Why does chrome not establish the connection directly after the dns lookup? - c++

Question

I have the problem that Chrome is waiting for something after the DNS lookup before establishing the connection.
My problem -> (https://imgur.com/qA5ADOa)
On the picture you can see that after the dns lookup there is a big gap and the request took 313ms although all values together are maximum 16ms.
Apache on this picture -> (https://imgur.com/UI4ToDu).
What does apache do that problem does not occur? On this picture you can see very well that problem does not occur at apache.
I am writing a simple web server in C++ just for practice. I test the webserver with the Chrome Browser. The code is very simple and without errorhandling, here the part after the socket creation with hard coded response:
std::memset(&myAddr, 0, sizeof(myAddr));
myAddr.sin_family = AF_INET;
myAddr.sin_addr.s_addr = INADDR_ANY;
myAddr.sin_port = htons(80);
bind(acceptSock, (sockaddr *)&myAddr, sizeof(myAddr));
listen(acceptSock, 5);
clientSock = accept(acceptSock, (sockaddr *)&clientAddr, &clientAddrLen);
std::vector<char> recvbuf(BUFFER_LENTH);
recv(clientSock, &recvbuf[0], recvbuf.size(), 0);
std::ifstream file("index.html");
if (file.is_open()) {
std::string content;
std::string buf;
while (std::getline(file, buf)) {
content += buf;
buf.clear();
}
file.close();
size_t contentLength = content.size();
std::string sendbuf = "HTTP/1.1 200 OK\r\n";
sendbuf += "Content-Type: text/html; charset=UTF-8\r\n";
sendbuf += "Content-Length: " + std::to_string(contentLength) + "\r\n";
sendbuf += "Server: meinWebServer\r\n";
sendbuf += "\r\n";
sendbuf += content;
send(clientSock, sendbuf.c_str(), sendbuf.size(), 0);
}
What can I do to prevent this problem?
Why and what is Chrome waiting for after the lookup?