Function to detect number of CPUs in PHP

num-cpus.php

<?php

/**
 * Copyright © 2011 Erin Millard
 */

/**
 * Returns the number of available CPU cores
 * 
 *  Should work for Linux, Windows, Mac & BSD
 * 
 * @return integer 
 */
function num_cpus()
{
  $numCpus = 1;

  if (is_file('/proc/cpuinfo'))
  {
    $cpuinfo = file_get_contents('/proc/cpuinfo');
    preg_match_all('/^processor/m', $cpuinfo, $matches);

    $numCpus = count($matches[0]);
  }
  else if ('WIN' == strtoupper(substr(PHP_OS, 0, 3)))
  {
    $process = @popen('wmic cpu get NumberOfCores', 'rb');

    if (false !== $process)
    {
      fgets($process);
      $numCpus = intval(fgets($process));

      pclose($process);
    }
  }
  else
  {
    $process = @popen('sysctl -a', 'rb');

    if (false !== $process)
    {
      $output = stream_get_contents($process);

      preg_match('/hw.ncpu: (\d+)/', $output, $matches);
      if ($matches)
      {
        $numCpus = intval($matches[1][0]);
      }

      pclose($process);
    }
  }
  
  return $numCpus;
}

echo num_cpus().PHP_EOL;

I would cache the number of CPUs returned, at least with static:

    static $numCpus;
    if ( !isset($numCpus) ) {
    ...
    }
    return $numCpus;

@ezzatron Is there a license (MIT, GPLv3, etc.) for this piece of code?

@duzun then at least reduce nesting a bit:

static $numCpus;
if (isset($numCpus))
    return $numCpus;

... // OP's code

return $numCpus;

For something under Apache license there is always Zeta Components SystemInfo: https://github.com/zetacomponents/SystemInformation/blob/master/src/info.php#L65-L73

@adduc just made a copyLEFT version, you can fork it and add whatever license you'd like, https://gist.github.com/divinity76/01ef9ca99c111565a72d3a8a6e42f7fb