unix - executing one php script at a time from a script list -

i have web application user can choose list of scripts execute , executions added table in mysql , each 1 have own state "pending,"success" ,"failed" or "in progress" user can choose stop execution.

the problem 1 script can executed @ same time others have wait until finished.

my environement linux (ubuntu) , scripts in php though doing crontab executes php script , php script grab informations sql table , search if there other execution looking if there there execution "in progress" state if there 1 exit,otherwise execute other execution having pending state. there other solution ?

it's better use atomic check. way how database not atomic after checked no other scripts running, before you've written current script starts, process may perform same check , therefore you'll 2 concurrent scripts running.

also if script terminates abnormally reason, won't update database, other scripts won't able start @ all.

more reliable way use file locking:

    $lock_file = 'some_path/process.lock';      $fd = fopen($lock_file, "w");     if (!$fd)         throw new exception("can't open file, check permissions on ".$lock_file, 1);      if (!flock($fd, lock_ex + lock_nb))         throw new alreadyrunningexception("can't lock file - script running", 0); 

then, after script job done, unlock file:

        flock($fd, lock_un);         fclose($fd);