[wpilib, examples] Cleanup PotentiometerPID, Ultrasonic, UltrasonicPID examples (#4893)

Fix C++ Ultrasonic to return correct units.

wpilibj/src/main/java/edu/wpi/first/wpilibj/Ultrasonic.java

@@ -90,9 +90,6 @@ public class Ultrasonic implements Sendable, AutoCloseable {
       m_pingChannel.setSimDevice(m_simDevice);
       m_echoChannel.setSimDevice(m_simDevice);
     }
-    if (m_task == null) {
-      m_task = new UltrasonicChecker();
-    }
     final boolean originalMode = m_automaticEnabled;
     setAutomaticMode(false); // kill task when adding a new sensor
     m_sensors.add(this);
@@ -202,7 +199,7 @@ public class Ultrasonic implements Sendable, AutoCloseable {
    *     sensors fire at the same time. If another scheduling algorithm is preferred, it can be
    *     implemented by pinging the sensors manually and waiting for the results to come back.
    */
-  public static void setAutomaticMode(boolean enabling) {
+  public static synchronized void setAutomaticMode(boolean enabling) {
     if (enabling == m_automaticEnabled) {
       return; // ignore the case of no change
     }
@@ -217,14 +214,18 @@ public class Ultrasonic implements Sendable, AutoCloseable {
       }
 
       // Start round robin task
+      m_task = new UltrasonicChecker();
       m_task.start();
     } else {
-      // Wait for background task to stop running
-      try {
-        m_task.join();
-      } catch (InterruptedException ex) {
-        Thread.currentThread().interrupt();
-        ex.printStackTrace();
+      if (m_task != null) {
+        // Wait for background task to stop running
+        try {
+          m_task.join();
+          m_task = null;
+        } catch (InterruptedException ex) {
+          Thread.currentThread().interrupt();
+          ex.printStackTrace();
+        }
       }
 
       /* Clear all the counters (data now invalid) since automatic mode is

wpilibj/src/main/java/edu/wpi/first/wpilibj/simulation/UltrasonicSim.java

@@ -9,6 +9,7 @@ import edu.wpi.first.hal.SimDouble;
 import edu.wpi.first.math.util.Units;
 import edu.wpi.first.wpilibj.Ultrasonic;
 
+/** Class to control a simulated {@link edu.wpi.first.wpilibj.Ultrasonic}. */
 public class UltrasonicSim {
   private final SimBoolean m_simRangeValid;
   private final SimDouble m_simRange;
@@ -19,7 +20,18 @@ public class UltrasonicSim {
    * @param ultrasonic The real ultrasonic to simulate
    */
   public UltrasonicSim(Ultrasonic ultrasonic) {
-    SimDeviceSim simDevice = new SimDeviceSim("Ultrasonic", ultrasonic.getEchoChannel());
+    // ping parameter is unused
+    this(-1, ultrasonic.getEchoChannel());
+  }
+
+  /**
+   * Constructor.
+   *
+   * @param ping unused.
+   * @param echo the ultrasonic's echo channel.
+   */
+  public UltrasonicSim(@SuppressWarnings("unused") int ping, int echo) {
+    SimDeviceSim simDevice = new SimDeviceSim("Ultrasonic", echo);
     m_simRangeValid = simDevice.getBoolean("Range Valid");
     m_simRange = simDevice.getDouble("Range (in)");
   }

wpilibj/src/test/java/edu/wpi/first/wpilibj/UltrasonicTest.java

@@ -4,12 +4,15 @@
 
 package edu.wpi.first.wpilibj;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import edu.wpi.first.wpilibj.simulation.UltrasonicSim;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 class UltrasonicTest {
   @Test
@@ -28,4 +31,23 @@ class UltrasonicTest {
       assertEquals(0, ultrasonic.getRangeInches());
     }
   }
+
+  @Test
+  void automaticModeToggle() {
+    try (@SuppressWarnings("unused")
+        Ultrasonic ultrasonic = new Ultrasonic(0, 1)) {
+      assertDoesNotThrow(
+          () -> {
+            Ultrasonic.setAutomaticMode(true);
+            Ultrasonic.setAutomaticMode(false);
+            Ultrasonic.setAutomaticMode(true);
+          });
+    }
+  }
+
+  @ValueSource(booleans = {true, false})
+  @ParameterizedTest
+  void automaticModeWithZeroInstances(boolean enabling) {
+    assertDoesNotThrow(() -> Ultrasonic.setAutomaticMode(enabling));
+  }
 }