I've a class which is responsible for listening two other machines which have exactly the same classes, so it's a network of three computers having the same code. The connection is there and I can see them passing data to each other. Everything until there works OK.
Things get tricky when I take out one of the machines and observe how the other two behave. Expectedly, when one of the machines stops working for some reason, other two should continue. And if two of them stop, the remaining should go on.
I tried to implement this mechanism below. However, when I take out one of the machines, the program keeps waiting, so it does not switch to "two-way comparison mode".
public void listen() {
try {
logger.info("Creating listener sockets");
while (isRunning) {
final byte[] buf = new byte[bufferSize];
final DatagramPacket packetOne = new DatagramPacket(buf, buf.length);
final DatagramPacket packetTwo = new DatagramPacket(buf, buf.length);
MediatorMessageMsg mediatorMessageOne = null;
MediatorMessageMsg mediatorMessageTwo = null;
try {
socketReceiverOne.receive(packetOne);
ByteArrayInputStream firstInput = new ByteArrayInputStream(buf);
mediatorMessageOne = MediatorMessageMsg.parseDelimitedFrom(firstInput);
socketReceiverTwo.receive(packetTwo);
ByteArrayInputStream secondInput = new ByteArrayInputStream(buf);
mediatorMessageTwo = MediatorMessageMsg.parseDelimitedFrom(secondInput);
logger.trace("Received packets");
} catch (final SocketTimeoutException e) {
logger.trace(e.getMessage());
continue;
} catch (final SocketException e) {
logger.warn(e);
logger.warn("Ignore the error and go on.");
continue;
} catch (final IOException e) {
logger.error("Incoming communication stopped!");
logger.error(e);
stop();
}
// if two mediators sent the data, it's OK
if (packetOne.getLength() > 0 && packetTwo.getLength() > 0) {
handlePackets(mediatorMessageOne, mediatorMessageTwo);
logger.info("Number of active mediators: 2. Comparison style: 1v1v1");
}
// if only one sent the data, compare it with our own
else if (packetOne.getLength() > 0 || packetTwo.getLength() > 0) {
// whicehever sent the data, compare its data with our own
logger.info("Number of active mediators: 1. Comparison style: 1v1");
if (packetOne.getLength() > 0) {
handlePackets(mediatorMessageOne);
} else {
handlePackets(mediatorMessageTwo);
}
}
// if no data is sent, then pass our own directly
else {
logger.info("Number of active mediators: 0. Comparison style: No Comparison");
// our datamodel to retrieve data on our own
DataModel modelOwn = DataModel.getInstance();
MediatorMessageMsg newMessage = MediatorMessageMsg.newBuilder().setHeading(modelOwn.getHeading()).setSpeed(modelOwn.getSpeed()).setSender(getId()).build();
// publish(topicName, newMessage);
}
Thread.sleep(1);
}
socketReceiverOne.close();
socketReceiverTwo.close();
logger.info("stopped");
} catch (final IllegalArgumentException e) {
logger.error("Illegal argument received: " + e);
} catch (final Exception e) {
logger.error("Unexpected error occured: " + e);
} finally {
if (socketReceiverOne instanceof DatagramSocket && socketReceiverTwo instanceof DatagramSocket) {
if (!socketReceiverOne.isClosed() || !socketReceiverTwo.isClosed()) {
socketReceiverOne.close();
socketReceiverTwo.close();
}
}
}
}
To save your time, let me share my opinion on the matter. I suspect the problem to be in this part:
socketReceiverOne.receive(packetOne);
ByteArrayInputStream firstInput = new ByteArrayInputStream(buf);
mediatorMessageOne = MediatorMessageMsg.parseDelimitedFrom(firstInput);
socketReceiverTwo.receive(packetTwo);
ByteArrayInputStream secondInput = new ByteArrayInputStream(buf);
mediatorMessageTwo = MediatorMessageMsg.parseDelimitedFrom(secondInput);
To me it seems like the program expects a package and when it cannot receive it, it keeps waiting. Although I have time out exception condition, I cannot get this done.
private int socketTimeout = 1000 * 2;// 2sec
socketReceiverOne.setSoTimeout(socketTimeout);
socketReceiverTwo.setSoTimeout(socketTimeout);
Any thoughts?
