带sleep（）的脚本正在减慢服务器速度，导致Apache崩溃

I have a website that has messaging functionality between users. When a user is logged in, I use jQuery.ajax() to call a PHP script to check for new messages. To cut down on requests, my PHP script loops a call to the check_new_messages() function and if there are no new messages, I call sleep(5) inside the loop, so that it waits 5 seconds and then continues the loop. I check how long the script has been executing by using microtime() and if it exceeds 60 seconds, I return 0. The ajax will receive this value and then call the script again.

function check_message_queue($user) {
    $response = 0;
    $msgs = 0;
    $time_start = microtime(true);

    while (!$msgs = check_new_messages($user)) {
        sleep(5);
        $time_end = microtime(true);
        if ($time_end - $time_start >= 60)
            return $response;
    }

    // has new messages
    sleep(5);
    return $response;
}

My php.ini has max_execution_time set to 120.

At first everything works OK, but when I refresh the page there is about a 10 second delay and sometimes I'll get the PHP error "Max execution time of 30 seconds has been exceeded" followed by Apache crashing. My PHP max_execution_time is definitely set to 120 seconds, so I'm not sure what's going on.

I've never done anything like this before, so hopefully it's just some bad coding on my part.

Here is my JavaScript:

var request_new_messages = function() {
    $.ajax({
        url: 'messages/checkqueue',
        type: 'post',
        contentType: 'application/x-www-form-urlencoded; charset=utf-8',
        data: { id: 0 },
        complete: function() { request_new_messages(); },
        error: function(jqXHR, textStatus, errorThrown) { handle_error(); },
        success:
            function(data, textStatus, jqXHR) {
                if (textStatus == "success") {
                    if (!isNaN(data)) {
                        var response = parseInt(data);
                        if (response > 0)
                            alert('You have ' + response + ' new messages.');
                    }
                }
            }
    });
};

You should not use PHP for that really. If you have an access to your server, i.e. it is not a share hosting or something like that, read about nodejs and socket.io. Besides that what is going on is that you are pausing the php every time once someone access it. Your script could be accessed several times per second. Imagine what will happen if you have 50 users. That could cause a crash of the apache. Can you please check the apache's logs and report the last few lines here (I mean before the crash).

Why keep it executing on the server?

PHP and JS are not the best technologies to use for this type of problem but if you must use them, the following approach would be better:

Make an AJAX request every 60 seconds (or any other suitable interval you wish to use), check once and return the results.

There are plenty of questions/answers on the best approach for messaging systems on here. Example from the 'related' tab on the right:

Best Way to Build a Web Based Instant Messaging?