Following scenario that explains my problem.
I've a PLC that acts as a server socket program. I've written a Client Java program to communicate through socket communication with the PLC.
Steps that take place in this process are:
1) For each second my Client program happen to communicate with the PLC, read the data in stream, store the data temporarily in a ByteArrayOutputStream and closing both input stream and socket. Following snippet gives the idea
try {
socket = new Socket(host, port);
is = socket.getInputStream();
outputBuffer = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int read;
if((read = is.read(buffer)) != -1) {
outputBuffer.write(buffer, 0, read);
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
System.out.println("Before closing the socket");
try {
is.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("After closing the socket");
} catch (Exception e) {
e.printStackTrace();
}
}
2) Processing stored data according to my requirement is what I'm trying to do. So for every 1 second, client program connects to Server, read the data(if data is present), store the data, close socket and process it. And it has to happen for a very long run, probably till the Server program is on. And that may happen till for every few weeks.
3) Problem what I'm facing is, I'm able to run the above show for 1-2 hours, but from then, Client Program unable to fetch the data from the Server Program(PLC in this case), though both are connected through socket. I.e 128 bytes of data present, but Client program isn't able to read that data. And this started happening after program run successfully for almost 2hours
4) Please find the brief code which may help for you to look into.
public class LoggingApplication {
public static void main(String[] args) throws NumberFormatException {
if (args.length > 0 && args.length == 2) {
String ipAddress = mappingService.getIpAddress();
int portNo = (int) mappingService.getPortNo();
ScheduledExecutorService execService = Executors.newScheduledThreadPool(1);
execService.schedule(new MyTask(execService, ipAddress, portNo, mappingService), 1000, TimeUnit.MILLISECONDS);
} else {
throw new IllegalArgumentException("Please pass IPAddress and port no as arguments");
}
}
}
Runnable Code:
public class MyTask implements Runnable {
public ScheduledExecutorService execService;
private String ipAddress;
private int portNo;
private ConfigurationMappingService mappingService;
private MySocketSocketUtil mySocketSocketUtil;
public MyTask(ScheduledExecutorService execService, String ipAddress, int portNo, ConfigurationMappingService mappingService) {
this.execService = execService;
this.ipAddress = ipAddress;
this.portNo = portNo;
this.mappingService = mappingService;
}
public void run() {
MySocketSocketUtil mySocketSocketUtil = new MySocketSocketUtil(ipAddress, portNo);
execService.schedule(new MyTask(execService, ipAddress, portNo, mappingService), 1000, TimeUnit.MILLISECONDS);
mySocketSocketUtil.getData(); //It's able to fetch the data for almost 2 hours but from then, it's just getting empty data and it's keep on giving empty data from then. and so on.
/*
*
*Some code
*/
}
}
Here's where, I'm having the problem
mySocketSocketUtil.getData(); is able to fetch the data for almost 2 hours but from then, it's just getting empty data and it's keep on giving empty data from then. and so on. It's a big question I know, And I want to understand what might have gone wrong.
Edit: I'm ignoring the condition to check end of the stream and closing a socket based on it is because, I knew I'm going to read first 1024 bytes of data only always. And So, I'm closing the socket in finally block
socket = new Socket(host, port);
if(socket != null && socket.isConnected())
It is impossible for socket to be null or socket.isConnected() to be false at this point. Don't write pointless code.
if((read = is.read(buffer)) != -1) {
outputBuffer.write(buffer, 0, read);
};
Here you are ignoring a possible end of stream. If read() returns -1 you must close the socket. It will never not return -1 again. This completely explains your 'empty data':
from then, it's just getting empty data and it's keep on giving empty data from then, and so on
And you should not create a new Socket unless you have received -1 or an exception on the previous socket.
} else {
System.err.println("Socket couldn't be connected");
}
Unreachable: see above. Don't write pointless code.
You should never disconnect from the established connection. Connect once in the LoggingApplication. Once the socket is connected keep it open. Reuse the socket on the next read.
