Thread.currentThread() ); Meaning
Does anyone know what the output I'm getting from the currentThread method means?
What do the int(s) represent? I've checked the API, it doesn't go into detail about
the return.
Method Detail
currentThread
public static Thread currentThread()
Returns a reference to the currently executing thread object.
Returns:
the currently executing thread.And here's what I'm doing :
System.out.println("currentThread output : " + Thread.currentThread() );
//OUTPUT
Thread[Thread-1,5,main]Edited by: rico16135 on May 3, 2008 1:17 PM
It's all there in the docs.
Read Thread.currentThread's docs. It returns a reference to the Thread object for the currently running thread.
System.out.println calls toString, so look at Thread's toString method.
Also look at Thread's constructors.
Similar Messages
-
Public static Thread currentThread() and multi core processors??
Hello,
I have the following basic question: what does public static Thread currentThread() mean in the context of multi core processors where several threads may execute concurrently?
Any clue welcome,
J.Hi balteo,
When you invoke Thread.currentThread(), you get the reference of the current thread : the thread where you make the call.
Just try :
System.out.println("My program is running thread : " + Thread.currentThread().getName());
mean in the context of multi core processors where several threads may execute concurrently?Several threads may run concurrently with single core processors. The number of concurrent threads you may execute depends of the processors architecture and the OS. -
Platform.runLater messes up my Thread.currentThread().getContextClassLoader()
Hi,
I have a plugin mechanism in my application. The plugins are defines by an interface and are loaded via URLClassLoader. A plugin can also have resources, loaded via ResourceBundle.getBundle.
Whenever a plugin's method is called, I do this, before it is called:
ClassLoader oldLoader = Thread.currentThread().getContextClassLoader();
Thread.currentThread().setContextClassLoader(pluginClassLoaders.get(pluginClass.cast(proxy)));
// Invoke plugin method
Thread.currentThread().setContextClassLoader(oldLoader);
The plugin methods are called in their own thread, that means, when I want to open a window I need to do it on the JavaFX Application Thread with Platform.runLater.
The problem is, that in the run method of the Platform.runLater, my Thread.currentThread().getContextClassLoader() is not my URLClassLoader but the Application Classloader.
Why I need this?
I don't want the plugin developer to always keep in mind, that he has to pass the correct class loader (of his classes) into the ResourceBundle.getBundle method.
Instead I thought I could rely on Thread.currentThread().getContextClassLoader(), which is set in the main application, to load the correct bundle.
It would work, but not if I load the bundle inside the JavaFX Application Thread (but which makes the most sense for UI development).
So my goal was to have a convenient method like:
String getResource(String bundle, String key)
return ResourceBundle.getBundle(bundle).getString(key), Thread.currentThread().getContextClassLoader());
To avoid passing the classloader every time.
Any ideas on this?OK, found the problem.
In data-sources.xml, there is a connection pool and a managed-data-source settings. If I set the data source in there - it works!! Seems these XML tags take preference above the datasource tag.
This is how the data-sources.xml now looks that's been working:
<?xml version = '1.0' standalone = 'yes'?>
<data-sources xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://xmlns.oracle.com/oracleas/schema/data-sources-10_1.xsd" schema-major-version="10" schema-minor-version="1">
<connection-pool name="jdev-connection-pool-MYDB">
<connection-factory factory-class="com.mysql.jdbc.Driver" user="henkie" password="->DataBase_User_recGxQcVfghwCszzy_gfsRgwOrxutL2l" url="jdbc:mysql://localhost/mydb"/>
</connection-pool>
<managed-data-source name="jdev-connection-managed-MYDB" jndi-name="jdbc/MYDBDS" connection-pool-name="jdev-connection-pool-MYDB"/>
</data-sources> -
URG & IMP: How does one stop the Thread.currentThread?
hi,
I want to stop the current thread.
Presently teh code used Thread.currentThread.stop()
However stop() has been deprecated
Thread.currentThread.interrupt() doesnot seem to help.
If I try Thread.currentThread.isAlive() post tehinterrupt, it doesnot work as desired and teh thread is still active...
Any pointers????
We have alreday tried using the boolean volatile varible to stop the thread as recommended by sun and since this is the currentThread, it cannot be assigned to null.
Thanks
Priyahi,
I want to stop the current thread.
Presently teh code used Thread.currentThread.stop()Whyever would a thread want to deliver a stop() to itself.
Did you mean that you wanted to stop() a different thread?
