I have a server to which multiple clients can connect to. The client is GUI while the server is command line. The client has several functions (such as connect and login) which, when sent to the server should receive a reply.
Basically I need to run the QTcpSocket functions waitForConnection and waitForReadyRead. However, I need to do this without blocking the UI.
What I thought of doing was the following:
Have a class (Client) implement QThread which does all the waiting. This is created in main.
Client::Client (...)
{
moveToThread (this); // Not too sure what this does
mClient = new QTcpSocket (this);
start();
}
void Client::run (void)
{
exec();
}
void Client::connectToServer (...)
{
mClient->connectToHost (hostname, port);
bool status = mClient->waitForConnected (TIMEOUT);
emit connected (status);
}
void Client::login (...)
{
... Similar to connectToServer ...
}
Then the GUI (for example, ConnectToServerDialog) I run this whenever I am ready to make a connection. I connect the "connected signal" from the thread to the dialog so when I am connected or connection timed out it will emit this signal.
QMetaObject::invokeMethod (mClient, "connectToServer", Qt::QueuedConnection,
Q_ARG (const QString &, hostname), Q_ARG (quint16, port));
I am getting an assert failure with this (Cannot send events to objects owned by a different thread.) Since I am fairly new to Qt I don't know if what I am doing is the correct thing.
Can somebody tell me if what I am doing is a good approach and if so why is my program crashing?
The best thing is never to call methods like waitForBlah() ... forcing the event loop to wait for an undetermined period introduces the possibility of the GUI freezing up during that time. Instead, connect your QTcpSocket's connected() signal to some slot that will update your GUI as appropriate, and let the event loop continue as usual. Do your on-connected stuff inside that slot.
I don't recommend start thread in constructor.
Initialize it like:
Client * client = new Client();
client->moveToThread(client);
client->start();
Or if you don't want to use such solution, add in constructor before start(); line this->moveToThread(this);
upd: sorry, i didn't saw at first time, that you have this string.
Related
I'm trying to develop an API for multiplayer online using socket programming in node js
I have some basic questions:
1. How to know which connection is related to a user?
2. How to create a socket object related to another person?
3. When it's opponent turn, how to make an event?
4. There is a limited time for move, how to handle the time to create an event and change turn?
As it is obvious I don't know how to handle users and for example list online users
If you can suggest some articles or answering these questions would be greate
Thanks
Keep some sort of data structure in memory where you are saving your sockets to. You may want to wrap the node.js socket in your own object which contains an id property. Then you can save these objects into a data structure saved in memory.
class User {
constructor(socket) {
this.socket = socket;
this.id = //some random id or even counter?
}
}
Then save this object in memory when you get a new socket.
const sockets = {}
server = net.createServer((socket) => {
const user = new User(socket);
sockets[user.id] = user
})
I am unsure what you mean by that, but maybe the above point helps out
This depends on when you define a new turn starts. Does the new turn start by something that is triggered by another user? If so use your solution to point 2 to relay that message to the related user and write something back to that socket.
Use a timeout. Maybe give your User class an additional property timeout whenver you want to start a new timeout do timeout = setTimeout(timeouthandler,howlong) If the timeouthandler is triggered the user is out of time, so write to the socket. Don't forget to cancel your timeouts if you need to.
Also, as a side note, if you are doing this with pure node.js tcp sockets you need to come up with some ad-hoc protocol. Here is why:
socket.on("data", (data) => {
//this could be triggered multiple times for a single socket.write() due to the streaming nature of tcp
})
You could do something like
class User {
constructor(socket) {
this.socket = socket;
this.id = //some random id or even counter?
socket.on("data", (data) => {
//on each message you get, find out the type of message
//which could be anything you define. Is it a login?
// End of turn?
// logout?
})
}
}
EDIT: This is not something that scales well. This is just to give you an idea on what can be done. Imagine for some reason you decide to have one node.js server instance running for hundreds of users. All those users socket instances would be stored in the servers memory
i use web sockets and the onclose method does not get triggert when the server is down.
i tried to close the ws connections manually with progress.exit but it seems this only gets triggert on a clean exit.
is their a way to catch a stopped nodejs app and execute code before the stop?
it should trigger on ctr+c and any other crash/exit.
basicly i want to tell the client when the connection is not alive anymore before he is trying to do something, since onclose does not handel every case, what can i do to check the connection?
the only solution i came up with is to ping the server from time to time.
since this is not possible i started sending pings as a workarround:
var pingAnswer = true;
pingInterval = setInterval(function(){
if(pingAnswer){
ws.send(JSON.stringify({type:'ping'})); //on the serverside i just send a ping back everytime i recive one.
pingAnswer = false;
}else{
clearInterval(pingInterval);
//reload page or something
}
},1000);
ws.onMessage(function(e){
m = JSON.parse(e.data);
switch(m.type){
....
case 'ping':
pingAnswer=true;
return;
}
}
);
You don't provide a snippet showing how you're defining your on('close',...) handler, but it's possible that you're defining the handler incorrectly.
At the time of this writing, the documentation for websocket.onclose led me to first implement the handler as ws_connection.onclose( () => {...});, but I've found the proper way to be ws_connection.on('close', () => {...} );
Maybe the style used in the ws documentation is some kind of idiom I'm unfamiliar with.