I think there are couple of points you need to fix before getting to the solution to your problem. Please try to follow the following suggestions first:
As #EJP said this code block is not needed.
if(socket != null && socket.isConnected()) {
also you are using a byte array of length 1024 and not using while or for loop to read the data stream. Are you expecting only a block of data which will never exceed 1024 bytes?
byte[] buffer = new byte[1024];
int read;
if((read = is.read(buffer)) != -1) {
This is also not needed as it is unreachable.
} else {
System.err.println("Socket couldn't be connected");
}
Can you explain the data stream behavior you are expecting?
Last but not the least is.read(buffer) is a blocking call so if there is no data to read yet, it will hold the thread execution at that point.
Please try to answer the questions I have asked.
#KishoreKumarKorada from your description in the comment section, it seems like you are monitoring the data change on server side. Socket stream works in a read-once fashion. So,
First thing is, you need to request from server every time and the server needs to RESEND the data on every request.
Second, the way you presented is more like you are operating on byte level, which is not very good way to do that unless you have any legitimate reason to do so. The good way is to wrap the data in JSON or XML format and send it over the stream. But to reduce bandwidth consumption, you may need to operate on byte stream sometimes. You need to decide on that.
Third, for monitoring the data change, the better way is to use some timestamp to compare when the data has changed on the server side and what is the timestamp stored on the client side, if they match, data has not changed. Otherwise fetch the data from the server side and update the client side.
Fourth, when there is data available that you are not able to read, can you debug the ins.read(...) statement to see if its getting executed and the execution goes inside the if block or if statement is evaluated to false? if true then examine the read value and let me know what you have found?
Thanks.
Related
I've created a client-server connection, something like a chat system. Previously I was using a while loop on the client side, and it was waiting to read a message from the console every time (of course server has a while loop as well to serve forever). But now, I'm trying to first create a connection at the beginning of the session, and then occasionally send a message during the session, so to maintain a permanent and persistent connection.
Currently, without the while loop, the client closes the connection and I don't know how to find a workaround.
Here is the client code:
import java.net.*;
import java.io.*;
public class ControlClientTest {
private Socket socket = null;
// private BufferedReader console = null;
private DataOutputStream streamOut = null;
public static void main(String args[]) throws InterruptedException {
ControlClientTest client = null;
String IP="127.0.0.1";
client = new ControlClientTest(IP, 5555);
}
public ControlClientTest(String serverName, int serverPort) throws InterruptedException {
System.out.println("Establishing connection. Please wait ...");
try {
socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
start();
} catch (UnknownHostException uhe) {
System.out.println("Host unknown: " + uhe.getMessage());
} catch (IOException ioe) {
System.out.println("Unexpected exception: " + ioe.getMessage());
}
String line = "";
// while (!line.equals(".bye")) {
try {
Thread.sleep(1000);
//TODO get data from input
// line = console.readLine();
line="1";
if(line.equals("1"))
line="1,123";
streamOut.writeUTF(line);
streamOut.flush();
} catch (IOException ioe) {
System.out.println("Sending error: " + ioe.getMessage());
}
// }
}
public void start() throws IOException {
// console = new BufferedReader(new InputStreamReader(System.in));
streamOut = new DataOutputStream(socket.getOutputStream());
}
}
And here is the Server code:
import java.awt.*;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class ControlServer {
private Socket socket = null;
private ServerSocket server = null;
private DataInputStream streamIn = null;
public static void main(String args[]) {
ControlServer server = null;
server = new ControlServer(5555);
}
public ControlServer(int port) {
try {
System.out
.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
System.out.println("Waiting for a client ...");
socket = server.accept();
System.out.println("Client accepted: " + socket);
open();
boolean done = false;
while (!done) {
try {
String line = streamIn.readUTF();
// TODO get the data and do something
System.out.println(line);
done = line.equals(".bye");
} catch (IOException ioe) {
done = true;
}
}
close();
} catch (IOException ioe) {
System.out.println(ioe);
}
}
public void open() throws IOException {
streamIn = new DataInputStream(new BufferedInputStream(
socket.getInputStream()));
}
public void close() throws IOException {
if (socket != null)
socket.close();
if (streamIn != null)
streamIn.close();
}
}
I would like to summarize some good practices regarding the stability of TCP/IP connections which I apply on a daily basis.
