PHP线程不会结束

Question

I tried to implement multithreading in php to fetch data from a data source parallely.
But in the process, the threads i create to fetch the data continue to remain in the memory, even after the fetching.
This is the class that i call

class ClassName extends Thread {
    public function __construct($i){
        $this->i=$i;
    }
    public function run(){
        // functionCallToDataSource($this->i);
    }
}

and i call this class here (in a loop).

$workers = new ClassName(parameter);
$workers->start();
$workers->kill();       //this isnt working

This kill() doesnt seem to work for me, as the memory is not reduced after the functions have been performed. I have to restart my server to free the blocked memory