As indicated in the (depreaction) documentation for stop(), using interrupt()
is a better idea. However, that requires you to have a protocol
where the receiver of the interrupt then reacts in an appropriate
manner, i.e. interrupt() can be the basis for cooperative
thread termination; it can't merely replace a stop() call
in an existing application without any other changes.
>
However stop() has been deprecated
Thread.currentThread.interrupt() doesnot seem to
help.
If I try Thread.currentThread.isAlive() post
tehinterrupt, it doesnot work as desired and teh
thread is still active...
Any pointers????
We have alreday tried using the boolean volatile
varible to stop the thread as recommended by sun and
since this is the currentThread, it cannot be
assigned to null.Think about what you are trying to achieve. Did you want
to just do a Throw() out of the current method, with (or
without )a corresponding Catch() in some outer context)
so that the you can unwind in case of an exceptional
condition and have the thread exit?
>
Thanks
Priya -
Thread.currentThread() unique for each server request?
Hello
I have a hosted application in glassfish. When there is a http request I write a file to disk in server machine.
I am just wondering in writer.class can I use Thread.currentThread() as a unique identification for each and every request?
Thank youI am sorry. I made the question wired by adding unnessasary things.
Let me ask it simple, can I replace the singleton class IDpool with a class with a static variable id. like following
IDpool class (singleton and map<thread, id>)
public class IdPool {
protected static IdPool pool = null;
protected static Map<Thread,Long> idmap = new HashMap<Thread,Long>();
public static Map<Thread,Long> getIdMap()
return idmap;
public static IdPool getSingleInstance()
if(IdPool.pool==null)
IdPool.pool = new IdPool();
return IdPool.pool;
public synchronized Long makeNewId(Thread thread)
Long id = Calendar.getInstance().getTimeInMillis();
IdPool.idmap.put(thread,id);
return id;
public synchronized Long getId(Thread thread)
return IdPool.idmap.get(thread);
}replace above with following
class IDClass
public static long ID;
}In request handler class
// make new id
IDClass.ID = 123;In FileWriter.class
// get ID
long id = IDClass.ID;Because for each and every request it starting as a new application. Application means calling for the backend Request handler and file writer program I have made. Those are in a seperate jar file.The same instance of the application never used by two request. And once the request is finished application initialize for that particular request close down.
EJP, thank you very much for your kind attention for this matter. -
Thread.currentThread().getContextClassLoader().getResourceAsStream() bug?
Hello
I have a problem with Thread.currentThread().getContextClassLoader().getResourceAsStream() sporadically returning null when my app is running via JNLP using Win XP/build 1.6.0_20-b02 and tomcat 6-20/JnlpDownLoadServlet.
The code is:
final InputStream resourceStream = Thread.currentThread().getContextClassLoader().getResourceAsStream(name);I have added a map that counts the number of non null streams returned by getResourceAsStream. Here is the output when running with tracing level 5:
cache: Reading Signers from 1024 http://x.x.x.x:8080/MDA/webstart/VTSDBClient-SOK.jar | C:\Users\xxx\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\61\6b90d63d-4feb6af0-1.7-SNAPSHOT-.idx
cache: Read manifest for http://10.10.20.64:8080/MDA/webstart/VTSDBClient-SOK.jar: read=117 full=14269
cache: Reading Signers from 1024 http://x.x.x.x:8080/MDA/webstart/VTSDBClient-SOK.jar | C:\Users\xxx\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\61\6b90d63d-4feb6af0-1.7-SNAPSHOT-.idx
Weird! data/eez-de.shp has been loaded 77 time(s) previously but is now null
Loader is com.sun.jnlp.JNLPClassLoaderSo getResourceAsStream managed to open the file 77 times before it suddenly returns null.
From the trace it looks like it happens when the cache is doing " Reading Signers from 1024 ..." the second time for VTSDBClient-SOK.jar. Could it be related to bug 6911763 (http://bugs.sun.com/view_bug.do?bug_id=6911763)?
What causes the cache to reread the Signers in general and is there a way to provoke it?
Thanks
CarstenJust a tad more info on this.
Each time Thread.currentThread().getContextClassLoader().getResourceAsStream() returns null there is a:
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 10000in the log.