Good practice 1 : Built-in Keep-Alive
socket.setKeepAlive(true);
It automatically sends a signal after a period of inactivity and checks for a reply. The keep-alive interval is operating system dependent though, and has some shortcomings. But all by all, it could improve the stability of your connection.
Good practice 2 : SoTimeout
Whenver you perform a read (or readUTF in your case), your thread will actually block forever. In my experience this is bad practice for the following reasons: It's difficult to close your application. Just calling socket.close() is dirty.
A clean solution, is a simple read time-out (e.g. 200ms). You can do this with the setSoTimeoutmethod. When the read() method timeouts it will throw a SocketTimeoutException. (which is a subclass of IOException).
socket.setSoTimeout(timeoutInterval);
Here is an example to implement the loop. Please note the shutdown condition. Just set it to true, and your thread will die peacefully.
while (!shutdown)
{
try
{
// some method that calls your read and parses the message.
code = readData();
if (code == null) continue;
}
catch (SocketTimeoutException ste)
{
// A SocketTimeoutExc. is a simple read timeout, just ignore it.
// other IOExceptions will not be stopped here.
}
}
Good practice 3 : Tcp No-Delay
Use the following setting when you are often interfacing small commands that need to be handled quickly.
try
{
socket.setTcpNoDelay(true);
}
catch (SocketException e)
{
}
Good practice 4 : A heartbeat
Actually there are a lot of side scenario's that are not covered yet.
One of them for example are server applications that are designed to only communicate with 1 client at a time. Sometimes they accept connections and even accept messages, but never reply to them.
Another one: sometimes when you lose your connection it actually can take a long time before your OS notices this. Possibly due to the shortcomings described in good practice 3, but also in more complex network situations (e.g. using RS232-To-Ethernet converters, VMware servers, etc) this happens often.
The solution here is to create a thread that sends a message every x seconds and then waits for a reply. (e.g. every 15 seconds). For this you need to create a second thread that just sends a message every 15 seconds. Secondly, you need to expand the code of good practice 2 a little bit.
try
{
code = readData();
if (code == null) continue;
lastRead = System.currentTimeMillis();
// whenever you receive the heart beat reply, just ignore it.
if (MSG_HEARTBEAT.equals(code)) continue;
// todo: handle other messages
}
catch (SocketTimeoutException ste)
{
// in a typical situation the soTimeout is about 200ms
// the heartbeat interval is usually a couple of seconds.
// and the heartbeat timeout interval a couple of seconds more.
if ((heartbeatTimeoutInterval > 0) &&
((System.currentTimeMillis() - lastRead) > heartbeatTimeoutInterval))
{
// no reply to heartbeat received.
// end the loop and perform a reconnect.
break;
}
}
You need to decide if your client or server should send the message. That decision is not so important. But e.g. if your client sends the message, then your client will need an additional thread to send the message. Your server should send a reply when it receives the message. When your client receives the answer, it should just continue (i.e. see code above). And both parties should check: "how long has it been?" in a very similar way.
You could wrap a thread around the connection and have it periodically send a status to keep the line open, say every 30 seconds or whatever. Then, when it actually has data to send it would reset the keep alive to be 30 seconds after the last transmission. The status could be helpful to see if the client is still alive anyway, so at least it can be a useful ping.
Also, you should change your server code, you appear to only handle one connection at the moment. You should loop and when a socket connection comes in spawn a thread to handle the client request and go back to listening. I may be reading to much into what may just be your test code, though.
Make the client socket connection wrapped around a thread. Use a blocking queue to wait for messages. There should only be a single sender queue throughout your application, so use a singleton pattern.
e.g.
QueueSingleton queue = QueueSingleton.getSenderQueue();
Message message = queue.take() // blocks thread
send(message); //send message to server
When you need to send a message to the server, you can use the blocking queue to send the message.
QueueSingleton queue = QueueSingleton.getSenderQueue();
queue.put(message)
The client thread will wake up and process the message.
For maintaining the connection, use a timer task. This is special type of thread that calls a run method repetitively at specified periods. You can use this to post a message, a ping message, every so often.
For processing the received message, you could have another thread, waiting for messages on another blocking queue (receiver queue). The client thread will put the received message on this queue.