I've tested this with node 6.2.1 and ws 1.1.1. The on.('close',...) callback is triggered on either side (server/client) when the corresponding side is shutdown via Ctrl+c or crashes for whatever reason (for example, for testing, JSON.parse("fail"); or throw new Error('');).
I have already written a request-method in java that sends a request to a simple Server. I have written this simple server and the Connection is based on sockets. When the server has the answer for the request, it will send it automatically to client. Now I want to write a new method that can behave as following:
if the server does not answer after a fixed period of time, then I send a new Request to the server using my request-method
My problem is to implement this idea. I am thinking in launching a thread, whenever the request-method is executed. If this thread does not hear something for fixed period of time, then the request method should be executed again. But how can I hear from the same socket used between that client and server?
I am also asking,if there is a simpler method that does not use threads
curently I am working on this idea
I am working on this idea:
1)send a request using my request-method
2)launch a thread for hearing from socket
3)If(no answer){ go to (1)}
else{
exit
}
I have some difficulties in step 3. How I can go to (1)
You may be able to accomplish this with a single thread using a SocketChannel and a Selector, see also these tutorials on SocketChannel and Selector. The gist of it is that you'll use long-polling on the Selector to let you know when your SocketChannel(s) are ready to read/write/etc using Selector#select(long timeout). (SocketChannel supports non-blocking, but from your problem description it sounds like things would be simpler using blocking)
SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress("http://jenkov.com", 80));
Selector selector = Selector.open();
SelectionKey key = socketChannel.register(selector, SelectionKey.OP_READ);
// returns the number of channels ready after 5000ms; if you have
// multiple channels attached to the selector then you may prefer
// to iterate through the SelectionKeys
if(selector.select(5000) > 0) {
SocketChannel keyedChannel = (SocketChannel)key.channel();
// read/write the SocketChannel
} else {
// I think your best bet here is to close and reopen the Socket
// or to reinstantiate a new socket - depends on your Request method
}
I am working on this idea:
1)send a request using my request-method
2)launch a thread for hearing from socket
3)If(no answer) then go to (1)
In my project I have created some network calls to the servlets in separate Thread where before that thread starts I show a spinner as wait progress. Until that network Thread finishes the waitprogress is displayed on to the screen and when I receive response from the server I have to explicitly call progress bar's dispose() method to dispose that progress bar. So, This is bit complicated whenever I make calls establishing GPRS connection while network strength goes down there I found sometimes it takes about 2-3 minutes to throw an IO Exception or receive response from server where I dispose waitprogress, show error message and proceed. I dont add any cancel command to waitprogress as network calls are made using separate thread so disposing waitprogress will allow user to make another call where the user is needed to wait until he gets response.
The above scenario is complicated because the user will not be waiting for this long to get response. There must be some way that whenever I call network Thread and show progress bar the user should be able to cancel all the operations including network thread, go back to previous state and make another call if there is no or poor connectivity.
Here, I am using Lwuit.
In NetworkManager class you can add this function and actived at from your class
only if lwuit is at open code in your application , you can add this function:
public void killAll() {
for (int i = 0; i < pending.size(); i++) {
((ConnectionRequest) pending.elementAt(i)).kill();
}
pending.removeAllElements();
for (int i = 0; i < networkThreads.length; i++) {
networkThreads[i].currentRequest.kill();
}
}
after or before this you need call dispose() method.
I need to develop a netty based Client, that accepts messages from a Notification Server, and places these messages as Http Requests to another Server in real time.
I have already coded a working application which does this, but I need to add multi-threading to this.
At this point, I am getting confused on how to handle Netty Channels inside a multi-threaded program, as I am all loaded with the conventional approach of sockets and threads.
When I tried to separate the Netty requesting part into a method, It complains about the Channels not being closed.
Can anyone guide me how to handle this?
I would like to use ExecutionHandler and OrderedMemoryAwareThreadPoolExecutor, but I am really new into this.
Help with some examples would be a real favour at this time.
Thanks in advance.
Just add an ExecutionHandler to the ChannelPipeline. This will make sure that every ChannelUpstreamHandler which is added behind the ExecutionHandler will get executed in an extra thread and so does not block the worker-thread.
Have you looked at the example code on the Netty site? The TelnetServer looks to do what you are talking about. The factory creates new handlers whenever it gets a connection. Threads from the Executors will be used whenever there is a new connection. You could use any thread pool and executor there I suspect:
// Configure the server.
ServerBootstrap bootstrap = new ServerBootstrap(
new NioServerSocketChannelFactory(
Executors.newCachedThreadPool(), << change
Executors.newCachedThreadPool())); << change
// Configure the pipeline factory.
bootstrap.setPipelineFactory(new TelnetServerPipelineFactory());
// Bind and start to accept incoming connections.
bootstrap.bind(new InetSocketAddress(8080));
The TelnetServerHandler then handles the individual results.
#Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
// Cast to a String first.
// We know it is a String because we put some codec in TelnetPipelineFactory.
String request = (String) e.getMessage();
// Generate and write a response.
String response;
boolean close = false;
if (request.length() == 0) {
response = "Please type something.\r\n";
When the telnet is ready to close the connection it does this:
ChannelFuture future = e.getChannel().write(response);
if (close) {
future.addListener(ChannelFutureListener.CLOSE);
}