Copilot

Great questions! Handling race conditions and tab crashes are crucial for ensuring the robustness of your solution. Here are some strategies to address these issues:
Preventing Race ConditionsTo prevent multiple tabs from simultaneously trying to become the controller, you can use a combination of localStorage and a timestamp-based locking mechanism. Here's how you can do it:

• Locking Mechanism: Use localStorage to create a lock with a timestamp.
• Atomic Operations: Ensure that the operations to check and set the controller are atomic.
  Example Implementation

const channel = new BroadcastChannel('tab-communication');
let isController = false;

function becomeController() {
  isController = true;
  const eventSource = new EventSource('/events');
  eventSource.onmessage = (event) => {
    channel.postMessage(event.data);
  };
  window.addEventListener('beforeunload', () => {
    localStorage.removeItem('controller');
    channel.postMessage('controller-closed');
  });
}

function checkController() {
  const now = Date.now();
  const controller = localStorage.getItem('controller');
  if (!controller || now - parseInt(controller) > 5000) { // 5 seconds timeout
    localStorage.setItem('controller', now.toString());
    becomeController();
  }
}

checkController();

channel.onmessage = (message) => {
  if (message.data === 'controller-closed' && !isController) {
    checkController();
  } else if (!isController) {
    // Handle the event data
    console.log('Received event:', message.data);
  }
};

Handling Tab CrashesTo handle situations where the controller tab crashes and the beforeunload event is not called, you can implement a heartbeat mechanism:

• Heartbeat Mechanism: The controller tab periodically updates a timestamp in localStorage.
• Timeout Detection: Other tabs check this timestamp to detect if the controller tab has crashed.
  Example Implementation

const HEARTBEAT_INTERVAL = 2000; // 2 seconds
const HEARTBEAT_TIMEOUT = 5000; // 5 seconds

function startHeartbeat() {
  setInterval(() => {
    if (isController) {
      localStorage.setItem('controller-heartbeat', Date.now().toString());
    }
  }, HEARTBEAT_INTERVAL);
}

function checkController() {
  const now = Date.now();
  const controller = localStorage.getItem('controller');
  const heartbeat = localStorage.getItem('controller-heartbeat');
  if (!controller || !heartbeat || now - parseInt(heartbeat) > HEARTBEAT_TIMEOUT) {
    localStorage.setItem('controller', now.toString());
    becomeController();
  }
}

startHeartbeat();
checkController();

channel.onmessage = (message) => {
  if (message.data === 'controller-closed' && !isController) {
    checkController();
  } else if (!isController) {
    // Handle the event data
    console.log('Received event:', message.data);
  }
};

Key Points- Locking Mechanism: Prevents race conditions by using a timestamp-based lock.

• Heartbeat Mechanism: Ensures that a new controller is elected if the current one crashes.
• Timeout Detection: Other tabs detect if the controller tab has stopped updating the heartbeat.
  These strategies should help you create a robust solution for managing multiple tabs with a single controller for server-sent events. If you have any more questions or need further assistance, feel free to ask!