PHP: １度だけ実行

これを

<meta http-equiv="refresh" content="1">

すると, ソルバ実行中のstdout/stderrをリアルタイムっぽく表示してくれる.

<?php
session_start();
if ( isset($_SESSION['status']) && $_SESSION['status'] == 'done' ) {
  header("Location: result.php");
  exit;
}

if ( isset($_POST['job']) ) {
  /* execute once */
  $command = solve_command();
  $buffer = uniq_name();
  system($command . " > " . $buffer . " 2>&1 " . "&");
  $_SESSION['command'] = $command;
  $_SESSION['buffer']  = $buffer;
  $_SESSION['status']  = 'running';
} else {
  $command = $_SESSION['command'];
  $buffer  = $_SESSION['buffer'];
  $fp = fopen($buffer, "r");
  if ( !$fp ) {
    die("cannot open buffering file.");
  }
  echo "<pre>";
  fpassthru($fp);
  echo "</pre>";
  $_SESSION['status'] = 'done';
}
?>