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Java two threads work with the same data (one get, one set)

I'm taking my first steps with Java Sockets and Threads.
I want to try make synchonized connection with serwer where multiple threades adds their request to the queue and signle thread send all this request. In the meantime other threads wait for there resoults.
How it's work:
Client ask servert to log in by caling method
User user = logIn("sdasd");
public User logIn(String name){
System.out.println("!Log in");
//Function create request
RequestHandler<User> request = new RequestHandler<>("logIn", name, out, results);
//Request is added to queue
requestQueue.addLast(request);
RequestStatus status;
//Thread who call this function wait for request to be handle (changed status)
while (true){
status = request.getStatus();
System.out.println(status);
if (status == RequestStatus.SUCCESSFUL) {
System.out.println("Try to get result: ");
User user = request.result();
System.out.println(user.getName());
return request.result();
}
if(status == RequestStatus.FAILED) {
return null;
}
}
}
In the meantime other thread send request to server:
new Thread(new Runnable() {
#Override
public void run() {
while(isConnected()){
//is request to be handle?
if(requestQueue.size() != 0){
//remove request form queue
RequestHandler request = (RequestHandler) requestQueue.removeFirst();
//change request status
request.setStatus(RequestStatus.IN_PROGRESS);
System.out.println("!Request: ");
System.out.println(request.getStatus());
//process request
request.request();
//change request status to finished
request.setStatus(RequestStatus.SUCCESSFUL);
System.out.print("!Request end: ");
System.out.println(request.getStatus());
}
}
Iterator<Request> iterator = requestQueue.iterator();
for (Iterator<Request> it = iterator; it.hasNext(); ) {
Request request = it.next();
request.setStatus(RequestStatus.FAILED);
}
}
}).start();
Inside class RequestHandler is process this code:
#Override
public void request() {
try {
//send commend
out.writeObject(requestCommend);
//wait for result (other thread handle this functionality)
while(!results.containsKey(commend)){}
//attach result
result = (T) results.remove(commend);
} catch (IOException e) {
e.printStackTrace();
}
}
When the request is send to the server other thread wait for response for the server and add result to the HashMap:
new Thread(new Runnable() {
#Override
public void run() {
while(isConnected()) {
try {
String commend = (String) in.readObject();
if(commend.charAt(0) == '#') { // # mean its result of request
Object object = in.readObject();
//This is debug case to see everything work properly
if(object == null){
System.out.println("!I am null");
}else{
System.out.println("I am user: " +((User) object).getName());
}
System.out.println(commend);
results.put(commend, object);
}
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
}).start();
This is it. Required code for this question:
public class ServerConnection extends Socket{
public static final int PORT = 8888;
private ObjectInputStream in;
private ObjectOutputStream out;
private LinkedList<Request> requestQueue;
private ConcurrentHashMap<String, Object> results;
public ServerConnection() throws IOException{
super("localhost", PORT);
System.out.println("Connected to the server.");
in = new ObjectInputStream(getInputStream());
out = new ObjectOutputStream(getOutputStream());
requestQueue = new LinkedList<>();
results = new ConcurrentHashMap<>();
new Thread(new Runnable() {
#Override
public void run() {
while(isConnected()){
if(requestQueue.size() != 0){
RequestHandler request = (RequestHandler) requestQueue.removeFirst();
request.setStatus(RequestStatus.IN_PROGRESS);
System.out.println("!Request: ");
System.out.println(request.getStatus());
request.request();
request.setStatus(RequestStatus.SUCCESSFUL);
System.out.print("!Request end: ");
System.out.println(request.getStatus());
}
}
Iterator<Request> iterator = requestQueue.iterator();
for (Iterator<Request> it = iterator; it.hasNext(); ) {
Request request = it.next();
request.setStatus(RequestStatus.FAILED);
}
}
}).start();
new Thread(new Runnable() {
#Override
public void run() {
while(isConnected()) {
try {
String commend = (String) in.readObject();
if(commend.charAt(0) == '#') { // # mean its result of request
Object object = in.readObject();
//This is debug case
if(object == null){
System.out.println("!I am null");
}else{
System.out.println("I am user: " +((User) object).getName());
}
System.out.println(commend);
results.put(commend, object);
}
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
}).start();
}
public User logIn(String name){
System.out.println("!Log in");
RequestHandler<User> request = new RequestHandler<>("logIn", name, out, results);
requestQueue.addLast(request);
RequestStatus status;
while (true){
status = request.getStatus();
System.out.println(status);
if (status == RequestStatus.SUCCESSFUL) {
System.out.println("Try to get result: ");
User user = request.result();
System.out.println(user.getName());
return request.result();
}
if(status == RequestStatus.FAILED) {
return null;
}
}
}
public ArrayList<Room> getListOfRooms(){
Request<ArrayList<Room>> request = new RequestHandler<>("listOfRooms", out, results);
requestQueue.addLast(request);
while (true){
RequestStatus status = request.getStatus();
if (status == RequestStatus.SUCCESSFUL)
return request.result();
if(status == RequestStatus.FAILED) {
return null;
}
}
}
}
RequestHandler looks like this:
public class RequestHandler<T> implements Request<T>{
private T result;
private RequestStatus status = RequestStatus.NEW;
private ObjectOutputStream out;
private String commend;
private String requestCommend;
private ConcurrentHashMap<String, Object> results;
public RequestHandler(String commend, String parameters, ObjectOutputStream out, ConcurrentHashMap<String, Object> results) {
this.commend = "#" + commend;
this.requestCommend = "?" + commend + ":" + parameters;
this.out = out;
this.results = results;
}
public RequestHandler(String commend, ObjectOutputStream out, ConcurrentHashMap<String, Object> results) {
this.commend = "#" + commend;
this.requestCommend = "?" + commend;
this.out = out;
this.results = results;
}
#Override
public void request() {
try {
out.writeObject(requestCommend);
while(!results.containsKey(commend)){}
result = (T) results.remove(commend);
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public T result() {
return result;
}
#Override
public RequestStatus getStatus() {
return status;
}
#Override
public void setStatus(RequestStatus status) {
this.status = status;
}
}
The output looks like this WHEN ITS WORK:
Connected to the server.
!Log in
NEW
IN_PROGRESS
...
IN_PROGRESS
!Request: IN_PROGRESS
IN_PROGRESS
...
IN_PROGRESS
I am user: sdsad
#logIn
IN_PROGRESS
IN_PROGRESS
SUCCESSFUL
!Request end: SUCCESSFUL
Try to get result:
sdsad
But when I COMMENT one debug msg I got this:
Connected to the server.
!Log in
!Request: IN_PROGRESS
I am user: dfdsfsdf4324
#logIn
!Request end: SUCCESSFUL
And the loop while(true) never end becouse I got always status IN_PROGRESS.
That's why I want to ask you why it's happen? Is Java have some weird way to optimalize output of functions to make is faster and is it thinking if it was reapet milion times so it has to be this state always?

