/**
* 保证单进程
*
* @param string $processName 进程名
* @param string $pidFile 进程文件路径
* @return boolean 是否继续执行当前进程
*/
function singleProcess($processName,$pidFile)
{
if (file_exists($pidFile) && $fp = @fopen($pidFile,"rb"))
{
flock($fp,LOCK_SH);
$last_pid = fread($fp,filesize($pidFile));
fclose($fp);

if (!empty($last_pid))
{
$command = exec("/bin/ps -p $last_pid -o command=");

if ($command == $processName)
{
return false;
}
}
}

$cur_pid = posix_getpid();

if ($fp = @fopen($pidFile,"wb"))
{
fputs($fp,$cur_pid);
ftruncate($fp,strlen($cur_pid));
fclose($fp);

return true;
}
else
{
return false;
}
}

/**
* 获取当前进程对应的Command
*
* @return string 命令及其参数
*/
function getCurrentCommand()
{
$pid = posix_getpid();
$command = exec("/bin/ps -p $pid -o command=");

return $command;
}

if (singleProcess(getCurrentCommand(),'path/to/script.pid'))
{
// code goes here
}
else
{
exit("Sorry,this script file has already been running ...\n");
}