NIO+Multithreaded TCPSocket listener, very low cpu utilisation

Wed Nov 15 11:13:52 UTC 2017

So thanks for the suggestions,  i have fixed HTTP response not 
postman cal also parse the headers correctly!! happy days.

I have removed the duration from the Socket.select but the 
application seems to process a bunch or requests and then it 
stalls for several seconds (3/5) and then it resumes.

The httpclinet which i'm using to test the application is 
reporting: "connection timeout".

Could this be caused by the GC?

```updated code
import std.algorithm : remove;
import std.conv : to;
import core.thread: Thread;
import std.socket : InternetAddress, Socket, SocketException, 
SocketSet, TcpSocket, SocketShutdown;
import core.time : Duration, dur;
import std.stdio : writeln, writefln;
import std.parallelism : task, TaskPool;

string to_retlf (string s)
{
    import std.algorithm;
    import std.string;
    return s
       .lineSplitter
       .map!(a => chomp (a))
       .join ("\r\n");
}

void main(string[] args)
{
     ushort port;

     if (args.length >= 2)
         port = to!ushort(args[1]);
     else
         port = 4444;

     auto listener = new TcpSocket();
     assert(listener.isAlive);
     listener.blocking = false;
     listener.bind(new InternetAddress(port));
     listener.listen(100);
     writefln("Listening on port %d.", port);

     auto taskPool = new TaskPool(8);

     string response = "HTTP/1.1 200 OK
Server: dland:v2.076.1
Date: Tue, 11 Nov 2017 15:56:02 GMT
Content-Type: text/html; charset=UTF-8
Content-Length: 51

<html><head></head><body>Hello World!</body></html>".to_retlf;

     new Thread({
         auto listeningSet = new SocketSet();
         while(true) {
             listeningSet.add(listener);
             if (Socket.select(listeningSet, null, null)) {
                 if (listeningSet.isSet(listener))        // 
connection request
                 {
                     Socket socket = listener.accept();
                     assert(socket.isAlive);
                     //writefln("Connection from %s established.", 
socket.remoteAddress().toString());
                     auto task = task!handle_socket(socket, 
response);
                     taskPool.put(task);
                 }
             }
             listeningSet.reset();
         }
     }).start();
}

void handle_socket(Socket socket, string response) {
     auto socketSet = new SocketSet();
     while(true) {
         socketSet.add(socket);
         if (Socket.select(socketSet, null, null)) {
             char[1024] buf;
             auto datLength = socket.receive(buf[]);

             if (datLength == Socket.ERROR)
                 writeln("Connection error.");
             else if (datLength != 0)
             {
                 //writefln("Received %d bytes from %s: \"%s\"", 
datLength, socket.remoteAddress().toString(), buf[0..datLength]);
                 //writefln("Writing response");
                 socket.send(response);
             }
             // release socket resources now

             socket.close();

             break;

         }
         socketSet.reset();
     }
```

Regards