![$pid = pcntl_fork();
switch($pid)
{
case 0:
// Child process
call_user_func($callback, $data);
posix_kill(posix_getppid(), SIGCHLD);
exit;
case -1:
// Parent process, fork failed
throw new Exception("Out of memory!");
default:
// Parent process, fork succeeded
$processes[$pid] = TRUE;
}
Wednesday, December 5, 12](https://image.slidesharecdn.com/multiprocessing-121205194400-phpapp02/75/Multi-tasking-in-PHP-20-2048.jpg)
![function reap_child()
{
// Check if any child process has terminated,
// and if so remove it from memory
$pid = pcntl_wait($status, WNOHANG);
if ($pid < 0)
{
throw new Exception("Out of memory");
}
elseif ($pid > 0)
{
unset($processes[$pid]);
}
}
Wednesday, December 5, 12](https://image.slidesharecdn.com/multiprocessing-121205194400-phpapp02/75/Multi-tasking-in-PHP-22-2048.jpg)
Uploaded byJonathon Hill
Multi-tasking in PHP
The document discusses multi-tasking in PHP using multiprocessing. It describes how to fork child processes from a parent process to perform asynchronous tasks in parallel. It covers using signals to communicate between processes and reaping zombie processes. Examples are provided to illustrate how to fork processes, define signal handlers, and avoid race conditions using semaphores to protect shared resources.
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Multi-tasking in PHP
- 1. Multi-tasking in PHP Wednesday,December 5, 12
- 2. About Me • Formerly CTO for Company52 • Currently work at Brandmovers on Northside Drive • Self-taught • Full-time geek since 2007 Wednesday, December 5, 12
- 3.
- 4. Use Cases • System resources are not the bottleneck • Batch processing involving an API: • E-Mail • Geocoding • Electronic billing • Daemons Wednesday, December 5, 12
- 5. Alternatives • Gearman • curl_multi_* • Other scripting languages Wednesday, December 5, 12
- 6.
- 7. Two ways tomulti-task Multi-processing Multi-threading Separate memory Shared memory Errors are isolated Errors are not isolated Separate permissions Same permissions Linux/UNIX Windows Wednesday, December 5, 12
- 8. Multiprocessing Multithreading Process 1 program Process 1 program Thread 1 state: virtual memory PC, stack processor state: virtual PC, stack processor Process 2 program Thread 2 state: virtual PC, stack processor memory state: virtual memory PC, stack processor Thread m state: virtual Process n program PC, stack processor state: virtual memory PC, stack processor Process n Courtesy www.fmc-modeling.org Wednesday, December 5, 12
- 9. Multiprocessing • “The simultaneous execution of two or more programs by separate CPUs under integrated control.” • Clones the entire process, except resources • Copy-on-write memory Wednesday, December 5, 12
- 10. Forking Diagram courtesy cnx.org Wednesday, December 5, 12
- 11. Child Process • A cloned copy of a parent process • Receives a new process ID and a parent process ID • Does some work • Dies Wednesday, December 5, 12
- 12. ...sort of. Photo Credit: Christopher Brian (2011 Toronto Zombie Walk) Wednesday, December 5, 12
- 13. Parent Responsibilities • Reproduction • Monitors child process status • “Reap” zombie processes Wednesday, December 5, 12
- 14. Process Signals Signal Description SIGCHLD Child process died SIGINT User Interrupt SIGTERM Terminate SIGKILL Forcibly terminate Wednesday, December 5, 12
- 15.
- 16. Requirements • Unix-like operating system • PHP 4.1+ • PHP PCNTL extension (compile with --enable-pcntl) • PHP Semaphore extension, optional (--enable-sysvsem, --enable-sysvshm, --enable-sysvmsg) • Plenty of memory • Multiple CPU cores Wednesday, December 5, 12
- 17. Overview 1. Define signal handlers 2. Fetch a dataset 3. Fork off one child process for each item 4. Stop forking when a threshold is reached, and sleep 5. Reap a child process whenever SIGCHLD is received 6. If there’s more work to do, fork more processes 7. When all child processes have been reaped, terminate Wednesday, December 5, 12
- 18. declare(ticks = 1); // Setup our signal handlers pcntl_signal(SIGTERM, "signal_handler"); pcntl_signal(SIGINT, "signal_handler"); pcntl_signal(SIGCHLD, "signal_handler"); Wednesday, December 5, 12
- 19. function signal_handler($signal) { switch ($signal) { case SIGINT: case SIGTERM: // kill all child processes exit(0); case SIGCHLD: // reap a child process reap_child(); break; } } Wednesday, December 5, 12
- 20. $pid = pcntl_fork(); switch($pid) { case 0: // Child process call_user_func($callback, $data); posix_kill(posix_getppid(), SIGCHLD); exit; case -1: // Parent process, fork failed throw new Exception("Out of memory!"); default: // Parent process, fork succeeded $processes[$pid] = TRUE; } Wednesday, December 5, 12
- 21. Repeat for each unit of work Wednesday, December 5, 12
- 22. function reap_child() { // Check if any child process has terminated, // and if so remove it from memory $pid = pcntl_wait($status, WNOHANG); if ($pid < 0) { throw new Exception("Out of memory"); } elseif ($pid > 0) { unset($processes[$pid]); } } Wednesday, December 5, 12
- 23. Demo Time! http://gist.github.com/4212160 Wednesday, December 5, 12
- 24.
- 25. DON’T: • DON’T fork a web process (CLI only!) • DON’T overload your system • DON’T open resources before forking • DO respect common POSIX signals • DO remove zombie processes • DO force new database connections in children mysql_reconnect($s, $u, $p, TRUE); Wednesday, December 5, 12
- 26.
- 27. Race Conditions • A logic bug where the result is affected by the sequence or timing of uncontrollable events • Adding debug logic can change timing • Dirty reads • Lost data • Unpredictable behavior • Deadlocks, hanging, crashing Wednesday, December 5, 12
- 28.
- 29.
- 30. Solutions • Handle I/O in the parent process exclusively • Manage resources with semaphores and/or mutexes Wednesday, December 5, 12
- 31. Semaphores • Semaphore = atomically updated counter • Mutex = binary semaphore with ownership • PHP: sem_get(), sem_release() • Transactional databases use semaphores Wednesday, December 5, 12
- 32. Deadlocks Image credit: csunplugged.org Wednesday, December 5, 12
- 33.
- 34. Shared Memory • Advanced inter-process communication • Pass data back to the parent process • PHP Shared Memory extension (--enable-shmop) • PHP System V Shared Memory extension (--enable-sysvshm) • More robust • Compatible with other languages Wednesday, December 5, 12
- 35. Daemonization • Fork, kill parent • Orphaned child process continues running • Signal and error handling are critical • Server daemons usually fork child processes to handle requests Wednesday, December 5, 12
- 36.
- 37. Thank You! @compwright http://bit.ly/atlphpm Wednesday, December 5, 12