Could you let me know the reason for this error in SWT
"org.eclipse.swt.SWTException" Invalid Thread access ?
And How to fix such errors.
It happens when you try to act upon an interface item from a thread that's not the UI thread.
To run a code on the UI thread you have to use a Runnable and ask the display thread to run it. This way:
Display.getDefault().syncExec( new Runnable() {
#Override
public void run() {
// Do your job here
}
} );
As stated by the syncExec method javadoc,
the thread which calls this method is suspended until the runnable completes.
Also, you might check the asyncExec method.
In SWT you can access GUI resources only from the display thread. For example when setting the text in a org.eclipse.swt.widgets.Text control you must already be in the display thread or call
final Text text = ...;
Display.getCurrent().syncExec(new Runnable() {
#Override
public void run() {
text.setText("test");
}
});
Related
I am trying to write a code that will make things appear on the screen at predetermined but irregular intervals using javafx. I tried to use a timer (java.util, not javax.swing) but it turns out you can't change anything in the application if you are working from a separate thread.(Like a Timer) Can anyone tell me how I could get a Timer to interact with the application if they are both separate threads?
You don't need java.util.Timer or java.util.concurrent.ScheduledExecutorService to schedule future actions on the JavaFX application thread. You can use JavaFX Timeline as a timer:
new Timeline(new KeyFrame(
Duration.millis(2500),
ae -> doSomething()))
.play();
Alternatively, you can use a convenience method from ReactFX:
FxTimer.runLater(
Duration.ofMillis(2500),
() -> doSomething());
Note that you don't need to wrap the action in Platform.runLater, because it is already executed on the JavaFX application thread.
berry120 answer works with java.util.Timer too so you can do
Timer timer = new java.util.Timer();
timer.schedule(new TimerTask() {
public void run() {
Platform.runLater(new Runnable() {
public void run() {
label.update();
javafxcomponent.doSomething();
}
});
}
}, delay, period);
I used this and it works perfectly
If you touch any JavaFX component you must do so from the Platform thread (which is essentially the event dispatch thread for JavaFX.) You do this easily by calling Platform.runLater(). So, for instance, it's perfectly safe to do this:
new Thread() {
public void run() {
//Do some stuff in another thread
Platform.runLater(new Runnable() {
public void run() {
label.update();
javafxcomponent.doSomething();
}
});
}
}.start();
I have a problem while working with JavaFX and Threads. Basically I have two options: working with Tasks or Platform.runLater. As I understand Platform.runLater should be used for simple/short tasks, and Task for the longer ones. However, I cannot use any of them.
When I call Thread, it has to pop up a captcha dialog in a middle of task. While using Task, it ignores my request to show new dialog... It does not let me to create a new stage.
On the other hand, when I use Platform.runLater, it lets me show a dialog, however, the program's main window freezes until the pop up dialog is showed.
I need any kind of solution for this. If anyone knows how to deal with this or had some similar experience and found a solution I am looking forward to hearing from you!
As puce says, you have to use Task or Service for the things that you need to do in background. And Platform.runLater to do things in the JavaFX Application thread from the background thread.
You have to synchronize them, and one of the ways to do that is using the class CountDownLatch.
Here is an example:
Service<Void> service = new Service<Void>() {
#Override
protected Task<Void> createTask() {
return new Task<Void>() {
#Override
protected Void call() throws Exception {
//Background work
final CountDownLatch latch = new CountDownLatch(1);
Platform.runLater(new Runnable() {
#Override
public void run() {
try{
//FX Stuff done here
}finally{
latch.countDown();
}
}
});
latch.await();
//Keep with the background work
return null;
}
};
}
};
service.start();
Use a Worker (Task, Service) from the JavaFX Application thread if you want to do something in the background.
http://docs.oracle.com/javafx/2/api/javafx/concurrent/package-summary.html
Use Platform.runLater from a background thread if you want to do something on the JavaFX Application thread.
http://docs.oracle.com/javafx/2/api/javafx/application/Platform.html#runLater%28java.lang.Runnable%29
It's too late to answer but for those who have the error, here is the solution XD
You can use one Thread.
Use the lambda expression for the runnable in the thread and the runlater.
Thread t = new Thread(() -> {
//Here write all actions that you want execute on background
Platform.runLater(() -> {
//Here the actions that use the gui where is finished the actions on background.
});
});
t.start();
You can user directly this code
Don't forget you can't send non-final variable in thread .
you can send final variable in thread
//final String me="ddddd";
new Thread(new Runnable() {
#Override
public void run() {
// me = me + "eee";
//...Your code....
