Object Level Locking In Java Threads
Apr 16, 2014
I know that below code would put a lock on current instance of DemoClass, What I am not sure of is the role of lock on Object Class in second example. How does below works - Is it putting a lock on Object Class? If yes how will putting a lock on Object? I mean, locking DemoClass ensure no two threads access it concurrently, how does this apply to Object class?
private final Object lock = new Object();
synchronized (lock)
public class DemoClass
{
public void demoMethod(){
synchronized (this)
[code]....
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Jul 21, 2014
I want to implement new locking mechanism similar to like how threads locking or synchronized does the operation. Any inputs to implement out own locking mechanism ?
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May 21, 2014
My multi threaded application processes and loads records into an ECM repository. For reconcliation purposes , I am trying to build an XML format report with the results of the processing per record, while processing is underway per thread. The method below is called from every thread wvery time its ready to append an element to the DOM with the status.
public void writeReportLine(Element rptLine) {
// Write output to report file
synchronized (XMLReportHandler.class) {
reportOutput.getDocumentElement().appendChild(rptLine);
}
}
After all processing completes, the below method is called only once by every thread to write to the File on the file system:
public void writeToReportFile() {
synchronized (XMLReportHandler.class) {
try{
//write the content into xml file
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(reportOutput);
[Code] ....
The problem is that when under load, the threads just seem to hang while the transformer.transform(source, result) call keeps getting executed until there is an interrupt of some sort. I was able to examine a section of what was appended and it was status for records that had finished processing very early in the process based on my application logs. Once an interrupt is recieved , it looks like the threads recover.
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Mar 24, 2014
I need a small example of an object which is visible to two different threads.
Does saying "an object is visible to two threads" mean that it's fields or methods are being used in both the threads? I am not clear about that.
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Mar 2, 2015
I finally made the app to draw 10x10 map out of 50x50 pixel blocks.Now I can't imagine how to make a camera and lock it on character. I know how to make a character, but I just want to understand how locking the camera on character would look.
package tiled;
import org.newdawn.slick.*;
import org.newdawn.slick.state.*;
public class play extends BasicGameState {
int xSize = 10;
int ySize = 10;
[code]....
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Feb 5, 2014
I have this web app in Glassfish which, among other things, monitors consultations in some DB. It's a JEE-EAR app, three layers. Pretty boring until now. Now, there's another WAR-app on Tomcat that processes files through threads. These threads represent an Excel file processed one row at a time.
I need to know when one of those threads are created, when they're alive and when they're terminated, from the Glassfish app.
I need to monitor these batch processes.
I think I could insert the thread ID from the tomcat app in some DB and when it dies, delete it. The glassfish app would query that BD and see if there is one of those batch processes running.
I understand that a thread ID can be recycled but I can find a way to make every process unique.
My first question, would this be viable?
My second question is, could I uniquely set the thread name and then ask for it from the glassfish app to the tomcat-app process thread set? I mean, without a DB in the middle?
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Aug 27, 2014
I have a problem where i cant seem to get this simple delete command working. Everytime i run it it just locks the database and crashes
The id parameter exists in the database the database is small. Only a few tables. update commands work completely fine.
The id is an in and resulting command is - DELETE from Employees where ID = 2;
public static void EmployeeDeleteByID(int idIn){
Connection c = null;
Statement stmt = null;
try {
c = Connect();
c.setAutoCommit(false);
System.out.println("Opened database successfully");
[code]....
Error after running : java.sql.SQLException: database is locked
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Feb 24, 2014
I am trying to write a program in Java that uses threads.Below is the program requirements:The goal of this assignment is to create a routine which creates multiple threads, has them do work in parallel, and terminates when the last thread has finished.
The Scenario: There are several groups of people in a bar watching the Olympics cheering for their country. Each group will cheer for their country some given number of times, with a random pause (between 2 and 5 seconds) between each cheer. There is enough room at the bar for up to ten different groups to sit (each would be cheering for a different country).
The Program: The task is to write a program that will simulate these cheers using threads. The program should be called cheer.X (X being the language of choice). You may use any language that supports threading. When the program is run it should ask for the number of countries and then the name and how many times it will be cheered for. The main function will then create a thread for each team and each thread is responsible for cheering the specified number of times for the correct team at the random interval. You will submit the proper source code file for me to open and compile myself, not an executable.
An example run would look something like this: How many countries are supported at the bar? 3 Enter the first: China How many cheers? 2 Enter the second: USA How many cheers? 4 Enter the third: Russia
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Nov 17, 2014
I am working on a game engine with java. I have come to the final stages of the development of this engine now and need a small hand. For this i am using java's built in libary for graphics. and am strugling to create a nice looking GUi with it, What i need:
The class extends the canvas class and adds it to the jframe, i have set the window up as standard and added a menubar, and net the canvas, what I want to do.
