Connecting Several PHP Processes To The Same MySQL Transaction

class DBHandler
{
	private $link;
	private $result;
	private $sem;
 
	const SEMKEY = '123456';
 
	public function __construct($host, $dbname, $user, $pass, $new_link = false, $client_flags = 0)
	{
		$this->link = mysql_connect($host, $user, $pass, $new_link, $client_flags);
		if (!$this->link)
			throw new Exception ('Could not connect to db. MySQL error was: '. mysql_error());
		$isDb = mysql_select_db($dbname,$this->link);
		if (!$isDb)
			throw new Exception ('Could not select db. MySQL error was: '. mysql_error());
	}
 
	private function enterSemaphore()
	{
		$this->sem = sem_get(self::SEMKEY,1);
		sem_acquire($this->sem);
	}
 
	private function exitSemaphore()
	{
		sem_release($this->sem);
	}
 
 
	public function query($sql)
	{
		$this->enterSemaphore();
 
		$this->result = mysql_unbuffered_query($sql, $this->link);
		if (!$this->result)
			throw new Exception ('Could not query: {' . $sql . '}. MySQL error was: '. mysql_error());
		if ($this->result === true)
		{
			// INSERT, UPDATE, etc..., no result set
			$ret = true;
		}
		else
		{
			// SELECT etc..., we have a result set
			$retArray = array();
			while ($row = mysql_fetch_assoc($this->result))
				$retArray[] = $row;
			mysql_free_result($this->result);
			$ret = $retArray;
		}
 
		$this->exitSemaphore();
 
		return $ret;
	}
 
	public function beginTransaction()
	{
		$this->query('SET AUTOCOMMIT = 0');
		$this->query('SET NAMES utf8');
		$this->query('START TRANSACTION');
	}
 
	public function rollback()
	{
		$this->query('ROLLBACK');
	}
 
	public function commit()
	{
		$this->query('COMMIT');
	}
}

$pid = 'initial';
$maxProcs = $argv[1];
if (!$maxProcs)
{
	 $maxProcs = 3;
}
$runningProcs = array(); // will be $runningProcs[pid] = status;
define('PRIORITY_SUCCESS','-20');
define('PRIORITY_FAILURE','-19');
 
try 
{
	$dbh = new DBHandler(DBHOST,DBNAME,DBUSER,DBPASS);
 
	$dbh->beginTransaction();
 
		// fork all needed children
		$currentProcs = 0;
		while ( ($pid) && ($currentProcs < $maxProcs))
		{
			$pid = pcntl_fork();
			$currentProcs++;
			$runningProcs[$pid] = 0;
		}
 
		if ($pid==-1)
		{
			throw new Exception ("fork failed");
		}
		elseif ($pid)
		{
			// parent
			echo "+++ in parent +++\n";
			echo "+++ children are: " . implode(",",array_keys($runningProcs)) . "\n";
 
			// wait for children
			// NOTE -- here we do it with priority signaling
			// @TBD -- posix signaling or IPC signaling.
			while (in_array(0,$runningProcs))
			{
				if (in_array(PRIORITY_FAILURE,$runningProcs))
				{
					echo "+++ some child failed, finish waiting for children +++\n";
					break;
				}
				foreach ($runningProcs as $child_pid => $status)
				{
					$runningProcs[$child_pid] = pcntl_getpriority($child_pid);
					echo "+++ children status: $child_pid, $status +++\n";
				}
				echo "\n";
				sleep(1);
			}
 
			echo "+++ checking if should commit or rollback +++\n";
			if (in_array(PRIORITY_FAILURE,$runningProcs) || in_array(0,$runningProcs))
			{		
				echo "+++ some child had problem! rollback! +++\n";
				$dbh->rollback();
			}
			else
			{
				echo "+++ all my sons successful! committing! +++\n";
				$dbh->commit();
			}
 
			// signal all children to exit
			foreach ($runningProcs as $child_pid => $status)
			{
				echo "+++ killing child $child_pid +++\n";
				posix_kill($child_pid,SIGTERM);
			}
		}
		else
		{
			// child
			$mypid = getmypid();
			echo "--- in child $mypid ---\n";
			//sleep(1);
			echo "--- child $mypid current priority is " . pcntl_getpriority() . " ---\n";
 
			// NOTE -- following queries do not work, for example only
			$dbh->query("select ...");
 
			echo "--- child $mypid finished, setting priority to success and halting ---\n";
			pcntl_setpriority(PRIORITY_SUCCESS);
			while (true)
			{
				echo "--- child $mypid waiting to be killed ---\n";
				sleep(1);
			}
		}
 
} 
catch (Exception $e) 
{
	// output error
	print "Error!: " . $e->getMessage() . "\n";
 
	// if parent -- rollback, signal children to exit
	// if child  -- make priority failure to signal
	if ($pid)
	{
		// rollback
		$dbh->rollBack();
		foreach ($runningProcs as $child_pid => $status)
			posix_kill($child_pid,SIGTERM);
	}
	else
	{
		pcntl_setpriority(PRIORITY_FAILURE);
		$mypid = getmypid();
		while (true)
		{
			echo "--- child $mypid waiting to be killed ---\n";
			sleep(1);
		}
	}
 
}