Why Consumer thread is not able to remove messages from Vector?

I am trying to create a solution for Producer/ Consumer problem where one thread is putting message in Vector and another is removing from it.
import java.util.Vector;
public class Producer implements Runnable {
static final int MAXQUEUE = 5;
private Vector<String> messages;
public Producer(Vector<String> messages) {
super();
this.messages = messages;
}
#Override
public void run() {
try {
while (true)
putMessage();
} catch (InterruptedException e) {
}
}
private synchronized void putMessage() throws InterruptedException {
while (messages.size() == MAXQUEUE) {
wait();
}
messages.addElement(new java.util.Date().toString());
System.out.println("put message");
notifyAll();
}
public static void main(String args[]) {
Vector<String> messages = new Vector<String>();
new Thread(new Producer(messages)).start();
new Thread(new Consumer(messages)).start();
}
}
class Consumer implements Runnable{
public Consumer(Vector<String> messages) {
super();
this.messages = messages;
}
private Vector<String> messages;
public synchronized String getMessage() throws InterruptedException {
notifyAll();
while (messages.size() == 0) {
wait();//By executing wait() from a synchronized block, a thread gives up its hold on the lock and goes to sleep.
}
String message = (String) messages.firstElement();
messages.removeElement(message);
return message;
}
#Override
public void run() {
try {
while (true) {
String message = getMessage();
System.out.println("Got message: " + message);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
Whenever I am running the program, it is printing put message 5 times. I don't understand even after notifyAll(), it is not giving lock to consumer.

