Javafx thread

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Javafx thread

December 4, 2 min read. One of my MouseEvents made use of a Thread in order to continue moving images even when the images were no longer being clicked on.

Despite making sure that I would never concurrently ask the scene to do multiple things at once, I was still randomly receiving ConcurrentModificationExceptions as below:. The stack trace is not terribly helpful as the exception does not occur in my code, but after some research, it was quite clear that the issue is that the scene is NOT thread safe.

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So, if you are modifying the Scene Graph from within a Thread, you need to use Platform. It is also worth a reminder that if you are using a boolean declared and used outside a thread that also gets used in a thread, make sure to use the volatile keyword to disable any unwanted caching or other optimisations.

I have written several articles on converting our Java3D usage into JavaFX and you can read the other articles here. On the blog our team post about anything interesting they learn about.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Notify me of follow-up comments by email. Notify me of new posts by email. Reply 0. He oversees the BuildVu product strategy and roadmap in addition to spending lots of time writing code. Mark Stephens Jan 26, 58 sec read. Leave a Reply Cancel reply Your email address will not be published.This chapter describes the capabilities provided by the javafx. You learn how to keep your JavaFX application user interface UI responsive by delegating time-consuming task execution to background threads.

A best practice is to do these tasks on one or more background threads and let the JavaFX Application thread process user events. If you have special requirements or need extra power over the code, implementing a background worker by creating a Runnable object and a new thread is an appropriate way to go. Note that at some point you must communicate with the JavaFX Application thread, either with a result or with the progress of the background task.

For the most cases and for the majority of developers the recommended way is to use the JavaFX APIs provided by the javafx.

Handling Threads & Concurrency in JavaFX

The Java platform provides a complete set of concurrency libraries available through the java. The javafx. The Task class is a fully observable implementation of the java. FutureTask class.

The Task class enables developers to implement asynchronous tasks in JavaFX applications. The Service class executes tasks. The WorkerStateEvent class specifies an event that occurs whenever the state of a Worker implementation changes. Both the Task and Service classes implement the EventTarget interface and thus support listening to the state events. The Worker interface defines an object that performs some work on one or more background threads.

The lifecycle of the Worker object is defined as follows. Otherwise, if any exceptions are thrown during the execution of the Worker object, its state becomes FAILED and the exception property is set to the type of the exception that occurred.

The progress of the work being done by the Worker object can be obtained through three different properties such as totalWorkworkDoneand progress. Tasks are used to implement the logic of work that needs to be done on a background thread. First, you need to extend the Task class. Your implementation of the Task class must override the call method to do the background work and return the result. The call method is invoked on the background thread, therefore this method can only manipulate states that are safe to read and write from a background thread.

For example, manipulating an active scene graph from the call method throws runtime exceptions. On the other hand, the Task class is designed to be used with JavaFX GUI applications, and it ensures that any changes to public properties, change notifications for errors or cancellation, event handlers, and states occur on the JavaFX Application thread.

Inside the call method, you can use the updateProgressupdateMessageupdateTitle methods, which update the values of the corresponding properties on the JavaFX Application thread. However, if the task was canceled, a return value from the call method is ignored. Note that the Task class fits into the Java concurrency libraries because it inherits from the java.

FutureTask class, which implements the Runnable interface. For this reason, a Task object can be used within the Java concurrency Executor API and also can be passed to a thread as a parameter. You can call the Task object directly by using the FutureTask. The Task class defines a one-time object that cannot be reused. If you need a reusable Worker object, use the Service class. There is no reliable way in Java to stop a thread in process. However, the task must stop processing whenever cancel is called on the task.

The task is supposed to check periodically during its work whether it was cancelled by using the isCancelled method within the body of the call method. Example shows a correct implementation of the Task class that checks for cancellation. If the task implementation has blocking calls such as Thread. For these tasks, an interrupted thread may be the signal for a cancelled task.I have an FXML file that lays out some components onto a panel.

Since there are multiple instances of the panel that are composited together think of it as a VBox with several chartsI've been experimenting with ways of initializing the panels in their own threads. The gist of the task is that it should:. My initial assumption was that I could stick all of this into the Task call method but I immediately got an exception because the FXML Loader wasn't on the application thread. Is there some reason that loading a component's configuration needs to be on the application thread?

Ideally, it should only care when I attempt to add that component to the scene graph. It uses the call method to construct a model for the chart, and then uses the succeeded method to bind the model to the chart. Since both scheduled and succeeded are supposed to be on the app thread, this should work.

My assumption was that behind the scenes, Task was executing the methods in the following order: scheduled, call, succeeded or failed as the case may be.

However, when I try to get the panel returned by the call method, I always get null. Since I'm calling the task using the ThreadPoolExecutor, and getting a Future, I expect that the Future should always give me the results of the call method, and that this would be non-null since the panel is initialized in the scheduled method. Which version of JavaFX are you using? This simplified test works in JavaFX 2. It seems to me this should work, as nothing is being done in the background thread that changes anything in the live scene graph.

You would think you could do anything set field values, set attributes for components off of the application thread. Adding a visible object to the scene graph should cause the object to go through the layout process and this would necessarily involve calculating bounds, and other activities that would require access to the app thread. The reason it causes a problem is that things like a ContextMenu or Tooltip are implemented as PopupControls with their own windows and in JavaFX, currently windows must be created on the JavaFX application thread.

Randahl found a clever hack mentioned in comments on the jira below of defining your own skin which delays the creation of the Popup, but I'm not sure I'd like to do that. There's no obvious reason my sample should fail in JavaFX 8, is there? Can you can reproduce that?

