Actually I suppose you need to loop with foreach to wait on all children before attempting any $db->execute, then after your foreach loop, get your $db and execute. Regards, Dwight > -----Original Message----- > From: Dwight Altman [mailto:dwight@xxxxxxxxxxxx] > Sent: Monday, April 23, 2007 10:09 AM > To: 'php-db@xxxxxxxxxxxxx' > Subject: RE: Forking and database connections > > 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
