我已经尝试了两天了，但是没有成功。它只执行了一次，但是在初始加载后无法继续更新。函数不会自动更新。也不会在30秒后重新启动。代码对我来说似乎很好，但显然有一些知识差距，我有关于长轮询这是导致这不工作。如果有人有时间我'如果你能仔细检查一下，告诉我哪里做错了，我将不胜感激。任何帮助都是感激的，谢谢。
JavaScript/jQuery语言

function poll(pid){
    var dataString = 'pid=' + pid;
    $.ajax({type: 'GET', url: 'http://localhost:8888/mysite/execs/vote_count.php', data: dataString, async: true, cache: false, success: function(data){

 var post = $('#' +pid);
    var post_children = post.children();
    var upvotes = post_children.find('.upvotes');
    var downvotes = post_children.find('.downvotes');

downvotes.text("-" + data.downvotes);
upvotes.text("+" + data.upvotes);

    }, dataType: "json", complete: poll, timeout: 30000 });
};

$(".post").each(function(){
poll($(this).attr("id"));
});

PHP（搜索引擎）

<?php
$hostname = 'localhost';
$username = 'root';
$password = 'root';
$database = 'database';
try {
    $dbh = new PDO("mysql:host=$hostname;dbname=$database", $username, $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $stmt = $dbh->prepare("SELECT * FROM vote WHERE post = :pid AND rating = 'votedown'");
    $pid = $_GET['pid'];
    $stmt->bindParam(':pid', $pid, PDO::PARAM_STR);
    $stmt->execute();
    $result = $stmt->fetchAll();
    }
catch(PDOException $e)
    {
    echo $e->getMessage();
    }
    $stmt->execute();
    $downvotes = $stmt->rowCount();

    try {
    $dbh = new PDO("mysql:host=$hostname;dbname=$database", $username, $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $stmt = $dbh->prepare("SELECT * FROM vote WHERE post = :pid AND rating = 'voteup'");
    $pid = $_GET['pid'];
    $stmt->bindParam(':pid', $pid, PDO::PARAM_STR);
    $stmt->execute();
    $result = $stmt->fetchAll();
    }
catch(PDOException $e)
    {
    echo $e->getMessage();
    }
    $stmt->execute();
    $upvotes = $stmt->rowCount();
$arr = array("downvotes"=>$downvotes,"upvotes"=>$upvotes);
echo json_encode($arr);  
$dbh = null;
?>