For those of you that have used application such as tiled (shown here [URL] .....) what i am wanting to do is create a gui around the canvas similar to this where the parts on the right are resizable up and down and in and out. i was wondering how i would go about incorporating this.
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Apr 29, 2014
I'm using "standard-kepler-SR2-win32-x86_64" and have installed "jdk-8u5-windows-x64".
But eventhough I can't override a methode like that "@override", it still says me:"annotations are only available, if source lever is 1.5 or greater".
Fine, therefore I installad "jdk-8u5-windows-x64", its the higest one on that oracle side, what else is needed?
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Jan 7, 2015
I have come across some code where it attempts to save an entity to a database, but before it does it validates that the name of the entity is unique. If it is not unique it throws a runtime exception. This results in the ugly default exception web page being displayed. Is there any way to propagate this back to the JSF page where the user enters and clicks the form button to save the entity? The page already handles some error cases such as "field required" using the h:inputText's 'required' attribute. Need something more for name validation.
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Feb 11, 2014
if I declare
class Example
{
int x=10;
......
}
It is not showing any error but when I declare
class Example
{
int x;
x=10;
............
}
it showing compile time error ....
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Jun 29, 2014
Can we set the class path for one level down the current directory? My structure is like
binlibresourceshexicon.cmdinside the folder dist.
In this case I could run the .cmd file which has java -cp .;lib;resources client.Test .
c: rycpdist>java hexicon.cmdBut if i put the .cmd file inside bin as like this and run as
c: rycpdistin>java hexicon.cmdI am getting this error Error: Could not find or load main class
Is there any possibility to set the class path in this case
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Apr 6, 2015
We are working with LinkedBinarySearchTrees. One of specs on my assignment is to "Using a level-order traversal, create a 2-D display of your trees, using the forward and back slashes as the branch lines. The tree nodes should be spaced proportionally to show the structure of the tree neatly."
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Jun 3, 2014
From the tutorial:instance variables can be declared in class level before or after use.But the code below does not compile. Why?
Java Code:
public class MainApp {
i=5;
public static void main(String[] args) {
System.out.println("Hello World");
}
int i;
} mh_sh_highlight_all('java');
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Sep 28, 2014
I need to do a simulation on the assembly code level by writing a mini-compiler for each ISA, i.e., 4, 3, 2-Address Architecture, Accumulator Architecture, Stack Architecture, and Load-Store Architecture.The input to the simulator is a segment of C program:The basic sample segments of C code are:
1. A = (B + C) * D - E;
2. F = (G + H) - (I + J);
3. G = H + A[I];
4. If (I == J) F = G + H;
Else F = G - H;
5. Loop: G = G + A[I];
I = I + J;
If (I != H) Goto Loop;
6. If (G < H) Goto Less;
7. While (save[I] == K)
I = I + J;
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Jun 13, 2014
I need creating a code that will create random addition or subtraction from 0-500 depending on their grade level. I know how to create a random for the math and subtraction. I just dont know how to get it to change depending on their grade level. Example I need it to ask their name, grade level, addition or subtraction then five addition or subtraction questions depending on what they chose.
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Jun 3, 2014
As web server has multiple threads to serve client requests in Thread Pool & to ensure Thread Safety we should not use any variables or Objects at Instance/Class level.But in case of Session Variable which one is the Best Practice as the Session object is used by all the requests to have the same Session ID.
My Code :
public class MyServlet extends HttpServlet {
private static Logger log = Logger.getLogger(ClientRegistrationServlet.class);
private HttpSession session; /* This is used at Instance Level*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
[code]....
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Apr 20, 2014
I'm new to Java and trying to write code a Java program on Mac OS X using IntelliJ. My program uses the SWT library and contains two class's; the first called "view" and the second called "main". The "view" class defines the SWT objects, extends the "Thread" class and contains a "run" method;
public void run() {
initComponents();
while (!display.isDisposed()) {
if (!display.readAndDispatch()) {
display.sleep();
[code]....
I searched for a solution and saw that I have to use the "-XstartOnFirstThread" parameter to JVM. I'm trying it with no success.
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Apr 28, 2014
I making a program that a client connect to a server, then it's starts changing information throw the socket. The info is String. When connection with one open client everything is working great. The problem starts when I connect 2 or more clients simultaneously.
The server doesn't know how to handle each request so it's send info to both the client info that is wrong. If I run several clients and then execute the last client that opens he will work fine the others will crush. On the server I'm getting connection reset. The problem i believe is with the closing socket and thread holding.
