Java FX task daemon thread

Hello,
I'm working on a large scale GUI and running in to OOMs. Looking at the threads, there are hundreds of them sitting around named Java FX task daemon thread.
Daemon Thread [Java FX task daemon thread] (Running)
                                Daemon Thread [Java FX task daemon thread] (Suspended)
                                                Unsafe.park(boolean, long) line: not available [native method]
                                                LockSupport.park(Object) line: 158
                                                AbstractQueuedSynchronizer$ConditionObject.await() line: 1987
                                                DelayQueue<E>.take() line: 160
                                                ScheduledThreadPoolExecutor$DelayedWorkQueue.take() line: 609
                                                ScheduledThreadPoolExecutor$DelayedWorkQueue.take() line: 602
                                                ScheduledThreadPoolExecutor(ThreadPoolExecutor).getTask() line: 947
                                                ThreadPoolExecutor$Worker.run() line: 907
                                                Thread.run() line: 662    Can anyone shed some light on what is starting these threads?

I had similar issues with a server running on XP, where it kept dying randomly with no problems.
I tracked down what was happening by getting the exit value of the java process - which may give you information regarding what happened to the process.
For example, if CTRL+C was pressed you get a value of 130 returned in the Linux environment. Using this error information I found out why my server kept dying (which was the XP telnet window was sending dodgy key presses to the window the server was running in).
The exit code of a process is available after it exits via $status in Unix or %errorlevel% in a PC .bat file.

Similar Messages

What is a daemon thread in java ?

What is a daemon thread in java ? Explain with a small example.

Any thread marked as a daemon. There is nothing special about it. The only intersting thing is that the Java VM terminates if no non-daemon thread is running. So you usually use a daemon thread for bookkeeping tasks, so that this thread doesn't prevent the VM from successfully terminating.

Cannot start JavaFX Task using Thread.start()

Well I am currently studying JavaFX and as a total beginner(but not in Java) I started reading the official tutorials in Java and I'm currently studying Concurrency in JavaFX. and I tried to create my first JavaFx Task Object and start it. This what I have tried so far
package concurrency;
import javafx.concurrent.Task;
public class JavaTaskClass {
      * @param args
     public static void main(String[] args) {
          //create task object
          Task<Integer> task = new Task<Integer>(){
               @Override
               protected Integer call() throws Exception{
                    System.out.println("Background task started...");
                    int iterations;
                    for(iterations = 0; iterations < 10000; iterations++){
                         if(isCancelled()){
                              break;
                         System.out.println("Iteration " + iterations);
                         Thread.sleep(3000);
                    return iterations;
          //start the background task
          Thread th = new Thread(task);
          th.setDaemon(true);
          System.out.println("Starting background task...");
          th.start();
but the task doesn't start. I don't see any messages in my console. Is there something I missed?
Edited by: 979420 on Jan 1, 2013 10:02 PM
Edited by: 979420 on Jan 1, 2013 10:02 PM
Edited by: 979420 on Jan 1, 2013 10:03 PM
Edited by: 979420 on Jan 1, 2013 10:49 PM

Tasks are meant to be run in the context of a JavaFX application, like in the example below:
import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import java.io.IOException;
public class TaskApp extends Application {
public static void main(String[] args) { launch(args); }
@Override public void start(final Stage stage) throws IOException {
    //create task object
    Task<Integer> task = new Task<Integer>(){
      @Override
      protected Integer call() throws Exception{
        System.out.println("Background task started...");
        int iterations;
        for(iterations = 0; iterations < 10000; iterations++){
          if(isCancelled()){
            break;
          System.out.println("Iteration " + iterations);
          Thread.sleep(3000);
        return iterations;
    //start the background task
    Thread th = new Thread(task);
    th.setDaemon(true);
    System.out.println("Starting background task...");
    th.start();
    stage.setScene(new Scene(new StackPane(), 200, 100, Color.BLANCHEDALMOND));
    stage.show();
}Also your code was setting the task thread as a daemon thread. The Java Virtual Machine exits when the only threads running are all daemon threads. So once your main routine finished (which would be really quickly), the program would just exit without doing anything much. Note that, in your example, even if you made the Task thread a non-daemon thread, it still doesn't work (likely because the Task class has some reliance on the JavaFX system being initialized). For your simple background process you could skip Task and just use a Runnable or a Callable (which doesn't require JavaFX and hence would work in a non-daemon thread invoked from main), but I guess it's just an experiment.