I have a library which I need to improve since it is dropping to many packets. I want to receive a RTP-Stream, but the streamer is sending bursts of 30-40 packets within a millisecond (MJPEG-Stream). I can see the packets being complete when monitoring traffic in Wireshark. But when trying to receive them in Java, I lose a lot of those packets.
I have already been able to improve the libraries behavior by implementing a ring buffer that would constantly get filled whenever a packet is available and a separate reader thread that reads from this buffer. But I'm still not able to get all the packets from my socket that I can see in wireshark. Through RTP sequence numbers I can monitor in the reader thread if the packet processed is the one expected.
The following code is handling packet receiving:
private volatile byte[][] packetBuffer = new byte[1500][BUFFER_SIZE];
private volatile DatagramPacket[] packets = new DatagramPacket[BUFFER_SIZE];
private volatile int writePointer = 0;
public void run() {
Thread reader = new RTPReaderThread();
reader.start();
while (!rtpSession.endSession) {
// Prepare a packet
packetBuffer[writePointer] = new byte[1500];
DatagramPacket packet = new DatagramPacket(packetBuffer[writePointer], packetBuffer[writePointer].length);
// Wait for it to arrive
if (!rtpSession.mcSession) {
// Unicast
try {
rtpSession.rtpSock.receive(packet);
} catch (IOException e) {
if (!rtpSession.endSession) {
e.printStackTrace();
} else {
continue;
}
}
} else {
// Multicast
try {
rtpSession.rtpMCSock.receive(packet);
} catch (IOException e) {
if (!rtpSession.endSession) {
e.printStackTrace();
} else {
continue;
}
}
}
packets[writePointer] = packet;
this.incrementWritePointer();
synchronized (reader) {
reader.notify();
}
}
}
What I already know:
I know that UDP is allowed to lose packets, but I still want to
achieve the best possible result. If wireshark can see the packet, I
want to be able to retrieve it as well, if possible.
I know that the ring buffer is never full while losing packets, so
this doesn't make me lose packets either. I tried with BUFFER_SIZES
of 100 and even 1000, but I already lose the first packets before a
total of 1000 packets has been send.
So the question is: what is best practice to receive as many packets as possible from a DatagramSocket? Can I improve handling of packet bursts?
Try setting the SO_RCVBUF size on the datagram socket with rtpSock.setReceiveBufferSize(size). This is only a suggestion to the OS, and the OS may not honor it, especially if it is too large. But I would try setting it to (SIZE_OF_PACKET * 30 * 100), where 30 is for the number of packets in a burst, and 100 is a guess of the number of milliseconds where you will not be able to keep up with the arrival speed.
Note that if your code cannot keep up with processing at the arrival speed in general, the OS has no choice but to drop packets.
My application uses sockets and threads to send real-time data that is receiving to clients that connect to it. To do so, the steps are:
Connects to the data server and then waits for clients
Launch a thread to discuss incoming data, format them and send them out to customers, if any.
When a client connects, it opens a thread for him through which data will be sent.
Finally, use another thread to test you are receiving and sending data, otherwise it is reconnected to the source.
The data received from the source are stored in an array waiting to be processed by the thread.
In each client thread, the received data is also stored in an array to be sent.
The purpose of this is that no jams in receiving or sending data.
the data is delayed 10 seconds or more to reach customers
What I can do to optimize performance?
This is running on a windows server, can you recommend any profiler?
Thank you very much for your help.
EDIT:
The data are strings of variable length.
A part of code is:
// create source socket in class implements Runnable and then waits client
Socket entrada = new Socket(servidor,Integer.parseInt(puerto));
InputStream sIn = entrada.getInputStream();
while (!error) {
try {
s = salida.accept();
clientes.add(new ClientThread(s));
// run
while (((c = sIn.read()) != -1) && ((clientes.size() > 0))) {
if (c != 13 && c != 10) {
cad += (char) c;
}
if (c == 13) received[i] = cad
// In SendThread, run
// format received[i] and send result
for (i=0; i < clientes.size(); i++) {
clientes.get(i).SendData(result);
}
// In ClientThread:
OutputString s1out = socket.getOutputStream();
// SendData
sending[i] = result;
// run
if cad forsending
for (int j = 0;j<res.length();j++){
try {
s1out.write((int)res.charAt(j));
} catch (Exception e) {
}
}
Thanks.
