Run PHP with multithreading (tesseract)

Question

I need to send some images through tesseract, and to save time I want to run tesseract in parallel with up to 6 instances.

I have looked at this question, but cant really figure out how to write the code

How can one use multi threading in PHP applications

All images are fetched from a database, and the results are written back to the specific row in the database together with the rest of the information related to the image

Could anyone link to an example or could anyone write a quick example on how to do the job?

When a process is completed a new one must be started so there will always be up to 6 processes running at the same time?

update

class Command {
    private $descriptorspec;
    
    private $output = '';
    
    public function __construct(){
        $this->descriptorspec = [
            0 => ['pipe', 'r'], // stdin
            1 => ['pipe', 'w'], // stdout
            2 => ['pipe', 'w'], // stderr
        ];
    }
    
    public function output(): string{
        return $this->output;
    }
    
    public function exec(string $syntax): string{
        $process = proc_open($syntax, $this->descriptorspec, $pipes);
        
        $this->output = stream_get_contents($pipes[1]);
        fclose($pipes[1]);
        
        $stderr = stream_get_contents($pipes[2]);
        fclose($pipes[2]);
        
        proc_close($process);
        
        return $stderr;
    }
}

$Cmd = new Command;
$Cmd->exec('tesseract ...');

Answer 1

don't do it. PHP has really shitty support for multithreading. instead, use multi processing. use proc_open & co. -- http://php.net/manual/en/function.proc-open.php

Answer 2

You do not need to use multi-threading. To run the 6 workers, without the need to sync with parent proccess - you can use proc_open

Multithreading is faster, takes up less resources (there is no separate namespace for it), and you can run them 4 times more than the forks, but multithreading requires build PHP with non-ZTS (some extensions do not work with non-ZTS), and requires something you would understand pthread model.

For exampe:

We create 6 worker with proc_open, and Base process listen to die childs (i am use my wrapper, work with Ev li or Event lib or Without their) (child-processes), maybe you like wrapper reactphp (child-processes)

    $child = new ChildProcesses();
    $child->add('<system command>');
    $child->add('<system command>');
    $child->add('<system command>');
    $child->add('<system command>');
    $child->add('<system command>');
    $fails = $child->check(null, function(ChildProcess $process) {
        echo 'Error with chld process';
    });

Or use pthread read official documentatin. Your need recompile PHP in non-ZTS, and install pthread extension. For your problem, I would use Pool

You need look at the first example in this page Pool pthreads

Update:

If you need have all time - six workers. You need create six listeners. And communication between processes use zmq or rabbitmq, gearman or other different queue. Your processes will never die, and the fallen lifted by supervisord.

For example:

$loop = Factory::create();
$context = new Context($loop));
$context->getSocket(\ZMQ::SOCKET_SUB);
$context->connect($host);
$context->subscribe('you_queue');
$context->on('messages', function($messages){
    // get specific data and run operation
});
$loop->run();

Be careful, zmq is not quite queue.

1. It does not save messages
2. react / zmq uses EventLib, so actually my example will be asynchronous.

You need use Gearman or RabbitMQ - there have ideal functionality to your task

---

Regards Maxim

Answer 3

I wrote an example (base on child-processes). This should solve your problem:

This is parent.php:

$child = new ChildProcesses();
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w1'));
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w2'));
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w3'));
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w4'));
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w5'));
$child->addProcessInstance(new \TkachInc\ChildProcesses\ChildProcess('php worker.php -w6'));
$child->daemon();

And your worker.php (i added example output, you need delete it):

$options = getopt("w:");
if(isset($options['w']))
{
    echo $options['w'].PHP_EOL;

    switch ($options['w'])
    {
        case "1":
            sleep(5);
            break;
        case "2":
            sleep(5);
            break;
        case "3":
            sleep(7);
            break;
        case "4":
            sleep(5);
            break;
        case "5":
            sleep(7);
            break;
        case "6":
            sleep(5);
            break;
    }
}

// your logic to receive from database and write to database

---

Regards Maxim