My does does spawn multiple threads that accesses different resources located in the same jar file in the client. Could it be a problem with using Thread.currentThread().getContextClassLoader().getResourceAsStream() from multiple threads and a slow respose from the JNLPDownLoadServlet and some locking scheme used by the JNLP cache?
cache: Reading Signers from 1024 http://x:8080/MDA/webstart/aislayer.jar | C:\Users\x\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\52\5e675934-678dbaa9-1.5-SNAPSHOT-.idx
BinaryFile: trying to figure out how to handle [3] data/eez-dk.shp
cache: Reading Signers from 1024 http://x:8080/MDA/webstart/aislayer.jar | C:\Users\x\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\52\5e675934-678dbaa9-1.5-SNAPSHOT-.idx
BinaryFile: trying to figure out how to handle [3] data/eez-se.shp
cache: Reading Signers from 1024 http://x:8080/MDA/webstart/aislayer.jar | C:\Users\x\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\52\5e675934-678dbaa9-1.5-SNAPSHOT-.idx
BinaryFile: trying to figure out how to handle [3] data/12nm.shp
cache: Reading Signers from 1024 http://x:8080/MDA/webstart/aislayer.jar | C:\Users\x\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\52\5e675934-678dbaa9-1.5-SNAPSHOT-.idx
BinaryFile: trying to figure out how to handle [3] data/eez-pl.shp
cache: Reading Signers from 1024 http://x:8080/MDA/webstart/aislayer.jar | C:\Users\x\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\52\5e675934-678dbaa9-1.5-SNAPSHOT-.idx
BinaryFile: trying to figure out how to handle [3] data/danm_nav.shp
BinaryFile: trying to figure out how to handle [3] data/europ_nav.shp
BinaryFile: trying to figure out how to handle [3] data/eez-de.shp
network: SyncFileAccess.openLock: handled OverlappingFileLockException, remainint TO : 10000 -
Using Thread.currentthread.sleep but not delaying appropriately
Ok, here it goes. Im currently using the thread.sleep method to delay the changing of the text within some labels. I have 3 labels which represent some arrays. I then sort the arrays. Im trying to throw a delay in so that the user can see the changes happen to the array. Although, when I call the wait.millisec(1000) in (the sleep function I threw into its own wait class) it seems that the waiting all happens at the end. I dont see it during the loop to show the arrangement changes within the arrays. I stepped through the code using the debugger, but it doesnt seem to help.
Look in the buttonListener within the FourX class.
* SortTest.java Author:Tim Dudek
This trivial program tests the insertion sort and selection sort
subroutines. The data is then shown graphically.
import javax.swing.JFrame;
import javax.swing.JLabel;
public class SortTest {
final static int ARRAY_SIZE = 10; // Number of items in arrays to be sorted.
// (This has to be 10 or more.)
public static int[] A, B;
public static JLabel lblOrig, lblSS, lblIS;
public static void main(String[] args) {
JFrame frame = new JFrame ("Tim Dudek");
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
FourX display = new FourX();//create the main panel
frame.setSize(450, 320);
frame.getContentPane().add(display);
frame.setVisible(true);
A = new int[ARRAY_SIZE]; // Make an array ints
for (int i = 0; i < A.length; i++){ // Fill array A with random ints.
A[i] = (int)(100*Math.random());
lblOrig.setText(lblOrig.getText() + " " + A);
lblIS.setText(lblIS.getText() + " " + A[i]);
lblSS.setText(lblSS.getText() + " " + A[i]);
B = (int[])A.clone(); // make B an exact copy of A.
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class FourX extends JPanel {
static final long serialVersionUID = 1L; //eclipse echo problem
private JLabel lblO, lblI, lblS;
private JButton sort;
public FourX(){//JLabel lblOrig,JLabel lblSS, JLabel lblIS){
setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
SortTest.lblSS = new JLabel ("");
SortTest.lblOrig = new JLabel ("");
SortTest.lblIS = new JLabel ("");
lblO = new JLabel("Orginal", JTextField.LEFT);
lblI = new JLabel("Insertion Sort", JTextField.LEFT);
lblS = new JLabel("Selection Sort", JTextField.LEFT);
sort = new JButton("Sort");
sort.addActionListener(new buttonListener());
SortTest.lblSS.setFont(new Font("Arial", Font.BOLD, 30));
SortTest.lblSS.setHorizontalAlignment(JTextField.CENTER);
SortTest.lblSS.setBorder(BorderFactory.createLineBorder (Color.RED, 3));
SortTest.lblIS.setFont(new Font("Arial", Font.BOLD, 30));
SortTest.lblIS.setHorizontalAlignment(JTextField.CENTER);
SortTest.lblIS.setBorder(BorderFactory.createLineBorder (Color.BLUE, 3));
