php中popen之后一直等待脚本执行完毕才向下执行，如何解决？

<code>//test.php
pclose(popen('php '.__DIR__.'/index.php','r'));
$fp = fopen('product.txt', 'cb');
if(flock($fp, LOCK_EX | LOCK_NB)){
    echo "ok<br>";
}else{
    echo "no<br>";
}
fclose($fp);

</code>

<code>//index.php
sleep(10);
set_time_limit(0);
$fp = fopen('product.txt', 'cb');
flock($fp, LOCK_EX | LOCK_NB);
for($i = 10 ; $i ;$i--){
    fwrite($fp,$i."\n");
    sleep(6);
}
fclose($fp);</code>

<code>//test.php
pclose(popen('php '.__DIR__.'/index.php','r'));
$fp = fopen('product.txt', 'cb');
if(flock($fp, LOCK_EX | LOCK_NB)){
    echo "ok<br>";
}else{
    echo "no<br>";
}
fclose($fp);

</code>

<code>//index.php
sleep(10);
set_time_limit(0);
$fp = fopen('product.txt', 'cb');
flock($fp, LOCK_EX | LOCK_NB);
for($i = 10 ; $i ;$i--){
    fwrite($fp,$i."\n");
    sleep(6);
}
fclose($fp);</code>