Question

I need to put on a php script that has to serve only one request at a time. That is, if a user requests the page, it must not serve him until a previous request is not completely handled.

I would play with application variables in order to accomplish that, but I see that php doesn’t have anything like that, if I well understood.

I tried to use apc then, putting together this code:

<?php

  while (apc_fetch('foo')) {
    echo "waiting...\n";
    sleep(1);
  }

  $foo = true;
  apc_store('foo', $foo);

  echo "results.";
  sleep(10);

  apc_delete('foo');

?>

but if I open twice this page, what I see is just results. in both. I was expecting to read some waiting... as well, since when I load the page for the second time, the first one should have set foo to true.

Is this a legit (but mistaken) use of apc? Am I using the wrong tool?

Answer 1

I don’t like to answer to my own questions, but in the end this is the most simple way I found to do what I wanted:

<?php

$fp = fopen("lock.txt", "r");

if (flock($fp, LOCK_EX)) {  // acquire

  echo "processing...";

  //if (isset($_GET['sleep'])) sleep(5); // decomment this line to test:
                                         // load "script.php?sleep=1" and then
                                         // load "script.php". The second page will
                                         // wait until the first one ends.

  flock($fp, LOCK_UN); // release

} else {
  // exception handling
  echo "ERROR: unable to flock()";
}

fclose($fp);

?>