SortTest.lblOrig.setFont(new Font("Arial", Font.BOLD, 30));
SortTest.lblOrig.setHorizontalAlignment(JTextField.CENTER);
SortTest.lblOrig.setBorder(BorderFactory.createLineBorder (Color.BLACK, 3));
add(Box.createRigidArea(new Dimension (10, 10)));
add(lblO);
add(SortTest.lblOrig);
add(Box.createRigidArea(new Dimension (10, 10)));
add(lblS);
add(SortTest.lblSS);
add(Box.createRigidArea(new Dimension (10, 10)));
add(lblI);
add(SortTest.lblIS);
add(Box.createRigidArea(new Dimension (10, 10)));
add(sort);
private class buttonListener implements ActionListener{
public void actionPerformed (ActionEvent event){
// sort A into increasing order, using selection sort
for (int lastPlace = SortTest.A.length-1; lastPlace > 0; lastPlace--) {
Wait.milliSec(50);
//Find the largest item among A[0], A[1], ... A[lastPlace],
// and move it into position lastPlace by swapping it with
// the number that is currently in position lastPlace
int maxLoc = 0; // location of largest item seen so far
for (int j = 1; j <= lastPlace; j++) {
if (SortTest.A[j] > SortTest.A[maxLoc])
maxLoc = j; // Now, location j contains the largest item seen
int temp = SortTest.A[maxLoc]; // swap largest item with A[lastPlace]
SortTest.A[maxLoc] = SortTest.A[lastPlace];
SortTest.A[lastPlace] = temp;
Wait.milliSec(100);//<------------ waiting???>
SortTest.lblSS.setText("");
for (int i = 0; i < SortTest.A.length; i++){
SortTest.lblSS.setText(SortTest.lblSS.getText() + " " + SortTest.A[i]);
Wait.oneSec();//<------------ waiting???>
// sort the array A into increasing order
int itemsSorted; // number of items that have been sorted so far
for (itemsSorted = 1; itemsSorted < SortTest.B.length; itemsSorted++) {
// assume that items A[0], A[1], ... A[itemsSorted-1] have
// already been sorted, and insert A[itemsSorted] into the list.
int temp = SortTest.B[itemsSorted]; // the item to be inserted
int loc = itemsSorted - 1;
while (loc >= 0 && SortTest.B[loc] > temp) {
SortTest.B[loc + 1] = SortTest.B[loc];
loc = loc - 1;
SortTest.B[loc + 1] = temp;
Wait.milliSec(100);//<------------ waiting???> SortTest.lblIS.setText("");
for (int i = 0; i < SortTest.B.length; i++){
SortTest.lblIS.setText(SortTest.lblIS.getText() + " " + SortTest.B[i]);
public class Wait {
public static void oneSec() {
try {
Thread.currentThread().sleep(1000);
catch (InterruptedException e) {
e.printStackTrace();
public static void milliSec(long s) {
try {
Thread.currentThread().sleep(s);
catch (InterruptedException e) {
e.printStackTrace();Wow, ok. this is extrodinarily confusing. I read the tutorials, but they're not easy to follow.
So, what I did was at the entry point:
public class SortTest implements Runnable {
final static int ARRAY_SIZE = 10; // Number of items in arrays to be sorted.
// (This has to be 10 or more.)
public static int[] A, B;
public static JLabel lblOrig, lblSS, lblIS;
public static void main(String[] args) {
(new Thread(new SortTest())).start();
public void run(){
JFrame frame = new JFrame ("Tim Dudek");
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
FourX display = new FourX();//create the main panel
frame.setSize(450, 320);
frame.getContentPane().add(display);
frame.setVisible(true);
A = new int[ARRAY_SIZE]; // Make an array ints
for (int i = 0; i < A.length; i++){ // Fill array A with random ints.
A[i] = (int)(100*Math.random());
lblOrig.setText(lblOrig.getText() + " " + A);
lblIS.setText(lblIS.getText() + " " + A[i]);
lblSS.setText(lblSS.getText() + " " + A[i]);
B = (int[])A.clone(); // make B an exact copy of A.
Ok, as I understand, this creates the initial thread to build the gui. Now you suggest that when the user hits "sort" that a second thread be created to handle the sorting routine. From what I understand I can only inherit from one class in java. My buttonListener already implements ActionListener. I obviously cant implement ActionListener and Runnable. Do you have a suggestion? Maybe a link to an example?
I'm pretty lost.
Tim -
Localizion resource problem about *.resx and Thread.CurrentThread.CurrentCulture
Hello all,
I have a strange question. I am building an application which is for US and other localizations
In one project. I create different resources -- it is *.resx file. For example
They are Text.resx and Text.zh-Hans.resx files.
At the start of the application I add the following code
Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture("zh-Hans"); Thread.CurrentThread.CurrentUICulture = CultureInfo.CreateSpecificCulture("zh-Hans");
in the later code, program access the Properties defined in *.resx files for different languages.