}
}).start();
Use in
your code
try/catch
Questions about threads are in no shortage, I know, but I can't seem to find a "full" example of a thread doing http work and then coming back to update the UI.
I basically call a few web services upon app launch. I obviously don't want to freeze the UI so I would want to use a separate thread, right? I have found a bunch of examples online on how to get a new thread to perform some task. But I haven't yet found one that shows how to actually update the UI when the thread's task is done.
How do I know when the web service thread is done? Is there a callback method? Can I access the UI from this callback method if one exists.
Edit: (Here is some code)
//The activate method is called whenever my application gains focus.
public void activate(){
DoSomething wsThread = new DoSomething();
wsThread.start();
}
public void wsCallBack()
{
myTabScreen.add(new ButtonField("Callback called"));
}
public class DoSomething extends Thread
{
public void run()
{
try
{
wsCallBack();
}
catch(Exception e)
{
}
}
}
Very simple. But it never creates the button.
Any ideas?
Thanks a lot.
You can set up a "callback" system to notify the UI when the threads complete. Have a class that extends Thread and pass to it a reference of the class that should be called at the end. If you have a list of such classes that needs to be notified create a Vector on the Thread implementation to hold them. Override the run function and after doing everything you need to do simply call a method on the UI class (iterating through the vector if needed). So your classes may look like:
public class commThread extends Thread{
MyUIClass callbackObj;
public commThread(MyUIClass myUiClass){
callbackObj = myUiClass;
}
public void run(){
//do stuff
callbackObj.callback();
}
}
and your UI class:
public MyUIClass{
public void callback(){
//refresh the UI
}
}
Of course if you have multiple threads running at the same time and calling the same UI object make sure to synchronize the callback method.
Hope this helps!
I am having an eclipse View. Inside the view I added a Table. Now I am calling a thread from run method of the view using asyncExec.
My View class is like -
public class SampleViewAction implements IWorkbenchWindowActionDelegate{
Thread t;
int Count;
#Override
public void run(IAction arg0) {
}
}
Now I added a thread like this -
PlatformUI.getWorkbench().getDisplay().asyncExec(new Runnable() {
#Override
public void run() {
new UDPReadThread();
}
});
Where UDPReadThread is a class extends a thread where in UDPReadThread 's constructor I started the thread.
But I am getting invalid Thread exception.
How to resolve the issue.
Similar to AWT and the EventDispatchThread, SWT must process everything in the UI thread.
Your SampleViewAction is run on the UI thread already, in response to a menu or tool item selection.
It looks like your problem comes from then using an asyncExec(*) which will post the runnable to be run on the UI thread (which delays it), and starting a new thread from that asyncExec Runnable. You may as well simply start your thread, and get rid of that asyncExec.
Your UDPReadThread is not the UI thread. If you need to update UI widgets from UDPReadThread, that's the code that needs the asyncExec:
display.asyncExec(
new Runnable() {
public void run(){
label.setText(text);
}
});
Just as an aside, you should not subclass Thread unless you really are extending threads capabilities. The normal pattern when you just want to start another thread:
UDPReadRunnable udpRunnable = ....;
Thread thread = new Thread(udpRunnable);
thread.start();
You can get more information on the display thread from http://www.eclipse.org/swt/faq.php#uithread
I have a program which runs a thread. The thread performs processing all the time and it uses some synchronized queue.
The class snapshot is as follows:
public class MyClass:IDisposable
{
private Thread myThread = new Thread(threadFunc);
private volatile bool runThread = true;
public MyClass()
{
myThread.Start();
}
public Dispose()
{
runThread = false;
}
private void threadFunc()
{
try
{
while(runThread){
queue.Take(); //This method blocks the thread if queue is empty. It uses Monitor class
//do some processing
}
}
catch(Exception e){...}
}
private void otherFunc()
{
queue.enqueue(...);//this method is executed by main thread and uses lock while adding element to the queue.
}
}
When I call Dispose() method, the thread exists threadFunc() method, but after a sec I get an execption from this func "Unable to avaluate expression...", as if the tread was terminated while doing some work. Maybe it has just released from queue.Take() blocking and has no context to run. I know I'm missing something...
How can I solve such problem and terminate the thread from the Dispose method.
Many thanks!!!
Use the overload of Take that accepts a CancellationToken. You can get a reference to a token by using the CancellationTokenSource which also has the Cancel method that you can call from Dispose to unblock the Take method. You can read more cancellation here.
Use the poison pill approach: See this thread