两个同时的 AJAX 请求不会并行运行 [英] Two simultaneous AJAX requests won't run in parallel

问题描述

我有两个同时运行的 AJAX 请求的问题.我有一个将数据导出到 XSLX 的 PHP 脚本.这个操作需要很多时间，所以我试图向用户展示进度.我正在使用 AJAX 和数据库方法.实际上，我很确定它曾经可以工作，但我不知道为什么，它不再在任何浏览器中工作.新浏览器有什么变化吗?

I have problem with two simultaneous AJAX requests running. I have a PHP script which is exporting data to XSLX. This operation take a lot of time, so I'm trying to show progress to the user. I'm using AJAX and database approach. Actually, I'm pretty sure it used to work but I can't figure out why, it's no longer working in any browser. Did something change in new browsers?

$(document).ready(function() {

        $("#progressbar").progressbar();

        $.ajax({
            type: "POST",
            url: "{$BASE_URL}/export/project/ajaxExport",
            data: "type={$type}&progressUid={$progressUid}" // unique ID I'm using to track progress from database
        }).done(function(data) {
            $("#progressbar-box").hide();
            clearInterval(progressInterval);
        });

        progressInterval = setInterval(function() {
            $.ajax({
                type: "POST",
                url: "{$BASE_URL}/ajax/progressShow",
                data: "statusId={$progressUid}" // the same uinque ID
            }).done(function(data) {
                data = jQuery.parseJSON(data);
                $("#progressbar").progressbar({ value: parseInt(data.progress) });
                if (data.title) { $("#progressbar-title").text(data.title); }
            });
        }, 500);

    });

• 进度在数据库中正确更新
• JS 计时器正在尝试获取进度，我可以在控制台中看到它，但是所有这些请求都在加载第一个脚本的整个持续时间，脚本一结束，就会加载这些 ajax 进度调用

那么，为什么第二个 AJAX 调用要等待第一个调用完成?

So, why is the second AJAX call waiting for the first one to finish?

推荐答案

听起来像是会话阻塞问题

Sounds like a session blocking issue

默认情况下，PHP 将其会话数据写入文件.当您使用 session_start() 启动会话时，它会打开文件进行写入并锁定它以防止并发编辑.这意味着对于使用会话通过 PHP 脚本的每个请求都必须等待第一个会话完成该文件.

By default PHP writes its session data to a file. When you initiate a session with session_start() it opens the file for writing and locks it to prevent concurrent edits. That means that for each request going through a PHP script using a session has to wait for the first session to be done with the file.

解决此问题的方法是将 PHP 会话更改为不使用文件或关闭会话，如下所示:

The way to fix this is to change PHP sessions to not use files or to close your session write like so:

<?php
    session_start(); // starting the session

    $_SESSION['foo'] = 'bar'; // Write data to the session if you want to

    session_write_close(); // close the session file and release the lock

    echo $_SESSION['foo']; // You can still read from the session.

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