Okay I found where I was mistaken. I needed more ports (for in and out). Once I incorporated those ports, the problem did not occur again.
Related
I have a problem with my Java socket and connection. It seems like my input stream does not read any data even though there is data on the stream. Here is an example on how we read data:
InputStream is = socket.getInputStream();
StringBuffer buf = new StringBuffer();
final int SO_TIME = 2500;
socket.setSoTimeout(SO_TIME);
long readTime = 0;
boolean remoteSocketClosed = false;
//Read data while the Remote-Socket is opened and the timeout is OK
while (!remoteSocketClosed && readTime < 30000)
{
try
{
int c = is.read();
if (c != -1)
{
buf.append((char)c);
}
else //c==-1
{
remoteSocketClosed = true;
}
}
catch (SocketTimeoutException socketTimeout)
{
readTime += SO_TIME;
}
}
if (readTime >= 30000)
{
throw new IOException("No answer from server after request (" + readTime +"ms )");
}
else
{
if (buf.length() > 0)
{
return buf;
}
else
{
return null;
}
}
finally
{
try
{
if (socket!=null)
socket.close();
}
catch (Exception e)
{
l.error("Socket not closed", e);
}
try{Thread.sleep(250);}catch(Exception e){}
}
Now this looks fine to me. However when there is data on the stream, it will not get picked up. I can use telnet and see that data is coming in on that connection, yet Java just throws the IOException (timeout).
The server is running on the same machine (localhost), and we can send data to the server, yet the answer is lost somehow (only in Java not in telnet). Is this some weird setting I don't know about? We are using Windows 10 and Java 8, firewalls are all disabled. I have never experienced something like this so any help is appreciated.
Sometimes you just don't see the forest for the trees and have to sleep over it...
The problem is my condition
if (c != -1)
{
buf.append((char)c);
}
else //c==-1
{
remoteSocketClosed = true;
}
But the server never closes the connection... So I never exit my loop and im stuck for 30 seconds running into socket timeouts. After the 30 seconds of waiting my answer is in the StringBuffer but of course my readTime is 30000 so I throw the exception rather providing an answer... I will have to think of an EndOfPackage Byte or something to avoid this.
Thanks for any help tho
In my application, I have used two while loops for reading the sockets. while loop-1 takes 1% of CPU and while loop-2 takes 100% CPU. I am confused. Please share your valuable thoughts. For more information, I have added two while loops below:
While loop-1:
while(true) {
String message = onReadFinal(in);
if (message != null) {
synchronized (message) {
System.out.println("Message size:" + message);
}
}
}
private String onReadFinal(DataInputStream in) {
String mess = null;
try{
StringBuilder builder = new StringBuilder();
do {
builder.append(in.readInt());
} while(in.available() > 0);
mess = builder.toString();
} catch(IOException e){ e.printStackTrace(); }
return mess;
}
While loop-2:
while(true) {
String message = onRead(in);
if (message != null) {
synchronized (message) {
System.out.println("Message size:" + message);
}
}
}
public String onRead(DataInputStream input) {
String socketmessage = null;
int length;
try {
if(input != null) {
length = input.available();
if(length>0) {
byte[] message = new byte[length];
input.readFully(message, 0, message.length);
socketmessage = new String(message);
}
}
} catch (IOException ioException) {
ioException.printStackTrace();
}
return socketmessage;
}
Also, if I execute infinite while loop with no statements, it takes 100% of CPU. Someone can you please explain.
if a loop does not contain blocking operations, it always would take 100% CPU.
Your first loop contains blocking operation in.readInt(). Your second loop also contains potentially blocking operation input.readFully(), but calls it only when the stream buffer has enough bytes to read, and so in fact this operation does not block. When there is not enough bytes, the loop immediately repeats non-blocking operation input.available(), without much sense.
You better tell us what you want.
So I am writing my own piece of stuff using jzmq GIT master branch and ZeroMQ 3.2.3.