I wanna the java run task when the machine be relative idle, how to do it?

for my machine may be a little busy,
i wanna the java programe will run the main task when the cpu be a little idle.
how can i get the cpu running infomation?

or how about giving the thread the lowest possible
priority...?Even if you do that, I think the thread set with the
lowest priority will contend for the cpu where as a
daemon will not.
daemon threads have nothing to do with the fact that they will run when CPU is idle.
read the specs for JVM and don't mislead others.

Thread pool of daemon threads?

If I create a Thread, it can be made a daemon thread by invoking setDaemon(true). But what if I create a thread pool via java.util.concurrent.Executors.newFixedThreadPool(NTHREADS)? How can those threads be made daemon threads?
CBy

Thanks Joachim! I didn't know that the newFixedThreadPool method was overloaded.

Daemon thread still alive when the environment is closed

I'm using the replication framework with the Java API in an OSGi container (equinox). I notice that when I'm closing the environment there is a deamon thread still alive. Each time I start a new replication environment and shut it down, one more daemon thread is added (and still running).
Is there a way to close the replication framework and all their associated threads?
I'm using BDB 4.7.25 - windows
thanks
dong

Hi Dong,
I don't know of a way to force the removal of the daemon thread(s).
I believe that the thread is actually gone - as long as you are closing down the environment cleanly. The alternative to using daemon threads is to ensure that DetachCurrentThread is called by the JNI layer for each thread. Given the way the Berkeley DB Java API is implemented, that is not feasible.
Are the additional threads causing issues?
Regards,
Alex

What is a daemon thread?

hi all,
can somebody plz tell me what is daemon thread and what is the difference between daemon thread a user thread. thanx in advance..

Daemons are background programs that run all the time
during up-time, ready to do something that may be
required at any point. These are NOT limited to the
JVM, but the concept is mirrored in teh ability to
set a java thread as daemon, as the JVM is just that:
a Virtual Machine that mimics an environment.
Correspondingly OSs have daemon processes (called
d services on windows) e.g. for printing. Calling
Thread.setDaemon() will I believe mark the thread as
to not be destroyed until VM shutdown, and will not
itself stop shutdown of the VM if it is still running.Maybe I got confused by all those nots but if the only threads running are daemon
threads, the VM is allowed to stop; I made that mistake myself several times.
This is what I ripped from the API docs:
The Java Virtual Machine continues to execute threads until either of the following occurs:
- The exit method of class Runtime has been called and the security manager has permitted the exit operation to take place.
- All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method.
It's the "continues to execute until' ... 'all threads that are *not* daemon threads
have died" part. They should have worded that a bit less cryptic ;-)
kind regards,
Jos
ps. First I thought daemon threads run under your bed while drooling sometimes ;-)

Issue with Java Embedding task in BPEL

Newbe: i have java embedded task in my bpel process which returns one variable(Written java code in editor as it is only 2 lines of code). when i tried to deploy this i am getting the following compiler error in Jdeveloper
Error(36,39): Failed to compile bpel generated classes.
failure to compile the generated BPEL classes for BPEL process "BPELSampleProcess" of composite "default/BpelSampleProj!1.4"
The class path setting is incorrect.
Ensure that the class path is set correctly. If this happens on the server side, verify that the custom classes or jars which this BPEL process is depending on are deployed correctly. Also verify that the run time is using the same release/version.
please suggest me what are the jars needed and where to be placed.

Try this
Random randomGenerator = new Random();
int randomInt = randomGenerator.nextInt(100);
setVariableData("outputVariable","payload","/client:BPEL_Process/client:result",randomInt);
Delete this line public class ChSam
Edited by: KrishnaChaitanya on Nov 25, 2010 9:30 PM

How to use a thread as daemon thread

In multithreading i have undergone through daemon thread concepts and its mentioned as low priority thread which runs in the background of garbage collection.
My query is how to make the thread daemon thread r we going to use thread priorities here.
Can anyone demonstrate with an example reg this. I will be very much thankful to them.

In general, threads that run application code are not daemon threads, and threads that run system code are daemon threads,so the daemon attribute is queried using the isDaemon() method; it is set using the setDaemon() method.....