Your code is not working because your two threads are not notifying/waiting on the same monitor.
They each notify and wait on their own monitor, not a shared monitor. Change code to use a shared monitor, e.g. messages, including the synchronizations.
private void putMessage() throws InterruptedException {
synchronized (messages) { // <======
while (messages.size() == MAXQUEUE) {
messages.wait(); // <======
}
messages.addElement(new java.util.Date().toString());
System.out.println("put message");
messages.notifyAll(); // <======
}
}
public String getMessage() throws InterruptedException {
synchronized (messages) { // <======
while (messages.size() == 0) {
messages.wait(); // <======
}
String message = (String) messages.firstElement();
messages.removeElement(message);
messages.notifyAll(); // <======
return message;
}
}
Notice that methods are no longer synchronized.

Logging to the console is very slow so if you do this without holding the lock you give the consumer a chance.
#Override
public void run() {
try {
while (true) {
// slows the producer a little to give the consumer a chance to get the lock.
System.out.println("put message");
putMessage();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private void putMessage() throws InterruptedException {
synchronized (messages) {
while (messages.size() == MAXQUEUE) {
messages.wait();
}
messages.addElement(new java.util.Date().toString());
messages.notifyAll();
}
}
BTW on the consumer you can write this
public String getMessage() throws InterruptedException {
synchronized (messages) {
while (messages.isEmpty()) {
messages.wait();//By executing wait() from a synchronized block, a thread gives up its hold on the lock and goes to sleep.
}
messages.notifyAll();
return messages.remove(0);
}
}

How to gracefully wait to job task finish in BlockingQueue java

I am writing a job queue using BlockingQueue and ExecutorService. It basically waiting new data in the queue, if there are any data put into the queue, executorService will fetch data from queue. But the problem is that i am using a loop that loops to wait the queue to have data and thus the cpu usage is super high.
I am new to use this api. Not sure how to improve this.
ExecutorService mExecutorService = Executors.newSingleThreadExecutor();
BlockingQueue<T> mBlockingQueue = new ArrayBlockingQueue();
public void handleRequests() {
Future<T> future = mExecutorService.submit(new WorkerHandler(mBlockingQueue, mQueueState));
try {
value = future.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
if (mListener != null && returnedValue != null) {
mListener.onNewItemDequeued(value);
}
}
}
private static class WorkerHandler<T> implements Callable<T> {
private final BlockingQueue<T> mBlockingQueue;
private PollingQueueState mQueueState;
PollingRequestHandler(BlockingQueue<T> blockingQueue, PollingQueueState state) {
mBlockingQueue = blockingQueue;
mQueueState = state;
}
#Override
public T call() throws Exception {
T value = null;
while (true) { // problem is here, this loop takes full cpu usage if queue is empty
if (mBlockingQueue.isEmpty()) {
mQueueState = PollingQueueState.WAITING;
} else {
mQueueState = PollingQueueState.FETCHING;
}
if (mQueueState == PollingQueueState.FETCHING) {
try {
value = mBlockingQueue.take();
break;
} catch (InterruptedException e) {
Log.e(TAG, e.getMessage(), e);
break;
}
}
}
Any suggestions on how to improve this would be much appreciated!

You don't need to test for the queue to be empty, you just take(), so the thread blocks until data is available.
When an element is put on the queue the thread awakens an value is set.
If you don't need to cancel the task you just need:
#Override
public T call() throws Exception {
T value = mBlockingQueue.take();
return value;
}
If you want to be able to cancel the task :
#Override
public T call() throws Exception {
T value = null;
while (value==null) {
try {
value = mBlockingQueue.poll(50L,TimeUnit.MILLISECONDS);
break;
} catch (InterruptedException e) {
Log.e(TAG, e.getMessage(), e);
break;
}
}
return value;
}

if (mBlockingQueue.isEmpty()) {
mQueueState = PollingQueueState.WAITING;
} else {
mQueueState = PollingQueueState.FETCHING;
}
if (mQueueState == PollingQueueState.FETCHING)
Remove these lines, the break;, and the matching closing brace.