Now here is question. The application works in one Win7 box. But it doesn't work in another Win7 box.
In the Win7 box which has problem, the application always displays the English text (which are defined at Text.resx )
It doesn't display the simplified Hans defined in Text.zh-Hans.resx.
I have tried several system settings, but nothing works in that Win7 box.
Does any one has any idea with it?
Thanks
Good luck@startor
I am glad to know you solved this problem and thanks for sharing the solution.
It will be very beneficial for other community members who have the similar questions.
Best Regards,
Kristin
We are trying to better understand customer views on social support experience, so your participation in this interview project would be greatly appreciated if you have time. Thanks for helping make community forums a great place.
Click
HERE to participate the survey. -
Menu and Thread.sleep(5000) or Thread.currentThread.sleep(5000)
Hi,
I am using JMenu and switchable JPanels.
When I click on a MenuItem the follownig code should starts
cards.add(listenPanel, "listenPanel");
cardLayout.show(cards, "listenPanel");
try{
Thread.sleep(5000); //in ms
PlayMP3Thread sound = new PlayMP3Thread("sound/ping.mp3");
} catch(Exception e) {
e.printStackTrace();
}It seems to be what I want to reach, but it does not work the way I want it to.
I would like the Panel to show right away, then wait 5s and then play the sound.
BUT what it does is freez the unfolded menu for 5s, then plays the sound and after that it shows the new Plane.
Can you tell me why this is??This might be what you want
package tjacobs.thread;
import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.concurrent.Semaphore;
import tjacobs.ui.Eyes;
import tjacobs.ui.util.WindowUtilities;
public class ThreadForMultipleAnytimeRuns extends Thread {
private Runnable mRunnable;
private Semaphore mSemaphore;
public ThreadForMultipleAnytimeRuns(Runnable arg0) {
super();
init(arg0);
private void init(Runnable r) {
mRunnable = r;
mSemaphore = new Semaphore(0);
setDaemon(true);
public ThreadForMultipleAnytimeRuns(Runnable arg0, String arg1) {
super(arg1);
init(arg0);
public ThreadForMultipleAnytimeRuns(ThreadGroup arg0, Runnable arg1, String arg2) {
super(arg0, arg2);
init(arg1);
public void run () {
try {
while (!isInterrupted()) {
mSemaphore.acquire();
mRunnable.run();
catch (InterruptedException ex) {}
public void runAgain() {
mSemaphore.release();
public void runAgain(int numTimes) {
mSemaphore.release(numTimes);
public void stopThread() {
interrupt();
public int getSemaphoreCount() {
return mSemaphore.availablePermits();
public Runnable getRunnable() {
return mRunnable;
//The setRunnable method is simply not safe, and
//trying to make it safe is going to effect performance
//Plus I can't really see a gain in being able to set
//The runnable on one of these threads. Just create
//a new one!
public synchronized void setRunnable(Runnable r) {
if (getSemaphoreCount() > 0) {
try {
wait();
catch (InterruptedException ex) {
return;
mRunnable = r;
public static void main(String[] args) {
final Eyes eyes = new Eyes(true);
//eyes.addMouseMotionListener(eyes);
Runnable r = new Runnable() {
public void run() {
eyes.blink();
try {
Thread.sleep(100);
catch(InterruptedException ex) {}
final ThreadForMultipleAnytimeRuns ar = new ThreadForMultipleAnytimeRuns(r);
ar.start();
eyes.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent me) {
ar.runAgain();
eyes.setPreferredSize(new Dimension(60,20));
WindowUtilities.visualize(eyes);
// JFrame jf = new JFrame();
// jf.add(eyes);
// jf.pack();
// jf.setLocation(100,100);
// jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// jf.setVisible(true);
} -
Performance overhead of calling Thread.currentThread().getStackTrace()
All I can see is it is calling native function
private static native StackTraceElement[][] dumpThreads(Thread athread[]);
Just wonder if I call this method for every transaction, will this causing performance issue? Is this method considered slow to execute?How about compare with String concat?
We now having our own transaction framework, at the end of the transaction the module call transaction.start() must call either commit() / close() . If that module doesn't do that, next module cannot start() another transaction. I understand this is not a good design, but this is what this is and I am not the module owner so I can say nothing about that.
However, I would still like to have some checking to see if any the transaction starter forget to commit / close the transaction. I just thought of in method start() I save a copy of stacktrace() element. If the transaction cannot start then I show the printStack() of last saved copy so that I know which module have that problem.
How do you think about that? -
Thread state; "runnable"; what is it mean ?
