cURL Keep-alive如何运作？

Question

I've been working on this and couldn't find a way to understand it fully.

I have this code:

 <?php
function get2($url) {
  // Create a handle.
  $handle = curl_init($url);

  // Set options...

  // Do the request.
  $ret = curlExecWithMulti($handle);

  // Do stuff with the results...

  // Destroy the handle.
  curl_close($handle);

}

function curlExecWithMulti($handle) {
  // In real life this is a class variable.
  static $multi = NULL;

  // Create a multi if necessary.
  if (empty($multi)) {
    $multi = curl_multi_init();
  }

  // Add the handle to be processed.
  curl_multi_add_handle($multi, $handle);

  // Do all the processing.
  $active = NULL;
  do {
    $ret = curl_multi_exec($multi, $active);
  } while ($ret == CURLM_CALL_MULTI_PERFORM);

  while ($active && $ret == CURLM_OK) {
    if (curl_multi_select($multi) != -1) {
      do {
         $mrc = curl_multi_exec($multi, $active);
      } while ($mrc == CURLM_CALL_MULTI_PERFORM);
    }
  }

  // Remove the handle from the multi processor.
  curl_multi_remove_handle($multi, $handle);

  return TRUE;
}

?>

The above script is doing this: I run the PHP and it creates new TCP connection, it returns data and then it closes the connection.

The server is working on HTTP 1.1 and connection: keep-alive.

What i want is if i run the script will create connection, return data and NOT close the connection and when i run the PHP script again will use that same connection (of course if that connection didn't expire after the timeout of the sever).

Is that possible with cURL ? Am I understanding the multi in cURL wrong?

Answer 1

When a program exits, all of its open sockets (indeed, all open files) are closed. There is no way to reuse a connection from one instance to another(*). You must re-open a new connection or loop within your application.

If you want to use HTTP Keep-Alive, your program must not exit.

(*) There are ways to keep a socket open inside one process and pass it to others via Unix domain sockets but that is an advanced topic I recommend against; I mention it only for completeness.