Add a progress bar to a Job in RCP

I have a time consuming job in my RCp application in which I read out a big database and save it in a file. I am running this job in a separate thread so that the UI of my app is not blocked but I dont know how to add a progress bar to this task
My code:
public class MirrorFeatureModel extends Job {
protected class MutexRule implements ISchedulingRule {
public boolean isConflicting(ISchedulingRule rule) {
return rule == this;
}
public boolean contains(ISchedulingRule rule) {
return rule == this;
}
}
private String source;
private String template;
private String target;
public MirrorFeatureModel(String name) {
super(name);
}
public MirrorFeatureModel(String source, String template, String target){
super("Mirroring SWA Model");
this.source = source;
this.template = template;
this.target = target;
}
public void run() {
this.schedule();
}
#Override
protected IStatus run(IProgressMonitor monitor) {
ILog logView = Activator.getDefault().getLog();
String connectionString = this.source;
String emptyEAP = this.template;
String target = this.target;
try{
monitor.beginTask("Copying swa model to local", 1);
new Mirror(connectionString, emptyEAP,target).run();
monitor.worked(1);
}catch(final Exception e) {
logView.log(new Status(Status.ERROR, null , "Failed to create local SAM instance", e));
Display.getDefault().asyncExec(new Runnable() {
#Override
public void run() {
MessageDialog.openError(PlatformUI.getWorkbench().getDisplay().getActiveShell(), "Failed to create local SAM instance", e.getMessage());
}
});
return Status.CANCEL_STATUS;
}
return Status.OK_STATUS;
}
}
Mirror.run() Method
public void run(IProgressMonitor monitor) {
try{
if (monitor != null)
monitor.subTask("Creating directory for eap file");
File tempTarget=File.createTempFile("eap-mirror", "eap");
if (monitor != null)
monitor.worked(1);
try {
if (monitor != null)
monitor.subTask("Establising connection");
this.source=DriverManager.getConnection(com.intel.imc.swa.easql.EaDbStringParser.eaDbStringToJdbc(sourceString));
this.source.setReadOnly(true);
if(monitor != null)
monitor.worked(1);
FileUtils.copyFile(new File(templateFileString), tempTarget);
if (monitor != null)
monitor.subTask("Opening database");
this.target=Database.open(tempTarget,false,false);
if(monitor != null)
monitor.worked(1);
if (monitor != null)
monitor.subTask("Mirroring tables");
Collection<String> tables=selectTables(source);
long time=System.currentTimeMillis();
for (String tableName : tables) {
long tTime=System.currentTimeMillis();
Table table=target.getTable(tableName);
System.out.print("Mirroring table "+tableName+"...");
table.setOverrideAutonumber(true);
copyTable(table, source, target);
System.out.println(" took "+(System.currentTimeMillis()-tTime));
}
System.out.println("Done. Overall time: "+(System.currentTimeMillis()-time));
if(monitor != null)
monitor.worked(1);
} catch (SQLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
How can I add a progress bar in this class that shows me the progress of this job
Thanks

Normally jobs show a progress indicator in the progress view and in the status line at the bottom of the main window.
If you call setUser(true) before schedule() then the job will show a pop-up progress dialog if the job runs for more than a few seconds.
To show job progress you must specify the total amount of work on the beginTask call
monitor.beginTask("...", total work);
and then you must call monitor.worked(xxx) each time you have done part of the work.

Java thread listener

I would like to create a runnable class which contain a list inside. While running, thread will listen to any list changes and process all elements inside. That's my idea.
Below is my code but it still doesn't execute process() when I add new element to list or list changed by . Please give me some help.
public class QueueService implements Runnable {
private List<Request> requestQueue;
public synchronized void add(Request request) {
if (requestQueue == null) {
requestQueue = new LinkedList<Request>();
}
requestQueue.add(request);
LOGGER.info("Added new request");
}
#Override
public void run() {
LOGGER.info("Queue started...");
while (true) {
if (requestQueue != null) {
process();
}
}
}
private synchronized void process() {
try {
Iterator<VMRequest> requests = requestQueue.iterator();
while(requests.hasNext()) {
Request req = requests.next();
// process each element and remove when done
}
} catch (Exception e) {
LOGGER.info(e.getMessage());
}
}
}