Java.lang.IllegalMonitorStateException: current thread not owner

Hello,
my program runs an exe that doesn't return a zero when it's finished, therefore, I can't use a waitFor().
To solve this problem i look at the length of the file which has to be manipulated by this exe every 200ms and see whether it's length stopped changing. This should mean it's job is done...
But using this code:
public void run(String filename)
          System.out.println("start runtime");
          Runtime rt = Runtime.getRuntime();
          String[] callAndArgs = { "lssvmFILE.exe", filename };
          try
               Process child = rt.exec(callAndArgs);
               child.wait(200);
               filesize = 0;
               while(filesize != file.length())                            {
                    filesize = file.length();
                    child.wait(200);
               //child.waitFor();
               System.out.println("Process exit code is:   " + child.exitValue());
          catch(IOException e)
          {     System.err.println( "IOException starting process!");}
          catch(InterruptedException e)
          {     System.err.println( "Interrupted waiting for process!");}
          System.out.println("end run");
     }i get this on my System.out:
Exception occurred during event dispatching:
java.lang.IllegalMonitorStateException: current thread not owner
        at java.lang.Object.wait(Native Method)
        at LssvmFile.run(LssvmFile.java:292)
        at LssvmFile.start(LssvmFile.java:189)
        at GUI.actionPerformed(GUI.java:137)
        at java.awt.Button.processActionEvent(Button.java:329)
        at java.awt.Button.processEvent(Button.java:302)
        at java.awt.Component.dispatchEventImpl(Component.java:2593)
        at java.awt.Component.dispatchEvent(Component.java:2497)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:339)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:131)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:98)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:85)

Here's the code:
I already found out that the sleep function indeed caused this exe to run so slow. It seems that everything stops when sleep is used. By setting the delay to 2ms the duration is satisfactory (some seconds).
I also tried skipping the sleep and just using a while, but that ended in an endless loop. Setting the delay to 1ms lead to a stop when the filelength was 0 (i guess that was on the moment that the exe cleared the file and prepared to write) so it seems to me that 2ms is quite a good trade off.
this part of the code is preceeded by writing the data to the file and afterwards the new data will be read in again...
     //Close the stream
          outFileStream.close();
     //Run lssvmFILE.exe to compute alpha & b
          long originalfilesize = file.length();
          run(filename);
          //wait untill job done
          Thread thread = new Thread();
          long filesize = file.length();
          try{thread.sleep(2);}
          catch(InterruptedException e){};
          while(filesize != file.length() || originalfilesize ==file.length())
               filesize = file.length();
               try{thread.sleep(2);}
               catch(InterruptedException e){};
     //Set up Instream (read from file)
     //----------------------Bedankt!
Bart