Hi All,
could somebody please explain:
what does all the thread states exactly mean?
a more specific question:
there is a thread state called "runnable" ....what does this state exactly means?
i mean does it mean this thread is "running" OR is it "about" to run.
OR this thread state means: what it can do, not what it is doing.
Please explain.
thanks, sangitaWrong. A thread in a runnable state may not be running. It could be, but mearly by being in the
Runnable state does not force it to be running. Calling thread.start() schedules the thread to run.
Therefore runnable means it could be running or it could be ready to run. You are using "running" as "using CPU".
I was using "running" in the sense of the Sun's tutorial in pointed to.
From the tutorial:
"After the start method has returned, the thread is "running". Yet, it's somewhat more complex than that. As the previous figure shows, a thread that has been started is actually in the Runnable state. Many computers have a single processor, thus making it impossible to run all "running" threads at the same time. The Java runtime system must implement a scheduling scheme that shares the processor between all "running" threads. (See Understanding Thread Priority for more information about scheduling.) So at any given time, a "running" thread actually may be waiting for its turn in the CPU. " -
Multiple threads access the same method.
Hello,
I have been trying for a long time to find out multiple threads access the shared data.
I have written a sample code, there I my intention is that method has to be accessed
onlny one thread at a time., mean one thread finished the job, then next thread can
access the shared source. But for this code I am not getting the desired out put what I want. But if I am using synchronized block I am getting the output. Please correct where I got mistake. Please see my code.
public class TestThread implements Runnable {
Shared r;
public TestThread() {
r = new Shared();
public static void main(String args[]) {
Thread t1 = new Thread(new TestThread());
Thread t2 = new Thread(new TestThread());
t1.setName("A");
t2.setName("B");
t1.start();
t2.start();
* (non-Javadoc)
* @see java.lang.Runnable#run()
@Override
public void run() {
// TODO Auto-generated method stub
r.count();
class Shared {
public synchronized void count() {
String name = Thread.currentThread().getName();
System.out.println(name + ":accessed...");
try {
for (int i = 0; i < 5; i++) {
System.out.println(name + ": " + i);
} catch (Exception e) {
// TODO: handle exception
}Thanks
Bhanu lakshmi.It depends on what you synchronize. Non-static methods synchronize on the object, so if you're using several objects, you'll be able to call each from their own thread.
Make your method synchronized or use only a single object and see the difference. -
Stopping a Thread in Infinite Loop
I've read several articles on how to stop Threads, and all of them point to using Thread.interrupt(). The problem right now is what happens when the thread is in an infinite loop. For example:
class A implements Runnable
public void run()
while(!Thread.currentThread().isInterrupted())
while(true);
//in other class's main method:
Thread a = new Thread(new A());
a.start();
a.interrupt();The a.interrupt() call only sets the isInterrupted flag in Thread, but it does not terminate the thread as a.stop() would. However, stop() throws a ThreadDeath exception that I would not want to have to deal with. Is there any way to stop this infinite loop thread safely?
Thanks in advance!No need to get snitty. You certainly did not make clear that you are not a newbie at programming. Plenty of newbies who barely have a grasp of the language fundamentals post thread questions here. I thought I did address the question at hand. It seems I misunderstood what you were asking.
The only way to safely stop that inner loop is like so: while (...) {
while (!done) {
}where done is volatile, or all access to it is sychronized on the same lock (meaning you'd sync the !done check above as well).
If you can't do that, and it's stuck at while (true) and you can't modify the body of the inner loop to check done, then you're SOL.
(I suppose it's conceivable that 1.6 or 6.0 or whatever it's called will introduce some new safe way to stop that thread, but I haven't heard anything about it.) -
Thread-safe design pattern for encapsulating Collections?
Hi,
This must be a common problem, but I just can't get my head around it.
Bascially I'm reading in data from a process, and creating/updating data structuers from this data. I've got a whloe bunch of APTProperty objects (each with a name/value) stored in a sychronized HashMap encapsulated by a class called APTProperties. It has methods such as:
addProperty(APTProperty) // puts to hashmap
getProperty(String name) // retreives from hashmap
I also want clients to be able to iterate through all the APTProperties, in a thread safe manner . ie. they aren't responsible for sychronizing on the Map before getting the iterator. (See Collections.synchronizedMap() API docs).
Is there any way of doing this?
Or should I just have a method called
Iterator propertyIterator() which returns the corresponding iterator of the HashMap (but then I can't really make it thread safe).
I'd rather not make the internal HashMap visible to calling clients, if possible, 'cause I don't want people tinkering with it, if you know what I mean.
