How do I implement basic "Long Polling"?

Here's an example of how you can implement Long Polling in PHP:

<?php

// Define a function to simulate getting new data
function getNewData()
{
  // Simulate getting new data
  $newData = "New data is available!";
  return $newData;
}

// Set maximum time the server should keep the connection open
$maxWaitTime = 30; // seconds
$startTime = time();

// Keep the connection open until new data is available or the maximum wait time is reached
while (true) {
  // Check for new data
  $newData = getNewData();
  if ($newData) {
    // Send new data to the client
    echo $newData;
    break;
  }

  // Check if the maximum wait time has been reached
  $waitTime = time() - $startTime;
  if ($waitTime > $maxWaitTime) {
    break;
  }

  // Sleep for a short period of time before checking for new data again
  usleep(100000); // 100ms
}

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This code will keep the connection open until new data is available or the maximum wait time has been reached. The client can then send a new request to the server to get any new data that has become available since the previous request.

You can use this technique to create a real-time chat application, real-time notifications system, or any other type of web application that requires real-time behavior.

It's important to note that Long Polling can put a lot of strain on the server, as it requires the server to keep connections open for potentially long periods of time. If you expect your application to have a high volume of traffic, you may want to consider using a more efficient technique such as WebSockets or Server-Sent Events.