JNI communiction using a Java and a C++ Thread

Hi,
My purpose is to run a Java and a C++ thread parallel.
The C++ thread receives events from a hardware. Getting an event it should put this (for testing it is just a String ) to a Java method (there the events will be collected in a vector).
The Java thread should compute these vector step by step when it is scheduled.
Therefore I have a Java Thread that invokes a native method.
This C++ method
1. stores a refernece to the JavaVM in a global var (using env->getJavaVM ),
2. stores the object (given by JNICall) in a global var (reference to the calling java object),
3. creates an object dynamically (this implements a Runnable C++ Interface needed for my Thread structure)
4. and creates (dynamically) and starts a C++ Thread ( that uses the Win API ) giving it the former created object as parameter.
Following the C++ thread uses the former stored global JavaVM to get a JNIEnv. It also uses the global stored object.
After this I prepare for executing a callback to Java, e.g. AttachCurrentThread, GetObjectClass, GetMethodID and so on. Finally I sucessfully start some callbacks to Java (in the while loop of the thread).
Now here is my Problem:
The described way only works for a few calls and then raises an error. "java.exe hat ein Problem festgestellt und muss beendet werden." (german os) (In english it should be: "java.exe has detected a problem and has to be determined").
What is wrong with my idea. It is something with the scope of my dynammically created objects? If have no idea anymore.
Here the source code (C++ part):
#include <jni.h>
#include "benchmark.h"
#include "bench.h"
#include "canMessage.h"
JavaVM *jvm;
jobject javaObject;
JNIEXPORT void JNICALL Java_Benchmark_startBench(JNIEnv *env, jobject obj, jobject obj2){
     env->GetJavaVM(&jvm);
     javaObject = obj2;
     cout << "\n C++ Starting benchmark\n\n";
     Benchmark *bm = new Benchmark();
     Thread *thread = new Thread(bm);
     thread->start();
     //thread->join(); //uncomment this there will be no error but also
                                     // no java thread doing it's job
Benchmark::Benchmark(): _continue(false) {
Benchmark::~Benchmark(){
unsigned long Benchmark::run(){
     _continue = true;
     JNIEnv *jniEnv;
        jvm->AttachCurrentThread((void **)&jniEnv, NULL);
        jclass javaClass = jniEnv->GetObjectClass(javaObject);
     if(javaClass == NULL){
          cout << "--> Error: javaClass is null";
     jmethodID methodId = jniEnv->GetMethodID(javaClass, "addMessage", "(Ljava/lang/String;)V");
     if(methodId == NULL){
          cout << "--> Error: methodId is null";
     string str ("This is a test text.");
     const char *cStr = str.c_str();
     jstring javaString = jniEnv->NewStringUTF(cStr);
     jniEnv->CallVoidMethod(javaObject, methodId, javaString );
     int i_loopCount = 0;
     while(_continue){
          i_loopCount++;
          cout << i_loopCount << " C++ runing\n";
          jniEnv->MonitorEnter(javaObject);
          jniEnv->CallVoidMethod(javaObject, methodId, javaString );
          jniEnv->MonitorExit(javaObject);
          canMessage = new CANMessage();
          delete canMessage;
          canMessage = NULL;
     return 0;
void Benchmark::stop(){
     _continue = false;
}Is there a better and more elegant way to solve my problem?
Thanks!

At
http://codeproject.com/cpp/OOJNIUse.asp
http://www.simtel.net/product.php[id]93174[sekid]0[SiteID]simtel.net
http://www.simtel.net/product.php[id]94368[sekid]0[SiteID]simtel.net
you will find examples how to implement Java Interface in JNI C++ without Java coding.
At
http://www.simtel.net/product.php[id]95126[sekid]0[SiteID]simtel.net
you can get pure JNI interface for DOTNET.

Daemon Threads

Hi, what I want is to connect from a daemon thread to Ldap, if I set the thread to daemon=false it works, if I set it to daemon=treu; it does'nt work anymore.
Thanks.

The problem was in fact when I was trying to wrote to file, and not the connection to Ldap. When the thread was set to daemon=false it worked, and I could see that the connection to Ldap was working, but when it was set to daemon=true, the thread couldn't write t the file and I thought that the connection was the problem. Anyway, thanks, the problem is solved now.

Daemon Threads: Can you explain this behaviour

Hey All,
Please refer to code segment given below. As per the defination of Daemon threads it should terminate when all other user threads die. In this case it should terminate when main thread ends as thread2 has not been initiated yet.
The result is not consistent. We get the expected output sometimes, whereas sometimes program goes in to an infinite loop and other times excutes a few lines of thread2 and then quits.
Can someone explain this?
Thank you
Vidur Gupta
class simpleThread extends Thread
     public void run()
          System.out.println("Thread 1 daemon starts");
          babyThread thread2 = new babyThread(); //Thread2 created
          thread2.setDaemon(false); //Thread2 daemon=false
          thread2.start();
          System.out.println("Thread 1 daemon status= "+ this.isDaemon());
          System.out.println("Thread 1 ends"); //thread1 ends
class babyThread extends Thread
     public void run()
          System.out.println("Thread 2 starts");
          while(true) //Thread2 goes in to an infinite loop
          System.out.println("Thread 2 daemon status= "+ this.isDaemon());
public class daemon
     public static void main(String[] args) //Main
          int i=0;
          simpleThread thread1= new simpleThread(); //Create thread1
          thread1.setDaemon(true); //Set Thread1 as Daemon
          thread1.start();
          while(i<1000000)
               i++;
          System.out.println("Thread Main ends"); //Main ends
}