Depending on how much data you are sending, it could be the way you are handling streams.
c = sIn.read() reads a only a few bytes at a time. Try wrapping it with a BufferedReader and using readLine(). BufferedReader will read a few kb at a time, which is much more efficient. readLine() will also break inputs into lines for you, which will simplify the code somewhat.
On the client connection, PrintWriter may help you to output whole lines in one go.
I have a fairly complex project that boils down to a simple Client / Server communicating through object streams.
Everything works flawlessly for two consecutive connections (I connect once, work, disconnect, then connect again, work, and disconnect). The client connects, does its business, and then closes. The server successfully closes both the object output stream and the socket, with no IO errors.
When I try to connect a third time, the connection appears to go through (the ServerSocket.accept() method goes through and an ObjectOutputStream is successfully created). No data is passed, however. The inputStream.readUnshared() method simply blocks.
I have taken the following memory precautions:
When it comes time to close the sockets, all running threads are stopped, and all objects are nulled out.
After every writeUnshared() method
call, the ObjectOutputBuffer is
flushed and reset.
Has anyone encountered a similar problem, or does anyone have any suggestions? I'm afraid my project is rather large, and so copying code is problematic.
The project boils down to this:
SERVER MAIN
ServerSocket serverSocket = new ServerSocket(port);
while (true) {
new WorkThread(serverSocket.accept()).start();
}
WORK THREAD (SERVER)
public void run() {
ObjectInputBuffer inputBuffer = new ObjectInputBuffer(new BufferedInputStream(socket.getInputStream()));
while (running) {
try {
Object myObject = inputBuffer.readUnshared();
// do work is not specified in this sample
doWork(myObject);
} catch (IOException e) {
running = false;
}
}
try {
inputBuffer.close();
socket.close();
} catch (Exception e) {
System.out.println("Could not close.");
}
}
CLIENT
public Client() {
Object myObject;
Socket mySocket = new Socket(address, port);
try {
ObjectOutputBuffer output = new ObjectOutputBuffer(new BufferedOutputStream(mySocket.getOutputStream()));
output.reset();
output.flush();
} catch (Exception e) {
System.out.println("Could not get an input.");
mySocket.close();
return;
}
// get object data is not specified in this sample. it simply returns a serializable object
myObject = getObjectData();
while (myObject != null) {
try {
output.writeUnshared(myObject);
output.reset();
output.flush();
} catch (Exception e) {
e.printStackTrace();
break;
} // catch
} // while
try {
output.close();
socket.close();
} catch (Exception e) {
System.out.println("Could not close.");
}
}
Thank you to everyone who may be able to help!
(1) What's ObjectInputBuffer and ObjectOutputBuffer? Did you mean ObjectInputStream & ObjectOutputStream?
(2) If so, calling reset() immediately after creating the ObjectOutputStream is just a waste of time and bandwidth.
(3) Why are you printing 'could not get an input' on an exception creating an output stream?
(4) When you get an exception you should always print its message - don't completely substitute it with your own, that's just throwing away useful information.
(5) You are assuming that any IOException when reading means the end of the stream. Only EOFException means that. Any other IOException should be printed or logged. Clearly you are getting some other exception here and ignoring it.
(6) Why do you keep sending the same object?
From ObjectInputStream API for readUnshared():
Reads an "unshared" object from the
ObjectInputStream. This method is
identical to readObject, except that
it prevents subsequent calls to
readObject and readUnshared from
returning additional references to the
deserialized instance obtained via
this call.
Could this be the problem? Use readObject() instead.
This is a follow up to:
this question
Basically, I have a server loop that manages a connection to one solitary client. At one point in the loop, if a ClientSocket exists it attempts a read to check if the client is still connected:
if (bufferedReader.read() == -1) {
logger.info("CONNECTION TERMINATED!");
clientSocket.close();
setUpSocket(); // sets up the server to reconnect to the client
} else {
sendHeartBeat(); // Send a heartbeat to the client
}
The problem is, that once a socket has been created the application will hang on the read, I assume waiting for data that will never come, since the client never sends to the server. Before this was OK, because this correctly handled disconnects (the read would eventually fail when the client disconnected) and the loop would attempt reestablish the connection. However, I now have added the above sendHeartBeat() method, which periodically lets the client know the server is still up. If the read is holding the thread then the heartbeats never happen!