Hope this makes sense.
KeithIn that case, I think you need to provide your own locking mechanism.
public class APTProperties {
the add, get and remove methods call lock(), executes its own logic, then call unlock()
//your locking mechanism
private Thread owner; //dont need to be volatile due to synchronized access
public synchronized void lock() {
while(owner != null) {
wait();
th = Thread.currentThread();
public synzhronized void unlock() {
if(owner == currentThread()){
owner = null;
notifyAll();
}else {
throw new IllegalMonitorStateException("Thread: "+ Thread.currentThread() + "does not own the lock");
Now you dont gain a lot from this code, since a client has to use it as
objAPTProperties.lock();
Iterator ite = objAPTProperties.propertyIterator();
... do whatever needed
objAPTProperties.unlock();
But if you know how the iterator will be used, you can make the client unaware of the locking mechanism. Lets say, your clients will always go upto the end thru the iterator. In that case, you can use a decorator iterator to handle the locking
public class APTProperties {
public Iterator getThreadSafePropertyIterator() {
private class ThreadSafeIterator implements Iterator {
private iterator itr;
private boolean locked;
private boolean doneIterating;
public ThreadSafeIterator(Iterator itr){
this.itr = itr;
public boolean hasNext() {
return doneIterating ? false : itr.hasNext();
public Object next() {
lockAsNecessary();
Object obj = itr.next();
unlockAsNecessary();
return obj;
public void remove() {
lockAsNecessary();
itr.remove();
unlockAsNecessary();
private void lockAsNecessary() {
if(!locked) {
lock();
locked = true;
private void unlcokAsNecessary() {
if(!hasNext()) {
unlock();
doneIterating = true;
}//APTProperties ends
The code is right out of my head, so it may have some logic problem, but the basic idea should work. -
Thread safe RMI.
My RMI server provides clients with the ability to CRUD data but in order to manage concurrency I did the following.
1stly I would like to understand correctly the issues of RMI server objects....
It is my understanding that RMI server can cater for eg 100 clients by spawning 100 threads at random for each client. This process is not managed (thread wise) and the result is that 20 clients wishing to update record A can do so at will? Various steps can be taken from what I gather...
a) Synchronise (expensive)
b) implement a lock manager.
The step I have taken is include a lock manager and I have ensured that all locking an unlocking occur in a singleton server object that manages all sensitive data CRUD operations. Now I use a lock manager but I would like to know what happens if for eg the 1st RMI client dies and has its thread blocking
all other threads from locking the same record? Does the thread die with the client or is there a counter measure for this? The obvious answer that comes to mind is Object.wait() inside the lock manager?
The reason I ask was that because all of the locking occurs in a single method call in the Network
Server's JVM, so is there a need to worry about the RMI connection dying during the middle the locking operation.
Edited by: Yucca on May 23, 2009 8:14 PM/*
* @(#)LockManager.java
* Version 1.0.0
* 27/03/2009
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Logger;
import java.util.ResourceBundle;
class LockManager {
* The <code>Map</code> containing all the record number keys of currently
* locked records that pair with the cookie value assigned to them when they
* are initially locked.
private static Map<Integer, Long> currentlyLockedMap =
new HashMap<Integer, Long>();
private static final Logger LOG = Logger.getLogger("project.db");
* Locks a record so that it can only be updated or deleted by this client.
* Returned value is a <code>long</code> that is the cookie value that must
* be used when the record is unlocked, updated, or deleted.
* If the specified record is already locked by a different client, then the
* current thread gives up the CPU and consumes no CPU cycles until the
* record is unlocked.
* @param recNo the assigned primary key of the record
* to be locked for an operation.
* @param data a <code>Data</code> instance used to
* check if the record exists before
* attempting the lock operation.
* @return A <code>long</code> containing the
* cookie value that must be used when the
* record is unlocked.
* @throws RecordNotFoundException if specified record does not exist or if
* specified record is marked as deleted
* in the database file.
long lock(int recNo, DB data) throws RecordNotFoundException {
LOG.entering(this.getClass().getName(), "lock", recNo);
synchronized (currentlyLockedMap) {
try {
while (currentlyLockedMap.containsKey(recNo)
&& currentlyLockedMap.get(recNo)
!= Thread.currentThread().getId()) {
currentlyLockedMap.wait();
// Check if record exists.
data.read(recNo);
long cookie = Thread.currentThread().getId();
currentlyLockedMap.put(recNo, cookie);
LOG.fine("Thread " + Thread.currentThread().getName()
+ "got Lock for " + recNo);
LOG.fine("Locked record count = " + currentlyLockedMap.size());
LOG.exiting(this.getClass().getName(), "lock", true);
return cookie;
} catch (InterruptedException ie) {
throw new SystemException("Unable to lock", ie);
* Releases the lock on a record. The cookie must be the cookie returned
* when the record was locked.