After installation I tried to test the following simple PUB/SUB program, where a publisher and a subscriber talk in a single process. Since the test is under Windows, I used TCP.
public class ZMQReadynessTest {
private ZMQ.Context context;
#Before
public void setUp() {
context = ZMQ.context(1);
}
#Test
public void testSimpleMessage() {
String topic = "tcp://127.0.0.1:31216";
final AtomicInteger counter = new AtomicInteger();
// _____________________________________ create a simple subscriber
final ZMQ.Socket subscribeSocket = context.socket(ZMQ.SUB);
subscribeSocket.connect(topic);
subscribeSocket.subscribe("TestTopic".getBytes());
Thread subThread = new Thread() {
#Override
public void run() {
while (true) {
String value = null;
// This would result in trouble /\/\/\/\/\/\/\/\/\
{
ByteBuffer buffer = ByteBuffer.allocateDirect(100);
if (subscribeSocket.recvZeroCopy( buffer,
buffer.remaining(),
ZMQ.DONTWAIT
) > 0 ) {
buffer.flip();
value = buffer.asCharBuffer().toString();
System.out.println(buffer.asCharBuffer().toString());
}
}
// This works perfectly + + + + + + + + + + + + +
/*
{
byte[] bytes = subscribeSocket.recv(ZMQ.DONTWAIT);
if (bytes == null || bytes.length == 0) {
continue;
}
value = new String(bytes);
}
*/
if (value != null && value.length() > 0) {
counter.incrementAndGet();
System.out.println(value);
break;
}
}
}
};
subThread.start();
// _____________________________ create a simple publisher
ZMQ.Socket publishSocket = context.socket(ZMQ.PUB);
publishSocket.bind("tcp://*:31216");
try {
Thread.sleep(3000); // + wait 3 sec to make sure its ready
} catch (InterruptedException e) {
e.printStackTrace();
fail();
}
// publish a sample message
try {
publishSocket.send("TestTopic".getBytes(), ZMQ.SNDMORE);
publishSocket.send("This is test string".getBytes(), 0);
subThread.join(100);
} catch (InterruptedException e) {
e.printStackTrace();
fail();
}
assertTrue(counter.get() > 0);
System.out.println(counter.get());
}
}
Now as you can see, in the subscriber if I use a simple .recv(ZMQ.DONTWAIT) method, it works perfectly. However, if I am using the direct byte buffer I got nothing returned - and I got the following exception, seems like on program exit:
Exception in thread "Thread-0" org.zeromq.ZMQException: Resource temporarily unavailable(0xb)
at org.zeromq.ZMQ$Socket.recvZeroCopy(Native Method)
at ZMQReadynessTest$1.run(ZMQReadynessTest.java:48)
I also tried to use a simple ByteBuffer (not a direct buffer), which doesn't throw the exception above; but also return me nothing.
Does anybody know how to resolve the above?
I don't want to create byte[] objects all around, as I am doing some high performance system. If this cannot be resolved, I might simply use Unsafe instead. But I really want to work in the "supposed way".
Thanks in advance.
Alex
I am creating a multiplayer game in Java with a server and multiple clients. Everything runs perfectly, until I press the Kick-button in the server to kick a client.
Error at receive thread of server, after kicking the first person who joined out of three:
java.lang.IndexOutOfBoundsException: Index: 2, Size: 2
at java.util.ArrayList.rangeCheck(ArrayList.java:604)
at java.util.ArrayList.get(ArrayList.java:382)
> at networktest.Server$3.run(Server.java:186)
at java.lang.Thread.run(Thread.java:722)
The pointed line is the ois = new ObjectInputStream where I receive datatype in the server receive thread. The server kicks the first person perfectly, but removes the second one in the list too, with an error of java.lang.ClassCastException.