It's not clear what behavior you expect, or what behavior you're observing, but here's what I would expect to happen:
thread1.start() is called.
After that, either of two things could happen:
1) the main thread could go into your very short spinlock counting up to 1000000
OR
2) thread1 starts running
You can't predict or control which one of those happens, and it may be that on successive runs of your program, one happens sometimes and the other one happens other times.
At some point, you'll get to where the main thread dies. If the only other thread that has been started is thread1, then, since it's a deamon, the program will die.
However, it may be that sometimes that happens, and other times, thread1 gets enough CPU time to call thread2.start(). You may not see any output from thread2 or see the ""Thread 1 daemon status" output that comes right after t2.start() before main ends, but if t2 has been started, then you've got another non-deamon.
Bottom line: Whether or not there's an additional non-deamon besides main depends on how the scheduler happens to schedule your threads, and you should not expect that to be consistent or predictable.

Can anyone tell daemon thread in simple words with an example

can anyone tell Daemon thread in simple words (i don't understand high level language)with an example

He reminds me of a candidate I had the ... priviledge? ... of interviewing for a web developer position not too long ago. I asked him to "reverse the characters in a string, i.e. star = rats" using his language of choice. He stands, walks to the white-board and starts to write some stuff. At that time, I turned to my boss and we start making comments to each other about the guys resume and discussing some of our current workload, giving him time to work this code out on the board. A few minutes (5 - 10) go by and I glance up to see that he has written a single line of code (and that his hands are covered in dry erase marker from having scrubbed multiple attempts off the board). His code (I believe it as a stab at either php or javascript) read:
"reverse_string('star');"
I looked at my boss, he looked at me ... we both blinked a couple of times and then I explained, "no - I need you to implement the reverse_string method. I want you to write the code that does the actual reversing."
"Oh. Yeah, I can't do that."

Displaying both ABAP webdynpro and Java Webdynpro tasks in the UWL

Hi,
We have two an issue when trying to get the UWL to process two different types of workflow tasks : ABAP webdynpro and Java webdynpro.
Examples of these tasks are:
TS12300097 u2013 LeaveRequestApprover u2013 Java Webdynpro
TS17900100 - ASR_PROCESS_EXECUTE u2013 ABAP webdynpro
We have two backend systems configured
SAP_ECC_Financials u2013 This has the WAS host pointing to the java stack (xxx:50000)
SAP_ECC_Workflow u2013 This has the WAS host pointing to the ABAP stack (xxx.80xx)
In transaction SWFVISU all the tasks which use Java webdynpro have been configured to use the u2018Javau2019system (SAP_ECC_Financials) using the SYSTEM_ALIAS parameter
In the UWL configuration the system SAP_ECC_Workflow has been registered
In addition to this all u2018Javau2019 tasks have had an extra UWl config XML created to ensure that the SYSTEM_ALIAS is set to SAP_ECC_Financials
The system SAP_ECC_Workflow has been re-registered
The UWL cache has been cleared
However when we try to launch the java webdynpro tasks the system is trying to access the ABAP stack (It is still trying to access the Web AS location for the system SAP_ECC_Workflow even though the system alias was specified as SAP_ECC_Financials )
The ABAP webdynpro tasks (in this case a HCM process and form) are launched correctly
If we try the reverse (i.e register the Java system SAP_ECC_Financials and change the SYSTEM_ALIAS parameter for the ABAP webdynpro tasks to system SAP_ECC_Workflow) then the reverse happens. The java tasks can be launched and the ABAP tasks cannot.
Does anyone have a solution to this problem. Surely other people have implemented both ABAP and Java webdynpro workflows?
Any help much appreciated
Andrew

Thanks a lot for all your replies..
The workitem type registration has been done already, but still it doesn't work..
But here is the actual problem...
There is a link 'Execute Workitem' in the inbox of the approver, or the second level manager...
In the leave application, when we click on this link it is taking to the portal as the task is the Webdynpro Java application task. Whereas, when using ABAP webdynpro application task, it is taking to R/3 - which means that the user cannot access this link without R/3 access. The users are given only portal access, they don't have access to backend R/3.
The requirement is that the link has to take the user to portal directly instead of R/3 - i.e it should ask only for the portal id and password.
Since it was working fine with leave application, I changed the task to Java webdynpro task, but I think the Java Webdynpro application is not deployed in the server.
Please can anybody suggest.
Best Regards,
Sushmitha

Java FX task daemon thread

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