* @param recNo the assigned primary key of the record
* to be unlocked after an operation.
* @param cookie the cookie returned when the record was
* locked.
* @throws RecordNotFoundException if specified record does not exist or if
* specified record is marked as deleted
* in the database file.
* @throws SecurityException if the record is locked with a cookie
* other than cookie.
void unlock(int recNo, long cookie) throws RecordNotFoundException,
SecurityException {
LOG.entering(this.getClass().getName(), "unlock",
new Object[] { recNo, cookie });
synchronized (currentlyLockedMap) {
checkLock(recNo, cookie);
currentlyLockedMap.remove(recNo);
LOG.fine("released lock for " + recNo);
currentlyLockedMap.notifyAll();
LOG.exiting(this.getClass().getName(), "unlock");
* Checks if the given record is locked before doing any modification or
* unlocking for the record.
* <p/>
* Checks the <code>Map</code> of record number keys and cookie values
* to see if it contains the given record number.
* @param recNo the assigned primary key of the record
* to be checked if it is locked.
* @param lockCookie the cookie returned when the record was
* initially locked.
* @throws SecurityException if no lock exists for the record or if
* the record has been locked with a
* different cookie.
void checkLock(int recNo, long lockCookie) throws SecurityException {
LOG.entering(this.getClass().getName(), "checkLock",
new Object[] { recNo, lockCookie });
// Check if record has been locked
if (!currentlyLockedMap.containsKey(recNo)) {
throw new SecurityException(ResourceBundle.getBundle(
"resources.ErrorMessageBundle").getString(
"lockNotAppliedKey"));
// Check if record has been locked by different cookie.
if (currentlyLockedMap.get(recNo) != lockCookie) {
throw new SecurityException(ResourceBundle.getBundle(
"resources.ErrorMessageBundle").getString(
"notLockOwnerKey"));
LOG.exiting(this.getClass().getName(), "checkLock");
}Edited by: Yucca on May 23, 2009 8:16 PM
Edited by: Yucca on May 23, 2009 8:18 PMIt is my understanding that RMI server can cater for eg 100 clients by spawning 100 threads at random for each client.No. It spawns a new thread for every new connection. At the client end, RMI makes a new connection for every call unless it can find an idle connection to the same host that is less than 15 seconds old. So if the client is doing concurrent calls there will be concurrent threads at the server for that client.
This process is not managed (thread wise)'Managed' meaning what?
the result is that 20 clients wishing to update record A can do so at will?The result is that an RMI server is not thread safe unless you make it so.
a) Synchronise (expensive)Compared to a database update the cost of synchronization is trivial.
b) implement a lock manager. The database should already have one of those, and so does java.util.concurrent. Don't write your own. Personally I would just syncrhonize around the database calls.
what happens if for eg the 1st RMI client dies and has its thread(a) the client doesn't have a thread, see above. The call has a thread.
(b) at the server, the call will execute, regardless of the state of the client, until it is time to write the result back to the client, at which point the write will encounter an IOException of some description and the thread will exit.
blocking all other threads from locking the same record?That can't happen unless you foul up your concurrency management.
Does the thread die with the clientIt dies with the call.
is there a need to worry about the RMI connection dying during the middle the locking operation.The server JVM won't notice until it is time to write the call result back, see above.
Maybe you are looking for
-
Cannot click in the Search field
I cannot click in the Search field and perform a search in the Store.
-
Cannot drag & drop clip in Home Video of itune 11.1.3.8
It has been a few months since I last drop video clip onto the itune and then transfer it to my iphone by clicking the Sync button. Today, when I tried to drop more clips into my Home Videos under the Movies to transfer to my iphone, I NO LONGER able
-
IMessage won't allow me to message anyone
When I try to use iMessage on my MacBook, I cannot message anyone. I get the error message that "(phone number) is not registered with iMessage." I can iMessage the same person using my phone, but for some reason it will not work on my computer. I ha
-
Gl code combination segments description
Hi all i am feeling very difficulty to retrieve the gl code combination segments description. Can any one help on this by giving the query Advance Thanks
-
Parameter in Designer - Related to Authorisation
Hi Friends, Can u please help with my request. Lets say user has access to only one country Germany according to the roles assigned to him. When user accessing some BW reports, in entry variable screen the country Germany is automatically filtered b