[wpilib] Throw early when EventLoop is modified while running (#6115)

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

@@ -5,6 +5,7 @@
 package edu.wpi.first.wpilibj.event;
 
 import java.util.Collection;
+import java.util.ConcurrentModificationException;
 import java.util.LinkedHashSet;
 
 /**
@@ -12,6 +13,7 @@ import java.util.LinkedHashSet;
  */
 public final class EventLoop {
   private final Collection<Runnable> m_bindings = new LinkedHashSet<>();
+  private boolean m_running;
 
   /**
    * Bind a new action to run when the loop is polled.
@@ -19,16 +21,27 @@ public final class EventLoop {
    * @param action the action to run.
    */
   public void bind(Runnable action) {
+    if (m_running) {
+      throw new ConcurrentModificationException("Cannot bind EventLoop while it is running");
+    }
     m_bindings.add(action);
   }
 
   /** Poll all bindings. */
   public void poll() {
-    m_bindings.forEach(Runnable::run);
+    try {
+      m_running = true;
+      m_bindings.forEach(Runnable::run);
+    } finally {
+      m_running = false;
+    }
   }
 
   /** Clear all bindings. */
   public void clear() {
+    if (m_running) {
+      throw new ConcurrentModificationException("Cannot clear EventLoop while it is running");
+    }
     m_bindings.clear();
   }
 }