第一次连接后TCP服务器没有响应

Question

我有一个TCP服务器，它侦听传入的消息（数据/请求）并相应地回复。但是，它在第​​一次连接后没有回复。如果是数据消息，则将数据插入数据库，但确认消息不会到达客户端。并且，如果它是数据请求消息则没有响应。当我重新启动服务器时，它只能正确回复第一个传入连接。从此以后，服务器到客户端都没有响应。 我附上了我的代码，请建议可以采取哪些措施来解决问题。     

    /**
     * Settings
     */

    $listen_address         = "0.0.0.0";
    $listen_port            = ****;

    $mysql_server           = "localhost";
    $mysql_username         = "root";
    $mysql_password         = "*****";
    $mysql_database         = "*****";

    /**
     * End Settings
     */

    function socketError($errorFunction, $die=false) {
            $errMsg = socket_strerror(socket_last_error());

            echo("{$errorFunction}() error: $errMsg");

            if ($die) {
                    exit();
            }
    }

function doQuery($query) {
    global $db, $mysql_server, $mysql_username, $mysql_password, $mysql_database, $thread_id;
    if (0) echo "Trying query: $query\n";
    if(!($res = mysqli_query($db, $query))) {
        @mysqli_kill($db, $thread_id);
        @mysqli_close($db);
        $db = mysqli_connect($mysql_server, $mysql_username, $mysql_password, $mysql_database);
            if(mysqli_connect_errno()) {
                    echo("\r\nFailed to connect to MySQL: " . mysqli_connect_error());
            }
        if(!($res = mysqli_query($db, $query))) {
                    echo("Error: " . mysqli_error($db) . "\n");
        }
            }
    return $res;
}

    function logMessage($socket, $msg) {
            global $db, $mysql_server, $mysql_username, $mysql_password, $mysql_database, $thread_id;
            $get_ip = socket_getpeername($socket, $address);
            echo("Received ({$address}): {$msg}\n");

    // process update:<pid>:<sid>! request
    // the response is sent in format: d_id:value<uptill the first comma>,
    // in case of multiple rows, they are separated by LF character (\n)
    if (preg_match('/^update:([0-9]+):([0-9]+)!/', $msg, $matches)) {
        $pid = $matches[1];
        $sid = $matches[2];
        $res = doQuery("SELECT d_id FROM devices WHERE project_id = $pid AND subproject_id = $sid");
        if ($res) {
            if (mysqli_num_rows($res) > 0) {
                $output = '';
                $i = 0;
                while ($r = mysqli_fetch_array($res)) {
                    $res2 = doQuery("SELECT tt.d_id, tt.field_a, tt.value FROM data tt INNER JOIN (SELECT d_id, MAX(update_time) AS MaxDateTime FROM data WHERE d_id = {$r['d_id']} GROUP BY d_id) groupedtt ON tt.d_id = groupedtt.d_id AND tt.update_time = groupedtt.MaxDateTime");
                    if ($res2) {
                        if (mysqli_num_rows($res2) > 0) {
                            while ($r2 = mysqli_fetch_array($res2)) {
                                $tmp = explode(',', $r2['value'], 2);
                                $output .= ($i>0?"\n":'').$r2['d_id'].':'.$r2['field_a'].':'.$tmp[0].',';
                                ++$i;
                            }
                        }
                    }
                }
                return $output;
           }
        }
    }
    else {
            // Ensure nothing breaks our query
            $msg = str_replace("'", "\'", $msg);

        $parts = explode(':', $msg);

        if (is_numeric($parts[0])) {
                    //if(!mysqli_query($db, "INSERT INTO data (data, datetime, receiver) VALUES ('{$msg}', '".time()."', '".$address."')")) {
 doQuery("INSERT INTO data (sender, d_id, value, update_time, field_a) VALUES ('".$address."', {$parts[0]}, '{$parts[2]}', '".date("Y-m-d H:i:s")."','{$parts[1]}')");
            return "yes\n";
        }
        else return "no\n";
    }
    }

    function sendData($socket, $message) {
            socket_write($socket, $message);
    }

    error_reporting(E_ALL);
    set_time_limit(0);
    ob_implicit_flush();
    ignore_user_abort(true);

    // Stage 1: MySQL Connection
    $db = mysqli_connect($mysql_server, $mysql_username, $mysql_password, $mysql_database);

    if(mysqli_connect_errno()) {
            echo("\r\nFailed to connect to MySQL: " . mysqli_connect_error());
    }
else
    $thread_id = mysqli_thread_id($db);

    // Stage 2: start listening

    if(!($server = @socket_create(AF_INET, SOCK_STREAM, SOL_TCP))) {
            socketError("socket_create", true);
    }

    socket_set_option($server, SOL_SOCKET, SO_REUSEADDR, 1);

    if(!@socket_bind($server, $listen_address, $listen_port)) {
            socketError("socket_bind", true);
    }

    if(!@socket_listen($server)) {
            socketError("socket_listen", true);
    }

    $allSockets = array($server);

    echo("Listening on port {$listen_port}\n");

    // Stage 3: accept clients

    while (true) {
            if(connection_aborted()) {
                    foreach($allSockets as $socket) {
                            socket_close($socket);
                    }

                    break;
            }

            $changedSockets = $allSockets;
            @socket_select($changedSockets, $write = NULL, $except = NULL, 5);

            foreach($changedSockets as $socket) {

                    if ($socket == $server) {
                            if(!($client = @socket_accept($server))) {
                                    socketError("socket_accept", false);
                            } else {
                                    $allSockets[] = $client;
                            }
                    } else {
                            $data = socket_read($socket, 2048);

                            if ($data === false || $data === '') {
                    unset($allSockets[array_search($socket, $allSockets)]);
                                    socket_close($socket);
                            } else {
                                    if(trim($data != "")) {
                                            $response = logMessage($socket, $data);
                                            sendData($socket, $response);
                                    }
                            }
                    }
            }
    }

?>