server receive:
private static Thread receive = new Thread()
{
#Override
public void run()
{
ObjectInputStream ois;
while (true)
{
for (int i = 0; i < list_sockets.size(); i++)
{
try
{
ois = new ObjectInputStream(list_sockets.get(i).getInputStream());
int receive_state = (Integer) ois.readObject(); // receive state
ois = new ObjectInputStream(list_sockets.get(i).getInputStream());
byte datatype = (byte) ois.readObject(); // receive datatype
if(datatype == 2){
ois = new ObjectInputStream(list_sockets.get(i).getInputStream());
ChatLine chatLine = (ChatLine) ois.readObject(); // receive ChatLine
} else if (datatype == 0){
ois = new ObjectInputStream(list_sockets.get(i).getInputStream());
DataPackage dp = (DataPackage) ois.readObject(); // receive dp
list_data.set(i, dp);
}
if (receive_state == 1) // Client Disconnected by User
{
disconnectClient(i);
i--;
}
}
catch (Exception ex) // Client Disconnected (Client Didn't Notify Server About Disconnecting)
{
System.err.println("Error # receive:");
ex.printStackTrace();
disconnectClient(i);
i--;
}
}
try {
this.sleep(3);
} catch (InterruptedException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
user send:
Thread send = new Thread()
{
public void run()
{
ObjectOutputStream oos;
byte datatype = 0;
while (connected){
if (socket != null){
try {
DataPackage dp = new DataPackage();
dp.x = Client.player.x;
dp.y = Client.player.y;
dp.username = username;
dp.charType = charType;
dp.walking = (byte)Client.player.walking;
if (Client.outputChatLine.line != null)
datatype = 2;
else {
datatype = 0;
}
oos = new ObjectOutputStream(socket.getOutputStream());
oos.writeObject(Integer.valueOf(Client.this.state)); // send state
oos = new ObjectOutputStream(socket.getOutputStream());
oos.writeObject(Byte.valueOf(datatype)); // send datatype
if (datatype == 2)
{
oos.reset();
oos.writeObject(Client.outputChatLine);
Client.outputChatLine = new ChatLine();
} else {
oos = new ObjectOutputStream(socket.getOutputStream());
oos.writeObject(dp);
}
if (Client.this.state == 1) {
connected = false;
socket = null;
JOptionPane.showMessageDialog(null, "Client Disconnected", "Info", 1);
System.exit(0);
}
}
catch (Exception ex){}
}
try {
this.sleep(2);
} catch (InterruptedException ex) {
Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
disconnect client method:
public static void disconnectClient(int index)
{
try
{
list_clients_model.removeElementAt(index);
list_client_states.remove(index);
list_data.remove(index);
list_sockets.remove(index);
}
catch (Exception ex) {}
}
Does anyone know how to solve this?
It looks like you're expecting some other thread to fill some data into list_sockets while you're sleep(3)ing. But you have no synchronization to ensure that this happens only while you're sleeping.
It could equally well happen that the other thread is updating list_sockets simultaneously with your own thread calling list_sockets.get(i). And the ArrayList implementation it is almost certainly not written to have two different of its methods executing simultaneously in two different threads. For example, the other thread could be in the middle of resizing the backing array when you're trying to read an element, and then any crazy thing can go wrong, including the error you're seeing.
You need to learn about inter-thread synchronization. At the very least you need synchronized blocks to protect access to shared data structures. And while you're at it; look at wait/notify or some higher-level concurrency tools to get rid of that horrible 3-millisecond polling loop -- instead have the thread that drops work into the list explicitly wake up the worker thread.
I have an ObjectOutputStream and an ObjectInputStream. I try to send ints and objects through them. Now I manage to send through and read up to a point and I don't know why it stops there.
Here is the point:
Reader:
while (true) {
start = in.readInt();
System.out.println("PART 1");
int temp1 = in.readInt();
int temp2 = in.readInt();
int temp3 = in.readInt();
System.out.println("PART12");
Chunk temp = new Chunk(temp1,temp2, temp3);
while (true) {
It doesn't get to part12 (doesn't pass the first int...)
Writer:
if (chunkList != null) {
for (Chunk c: chunkList) {
out.writeInt(-1);
out.writeInt(c.getLocation().getX());
out.writeInt(c.getLocation().getY());
out.writeInt(c.getLocation().getZ());
if (c.getTileList() != null) {
it passes all of it successfully.
I am every 2ms out.flushing in a separate thread.
Thread:
while (true)
{
while (c.sendPacket()) {
try
{
if (c.getOut() != null)
{
c.getOut().flush();
}
}
catch (IOException ioexception)
{
ioexception.printStackTrace();
}
try
{
sleep(2L);
}
catch (InterruptedException interruptedexception) { }
}
}
Why does it stop reading at the part with the 3 ints?
I have a feeling that this is a thread-safety issue. As a general rule, streams are not designed to be thread-safe. So, unless the you are synchronizing the two threads at a higher level, one thread writing to a stream and a second thread calling flush is unsafe.