/edu/wpi/first/wpilibj/event/BooleanEvent.java

@@ -7,6 +7,7 @@ package edu.wpi.first.wpilibj.event;
 import static edu.wpi.first.util.ErrorMessages.requireNonNullParam;
 
 import edu.wpi.first.math.filter.Debouncer;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiFunction;
 import java.util.function.BooleanSupplier;
 
@@ -28,6 +29,9 @@ public class BooleanEvent implements BooleanSupplier {
   /** Condition. */
   private final BooleanSupplier m_signal;
 
+  /** The state of the condition in the current loop poll. Nightmare to manage. */
+  private final AtomicBoolean m_state = new AtomicBoolean(false);
+
   /**
    * Creates a new event with the given signal determining whether it is active.
    *
@@ -37,16 +41,19 @@ public class BooleanEvent implements BooleanSupplier {
   public BooleanEvent(EventLoop loop, BooleanSupplier signal) {
     m_loop = requireNonNullParam(loop, "loop", "BooleanEvent");
     m_signal = requireNonNullParam(signal, "signal", "BooleanEvent");
+    m_state.set(m_signal.getAsBoolean());
+    m_loop.bind(() -> m_state.set(m_signal.getAsBoolean()));
   }
 
   /**
-   * Check the state of this signal (high or low).
+   * Check the state of this signal (high or low) as of the last loop poll.
    *
-   * @return true for the high state, false for the low state.
+   * @return true for the high state, false for the low state. If the event was never polled, it
+   *     returns the state at event construction.
    */
   @Override
   public final boolean getAsBoolean() {
-    return m_signal.getAsBoolean();
+    return m_state.get();
   }
 
   /**
@@ -57,7 +64,7 @@ public class BooleanEvent implements BooleanSupplier {
   public final void ifHigh(Runnable action) {
     m_loop.bind(
         () -> {
-          if (m_signal.getAsBoolean()) {
+          if (m_state.get()) {
             action.run();
           }
         });
@@ -72,11 +79,11 @@ public class BooleanEvent implements BooleanSupplier {
     return new BooleanEvent(
         m_loop,
         new BooleanSupplier() {
-          private boolean m_previous = m_signal.getAsBoolean();
+          private boolean m_previous = m_state.get();
 
           @Override
           public boolean getAsBoolean() {
-            boolean present = m_signal.getAsBoolean();
+            boolean present = m_state.get();
             boolean ret = !m_previous && present;
             m_previous = present;
             return ret;
@@ -93,11 +100,11 @@ public class BooleanEvent implements BooleanSupplier {
     return new BooleanEvent(
         m_loop,
         new BooleanSupplier() {
-          private boolean m_previous = m_signal.getAsBoolean();
+          private boolean m_previous = m_state.get();
 
           @Override
           public boolean getAsBoolean() {
-            boolean present = m_signal.getAsBoolean();
+            boolean present = m_state.get();
             boolean ret = m_previous && !present;
             m_previous = present;
             return ret;
@@ -132,7 +139,7 @@ public class BooleanEvent implements BooleanSupplier {
 
           @Override
           public boolean getAsBoolean() {
-            return m_debouncer.calculate(m_signal.getAsBoolean());
+            return m_debouncer.calculate(m_state.get());
           }
         });
   }
@@ -144,35 +151,37 @@ public class BooleanEvent implements BooleanSupplier {
    * @return the negated event
    */
   public BooleanEvent negate() {
-    return new BooleanEvent(m_loop, () -> !m_signal.getAsBoolean());
+    return new BooleanEvent(m_loop, () -> !m_state.get());
   }
 
   /**
    * Composes this event with another event, returning a new signal that is in the high state when
    * both signals are in the high state.
    *
-   * <p>The new event will use this event's polling loop.
+   * <p>The events must use the same event loop. If the events use different event loops, the
+   * composed signal won't update until both loops are polled.
    *
    * @param other the event to compose with
    * @return the event that is active when both events are active
    */
   public BooleanEvent and(BooleanSupplier other) {
     requireNonNullParam(other, "other", "and");
-    return new BooleanEvent(m_loop, () -> m_signal.getAsBoolean() && other.getAsBoolean());
+    return new BooleanEvent(m_loop, () -> m_state.get() && other.getAsBoolean());
   }
 
   /**
    * Composes this event with another event, returning a new signal that is high when either signal
    * is high.
    *
-   * <p>The new event will use this event's polling loop.
+   * <p>The events must use the same event loop. If the events use different event loops, the
+   * composed signal won't update until both loops are polled.
    *
    * @param other the event to compose with
    * @return a signal that is high when either signal is high.
    */
   public BooleanEvent or(BooleanSupplier other) {
     requireNonNullParam(other, "other", "or");
-    return new BooleanEvent(m_loop, () -> m_signal.getAsBoolean() || other.getAsBoolean());
+    return new BooleanEvent(m_loop, () -> m_state.get() || other.getAsBoolean());
   }
 
   /**
@@ -185,6 +194,6 @@ public class BooleanEvent implements BooleanSupplier {
    * @return an instance of the subclass.
    */
   public <T extends BooleanSupplier> T castTo(BiFunction<EventLoop, BooleanSupplier, T> ctor) {
-    return ctor.apply(m_loop, m_signal);
+    return ctor.apply(m_loop, m_state::get);
   }
 }