Throw early when EventLoop is modified while running

wpilibc/src/main/native/cpp/event/EventLoop.cpp

@@ -3,21 +3,39 @@
 // the WPILib BSD license file in the root directory of this project.
 
 #include "frc/event/EventLoop.h"
+#include "frc/Errors.h"
 
 using namespace frc;
 
+namespace {
+struct RunningSetter {
+  bool& m_running;
+  explicit RunningSetter(bool& running) noexcept : m_running{running} {
+    m_running = true;
+  }
+  ~RunningSetter() noexcept { m_running = false; }
+};
+}  // namespace
+
 EventLoop::EventLoop() {}
 
 void EventLoop::Bind(wpi::unique_function<void()> action) {
+  if (m_running) {
+    throw FRC_MakeError(err::Error, "Cannot bind EventLoop while it is running");
+  }
   m_bindings.emplace_back(std::move(action));
 }
 
 void EventLoop::Poll() {
+  RunningSetter runSetter{m_running};
   for (wpi::unique_function<void()>& action : m_bindings) {
     action();
   }
 }
 
 void EventLoop::Clear() {
+  if (m_running) {
+    throw FRC_MakeError(err::Error, "Cannot clear EventLoop while it is running");
+  }
   m_bindings.clear();
 }

wpilibc/src/main/native/include/frc/event/EventLoop.h

@@ -38,5 +38,6 @@ class EventLoop {
 
  private:
   std::vector<wpi::unique_function<void()>> m_bindings;
+  bool m_running;
 };
 }  // namespace frc

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

@@ -5,30 +5,43 @@
 package edu.wpi.first.wpilibj.event;
 
 import java.util.Collection;
+import java.util.ConcurrentModificationException;
 import java.util.LinkedHashSet;
 
 /**
  * A declarative way to bind a set of actions to a loop and execute them when the loop is polled.
  */
 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.
    *
    * @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();
   }
 }