For Wampp (Windows)
-----------------------------------------------------------------------------------
1.  Find out what is your 'PHP Extension Build' version by using phpinfo(). You can use this - http://localhost/?phpinfo=1
2.  Download the pthreads that matches your php version (32 bit or 64 bit) and php extension build (currently used VC11). Use this link for download - http://windows.php.net/downloads/pecl/releases/pthreads/ 
3.  Extract the zip -
      Move php_pthreads.dll to the 'bin\php\ext\' directory.
      Move pthreadVC2.dll to the 'bin\php\' directory.
      Move pthreadVC2.dll to the 'bin\apache\bin' directory.
      Move pthreadVC2.dll to the 'C:\windows\system32' directory.
4.  Open php\php.ini and add
      extension=php_pthreads.dll
Now restart server and you are done. Thanks.