So, I assume I am testing if the connection is still up incorrectly. I could, as a quick hack, run the bufferedReader.read() in a seperate thread, but then I'll have all sorts of concurrency issues that I really don't want to deal with.
So the question is a few fold:
Am I checking for a client disconnect correctly?
If not, how should I do it?
If I am doing it correctly how I do I get the read to not hold the process hostage? Or is threading the only way?
When you create your socket, first set a timeout:
private int timeout = 10000;
private int maxTimeout = 25000;
clientSocket.setSoTimeout(timeout);
With this, if a read times out you'll get java.net.SocketTimeoutException (which you have to catch). Thus, you could do something like this, assuming you've previously set the SO_TIMEOUT as shown above, and assuming that the heartbeat will always get a response from the remote system:
volatile long lastReadTime;
try {
bufferedReader.read();
lastReadTime = System.currentTimeMillis();
} catch (SocketTimeoutException e) {
if (!isConnectionAlive()) {
logger.info("CONNECTION TERMINATED!");
clientSocket.close();
setUpSocket(); //sets up the server to reconnect to the client
} else {
sendHeartBeat(); //Send a heartbeat to the client
}
}
public boolean isConnectionAlive() {
return System.currentTimeMillis() - lastReadTime < maxTimeout;
}
A common way of handling this is setting the timeout to some number (say 10 seconds) and then keeping track of the last time you successfully read from the socket. If 2.5 times your timeout have elapsed, then give up on the client and close the socket (thus sending a FIN packet to the other side, just in case).
If the heartbeat will not get any response from the remote system, but is just a way of ultimately generating an IOException earlier when the connection has fallen down, then you could do this (assuming that the sendHeartBeat itself will not throw an IOException):
try {
if (bufferedReader.read() == -1) {
logger.info("CONNECTION TERMINATED with EOF!");
resetConnection();
}
} catch (SocketTimeoutException e) {
// This just means our read timed out ... the socket is still good
sendHeartBeat(); //Send a heartbeat to the client
} catch (IOException e) {
logger.info("CONNECTION TERMINATED with Exception " + e.getMessage());
resetConnection();
}
....
private void resetConnection() {
clientSocket.close();
setUpSocket(); //sets up the server to reconnect to the client
}
You are checking correctly, you can should add a try catch with IOException in case it occurs.
There is a way to avoid threading, you can use a Selector with a non-bloking socket.
public void initialize(){
//create selector
Selector selector = Selector.open();
ServerSocketChannel acceptSocket = ServerSocketChannel.open();
acceptSocket.configureBlocking(false);
String bindIp = "127.0.0.1";
int bindPort = 80;
acceptSocket.socket().bind(new InetSocketAddress(bindIp, bindPort));
//register socket in selector for ACCEPT operation
acceptSocket.register(selector, SelectionKey.OP_ACCEPT);
this.selector = selector;
this.serverSocketChannel = serverSocketChannel;
}
public void serverStuff() {
selector.select(maxMillisecondsToWait);
Set<SelectionKey> selectedKeys = selector.selectedKeys();
if( selectedKeys.size() > 0 )
{
if( key.isAcceptable() ){
//you can accept a new connection
SocketChannel clientSk = serverSocketChannel.accept();
clientSk.configureBlocking(false);
//register your SocketChannel in the selector for READ operations
clientSk.register(selector, SelectionKey.OP_READ);
} else if( key.isReadable() ){
//you can read from your socket.
//it will return you -1 if the connection has been closed
}
}
if( shouldSendHeartBeat() ){
SendHeartBeat
}
}
You should add error checking in your disconnection detection. Sometimes an IOException may be thrown when the connection to the other end is lost.
I am afraid that threading is unavoidable here. If you don't want to block the execution of your code, you need to create a separate thread.