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Mar 11, 2015
Here is what I am trying to do:
Write a program to print the even numbers and the odd numbers between 0 and 30 using a single thread and then again using multiple threads.
I already finished the single-threaded program but am having trouble with the multi-threaded one. I have three classes; one class for odd numbers, one for even numbers, and one to execute the code. Here is my code so far:
Even Numbers:
Java Code:
public class EvenNumbers extends Thread {
public void run() {
for (int i=1; i<=30; i++) {
if (i%2 == 0) {
System.out.println("Even number " + i);
[Code] ....
Unfortunately, my output ends up looking a little weird:
Java Code:
C:UsersREDACTEDDropboxSchoolworkREDACTEDJava ProgrammingUnit 5 - Exception
Handling, AssertionsProgram - Thread>java MultiThread
Even Numbers:
Odd Numbers:
Even number 2
[Code] .....
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May 30, 2014
I'm reading the following section of the Oracle docs:
Guarded Blocks (The Java Tutorials > Essential Classes > Concurrency)
We have multiple threads. One of them sets the joy flag to true. The other waits until joy flag is set to true in order to print to the output stream. Rather than squander processer resources with a while loop, we choose to use the wait method of Object which suspends execution of thread. When the other thread throws an exception, we check the loop condition again.
Java Code:
public synchronized void guardedJoy() {
// This guard only loops once for each special event, which may not
// be the event we're waiting for.
while(!joy) {
try {
wait();
} catch (InterruptedException e) {}
}
System.out.println("Joy and efficiency have been achieved!");
} mh_sh_highlight_all('java');
The documentation goes on to state the following:
When a thread invokes d.wait, it must own the intrinsic lock for d - otherwise an error is thrown. Invoking wait inside a synchronized method is a simple way to acquire the intrinsic lock. When wait is invoked, the thread releases the lock and suspends execution.
The statement seems somewhat contradictory. When we invoke wait inside a synchronized method, is the intrinsic lock acquired or released? I thought it was the synchronized keyword itself that acquired the intrinsic lock.
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Aug 16, 2012
I created an instant messenger using java. When I have the Server that communicates between the clients and one client running on my Computer the CPU Usage is at 100%. It really slows down everything else I'm doing and I figure this might be an issue if I gave this to people to use. I don't want the client taking up a lot of CPU Usage if they're just running it in the background while doing other things on their computer. The program utilizes multithreading. Each thread is constantly being polled for input.
The Server, as seen below, has two threads. I explain what the threads do before the code. There is also another while loop running constantly in the server that is waiting for sockets to connect. The loop does not run constantly at the line socket.accept(); it stops and just waits.
The User, split into a menu and chat window, has two threads as well. I explain what the threads do before the code. After I originally posted I put a 100 ms sleep in all my threads. CPU Usage is still at 100%*
This thread listens for input from the user. The input tells the server what action to take. There is a thread running for every user currently connected to the server.
public void run()
{
try
{
input = new DataInputStream(user.getSocket().getInputStream());
output = new DataOutputStream(user.getSocket().getOutputStream());
[code]....
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Jul 22, 2014
I have a console application. One thread allows a user to directly input into a console. Another thread listens on a tcp port, takes input, processes it, and then writes it to the console. The work in different threads, but in tcp thread, one I call a method outside that thread that writes to console, it often gets stuck. here is a mockup of situation:
Java Code:
import java.io.BufferedReader;
import java.io.Console;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
[Code] ......
It often freezes on "Attempt 1". Before I used System.out there, I also tried console.writer() there but both freeze at that point often. Any situation where console or System.out.writeln freeze when working across threads and why it is occurring? It almost feels like one thread has locked the console so the others can't write to it.
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Nov 30, 2014
I have been working on this program for a while and now i seem to be stump it throws an outof Bound array exception error, this program is a matrix multiplication program and spits out the resulting matrix using multithreading. i have a running one and result is
2 -1 0
1 0 3
-1 1 3
but this program's result is:
2 0 0
1 0 0
-1 0 0
it reads a txt document as an commandline arguement the text file reads just like this below:
3 2 2 3
1 0
0 1
-1 1
2 -1 0
1 0 3
the following is my code:
import java.util.*;
import java.io.*;
public class P3 {
public static int matrix1[][];
public static int matrix2[][];
[code].....
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Apr 18, 2014
Actually, i want to create multiple ball using multithreading.I have created a class 'CreateBall' and this class is making ball and second class 'Balls' is a Panel where the ball is display.But only one ball is being displayed.
Here is my code.......
CreateBall.java
import java.awt.*;
public class CreateBall implements Runnable
{
int px,py;
int w=20,h=20;
Graphics g;
public CreateBall(int px,int py)
[Code] .....
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