multi process php script to write csv file

multi_process_csv_task.php

<?php

class Task
{
    private $data = [];

    private $fp = null;

    private $columns = ['id', 'amount', 'date'];

    private $num = 10000;

    private $workerNum = 10;

    private $pageSize = 1;

    private $filename = '/tmp/data1.csv';

    private $counter = 0;

    public function __construct()
    {
        $this->generateData();

        $this->pageSize = $this->devideWork($this->num, $this->workerNum);

        @unlink($this->filename);
        $this->fp = fopen($this->filename, 'a+');
    }

    public function run()
    {
        fputcsv($this->fp, $this->columns);

        $this->runProcess();

        echo "total loop count is {$this->counter}\n"; // 0
    }

    private function runProcess()
    {
        for($i = 0; $i < $this->workerNum; $i++) {
            $pids[$i] = pcntl_fork();
            if (!$pids[$i]) {
                $this->writeCsv($i);
                exit($i);
            }
        }
        while (pcntl_waitpid(0, $status) != -1) {
            $status = pcntl_wexitstatus($status);
            echo "Child $status completed\n";
        }
    }

    private function writeCsv($page)
    {
        $start = $page * $this->pageSize;
        $stop = ($page+1)*$this->pageSize;
        echo "writing page {$page}, start={$start}, stop={$stop}, pageSize={$this->pageSize}\n";

        for ($i = $start; $i < $stop; $i++) {
            $row = $this->data[$i];
            fputcsv($this->fp, $row);

            $this->counter++;
        }
        echo "counter in child process is {$this->counter}\n"; // 1000
    }

    private function devideWork($total, $workNum)
    {
        return (int)($total/$workNum);
    }

    private function generateData()
    {
        for ($i = 0; $i < $this->num; $i++) {
            $amount = random_int($i, 10*$this->num);
            $date = date('Y-m-d H:i:s', 100 * $amount);
            $row = [$i, $amount, $date];

            $this->data[] = $row;
        }
    }


    public function __desctruct()
    {
        fclose($this->fp);
        unset($this->fp);
        unset($this->data);
    }
}

$task = new Task();
$task->run();
unset($task);