http://php.he.net/manual/en/function.pcntl-fork.php says 'The reason for the MySQL "Lost Connection during query"...' like what you concluded, although they grab a new $db connection in the first for loop "} else if ( $pid ) {" I bet a child closes the one you create after the for loop while the parent is waiting in the foreach loop. In your foreach when you wait for each child, can you $db->execute($stmt, $data) AFTER you pcntl_waitpid($pid, $status) ? Just reverse the lines? I think after the wait is when the child closes the connection (since I suppose you are reusing the same connection), so it is already closed. Regards, Dwight > -----Original Message----- > From: Chris Verges [mailto:chrisv@xxxxxxxxxxxxxxxxxx] > Sent: Saturday, April 21, 2007 12:21 PM > To: php-db@xxxxxxxxxxxxx > Subject: Forking and database connections > > Hey all, > > I'm writing a PHP script that queries a database for some records, splits > the records into N number of groups of equal size, and then creates N > number > of forks where each child handles one of the groups. During the execution > of each of the child processes, I'd like the parent process to update the > status of the job in the database. > > The problem is regarding my database connection pre- and post- fork. > After > reading the pcntl_fork() page on the PHP manual, I realize that the child > process inherits the file descriptor, and if the child process closes the > connection, then it is closed in the parent process. So for each child > process (because I have more than one), I reinitialize the database link. > I > also reinitialize the database link for the parent process immediately > after > the fork. > > However, when a child process finishes, it seems like the database link > that > I reinitialized in the parent process also disconnects. I thought a fork > copied the entire heap, and therefore would make two copies of the object > instances that would remain segmented for the life of the processes. > Changes made to one copy of the heap wouldn't affect others. However, > this > doesn't seem to be the case. > > So at this point, my workaround is to wait until all of the child > processes > are finished, then re-initialize the database link, and give an updated > status message at the end rather than incrementally as child processes > finish. > > Here's some proof-of-concept code that explains what I mean: > > <?php > > /* Include PEAR::DB */ > require_once('DB.php'); > > # Database table definition > # ------------------------- > # CREATE TABLE `logs` ( > # `message` VARCHAR(128) NOT NULL > # ); > > /* Create the initial database connection for the parent process */ > $dsn = 'mysql://test:test@localhost/testdb'; > $db = DB::connect($dsn); > if ( PEAR::isError($db) ) { > die($db->getMessage() . "\n"); > } > > /* This will be the common SQL statement for all inserts */ > $sql = "INSERT INTO `logs` (`message`) VALUES (?);"; > $stmt = $db->prepare($sql); > > /* Perform a DB update */ > $data = array('Started parent process'); > $db->execute($stmt, $data); > > /* Create the child processes */ > $childPids = array(); > for ( $i = 0; $i < 5; $i++ ) { > $pid = pcntl_fork(); > if ( $pid == -1 ) { > die("\nUnable to fork!\n"); > } else if ( $pid ) { > /* Parent process */ > echo "Child process $pid created\n"; > array_push($childPids, $pid); > } else { > /* Child process */ > $myPid = posix_getpid(); > > /* Create a new database connection for the child process > */ > $db = DB::connect($dsn); > if ( PEAR::isError($db) ) { > die("\nChild process $myPid: " . $db->getMessage() > . > "\n" . $db->getDebugInfo() . "\n"); > } > > $data = array("Child process $myPid"); > $stmt = $db->prepare($sql); > $db->execute($stmt, $data); > > /* Add some latency for testing purposes */ > sleep(5); > exit; > } > } > > /* Create a new database connection for the parent process */ > $db = DB::connect($dsn); > if ( PEAR::isError($db) ) { > die("\nParent process: " . $db->getMessage() . "\n" . > $db->getDebugInfo() . "\n"); > } > > /* Wait for the children to finish */ > foreach ( $childPids as $pid ) { > $data = array("Parent process waiting on child process $pid"); > $db->execute($stmt, $data); > pcntl_waitpid($pid, $status); > $data = array("Child process $pid is finished"); > $db->execute($stmt, $data); > } > > $data = array("Parent process is finished"); > $db->execute($stmt, $data); > > ?> > > The command-line output of this code: > > $ php forking-proof-of-concept.php > Child process 27012 created > Child process 27013 created > Child process 27014 created > Child process 27015 created > Child process 27016 created > > Child process 27016: DB Error: unknown error > [nativecode=2013 ** Lost connection to MySQL server during query] ** > mysql://test:test@localhost/testdb > > And finally the database entries after running the code: > > mysql> select * from logs; > +------------------------+ > | message | > +------------------------+ > | Started parent process | > | Child process 27012 | > | Child process 27013 | > | Child process 27014 | > | Child process 27015 | > +------------------------+ > 5 rows in set (0.00 sec) > > Any help in understanding this is appreciated! > > Thanks! > Chris > > -- > PHP Database Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php -- PHP Database Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
