EventLoop.java

// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
 
package org.wpilib.event;
 
import java.util.ConcurrentModificationException;
import java.util.LinkedHashSet;
import org.wpilib.util.container.WeakLinkedHashSet;

public final class EventLoop {
  // Keep all bindings in one insertion-ordered collection for polling.
  private final WeakLinkedHashSet<Runnable> m_bindings = new WeakLinkedHashSet<>();
  // Keep strong references for strongly bound actions to prevent garbage collection.
  private final LinkedHashSet<Runnable> m_strongBindings = new LinkedHashSet<>();
  private boolean m_running;

  public EventLoop() {}

  public void bind(Runnable action) {
    if (m_running) {
      throw new ConcurrentModificationException("Cannot bind EventLoop while it is running");
    }
    m_bindings.add(action);
    m_strongBindings.add(action);
  }

  public void bindWeak(Runnable action) {
    if (m_running) {
      throw new ConcurrentModificationException("Cannot bind EventLoop while it is running");
    }
    m_bindings.add(action);
  }

  public boolean isBound(Runnable action) {
    return m_bindings.contains(action);
  }

  public void unbind(Runnable action) {
    if (m_running) {
      throw new ConcurrentModificationException("Cannot unbind EventLoop while it is running");
    }
    m_bindings.remove(action);
    m_strongBindings.remove(action);
  }

  @SuppressWarnings("PMD.UnusedAssignment")
  public void poll() {
    try {
      m_running = true;
      m_bindings.forEach(Runnable::run);
    } finally {
      m_running = false;
    }
  }

  public void clear() {
    if (m_running) {
      throw new ConcurrentModificationException("Cannot clear EventLoop while it is running");
    }
    m_bindings.clear();
    m_strongBindings.clear();
  }
}