If so I'll file it; the reason I ask is that the behavior is very odd. If I remove the Thread. If I run it once omit the loopwith the Thread.

If I include the loop, and the Thread. Label errors The reason for the failure of your code with Java 8 is some static initialization code which was added to Control. As Control a fundamental class, if it does not load, then you can't create anything that subclasses it i.

javafx thread

As classloading is related to the class loader, which is not thread specific, it doesn't matter if subsequent control creation attempts are on or off the JavaFX application thread - any subsequent control constructor usage will fail.

You don't have to do anything with the Label or put it on the Scene, the call is just there to get the Control class loaded into the VM with the static initializer run on the JavaFX application thread.

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Caused by: java.A fully observable implementation of a FutureTask. Tasks exposes additional state and observable properties useful for programming asynchronous tasks in JavaFX, as defined in the Worker interface. An implementation of Task must override the call method. This method is invoked on the background thread. Any state which is used in this method must be safe to read and write from a background thread.

For example, manipulating a live scene graph from this method is unsafe and will result in runtime exceptions. Tasks are flexible and extremely useful for the encapsulation of "work". Because Service is designed to execute a Task, any Tasks defined by the application or library code can easily be used with a Service.

Since a Task is Runnable, you can also call it directly by invoking the FutureTask. This allows for composition of work, or pass it to a new Thread constructed and executed manually.

If you want a background thread to prevent the VM from existing after the last stage is closed, then you would want daemon to be false. However, if you want the background threads to simply terminate after all the stages are closed, then you must set daemon to true. Although ExecutorService defines several methods which take a Runnable, you should generally limit yourself to using the execute method inherited from Executor.

As with FutureTask, a Task is a one-shot class and cannot be reused. See Service for a reusable Worker. Because the Task is designed for use with JavaFX GUI applications, it ensures that every change to its public properties, as well as change notifications for state, errors, and for event handlers, all occur on the main JavaFX application thread. Accessing these properties from a background thread including the call method will result in runtime exceptions being raised.

The only exception to this, is when initially configuring a Task, which may safely be done from any thread. However, once the Task has been initialized and started, it may only thereafter be used from the FX thread except for those methods clearly marked as being appropriate for the subclass to invoke from the background thread.

It is strongly encouraged that all Tasks be initialized with immutable state upon which the Task will operate. This should be done by providing a Task constructor which takes the parameters necessary for execution of the Task. Immutable state makes it easy and safe to use from any thread and ensures correctness in the presence of multiple threads.

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In Java there is no reliable way to "kill" a thread in process. However, when cancel is called on a Task, it is important that the Task stop processing. A "run-away" Task might continue processing and updating the message, text, and progress properties even after the Task has been cancelled! In Java, cancelling a Task is a cooperative endeavor. The user of the Task will request that it be cancelled, and the author of the Task must check whether is has been cancelled within the body of the call method.

There are two ways this can be done. First, the Task author may check the isCancelled method, inherited from FutureTaskto see whether the Task has been cancelled. Task implementations which have blocking calls should recognize that an interrupted thread may be the signal for a cancelled task and should double check the isCancelled method to ensure that the InterruptedException was thrown due to the cancellation of the Task. The first example is a simple loop that does nothing particularly useful, but demonstrates the fundamental aspects of writing a Task correctly.

This example will simply loop and print to standard out on each loop iteration. When it completes, it returns the number of times it iterated. First, we define what type of value is returned from this Task. In this case, we want to return the number of times we iterated, so we will specify the Task to be of type Integer by using generics.

Then, within the implementation of the call method, we iterate from 0 to On each iteration, we check to see whether this Task has been cancelled.

If it has been, then we break out of the loop and return the number of times we iterated. Otherwise a message is printed to the console and the iteration count increased and we continue looping. Checking for isCancelled in the loop body is critical, otherwise the developer may cancel the task, but the task will continue running and updating both the progress and returning the incorrect result from the end of the call method.Irina has written tutorials and technical articles on Java and JavaFX technologies.

She lives in St. Petersburg, Russia. In her spare time, she enjoys swing dancing, playing piano, and reading.

Release: JavaFX 2.1

Send us feedback about this document. If you have questions about JavaFX, please go to the forum. This article describes the capabilities provided by the javafx. You learn how to keep your JavaFX application user interface UI responsive by delegating time-consuming task execution to background threads. A best practice is to do these tasks on one or more background threads and let the JavaFX Application thread process user events.

If you implement a background worker by creating a Runnable object and a new thread, at some point, you must communicate with the JavaFX Application thread, either with a result or with the progress of the background task, which is error prone.

The Java platform provides a complete set of concurrency libraries available through the java. The javafx. The Task class is a fully observable implementation of the java. FutureTask class. The Task class enables developers to implement asynchronous tasks in JavaFX applications. The Service class executes tasks. The WorkerStateEvent class specifies an event that occurs whenever the state of a Worker implementation changes. Both the Task and Service classes implement the EventTarget interface and thus support listening to the state events.

The Worker interface defines an object that performs some work on one or more background threads. The lifecycle of the Worker object is defined as follows. Otherwise, if any exceptions are thrown during the execution of the Worker object, its state becomes FAILED and the exception property is set to the type of the exception that occurred. The progress of the work being done by the Worker object can be obtained through three different properties such as totalWorkworkDoneand progress.

Tasks are used to implement the logic of work that needs to be done on a background thread. First, you need to extend the Task class. Your implementation of the Task class must override the call method to do the background work and return the result.

JavaFX Software: Weather App (MVC, Multithreading)

The call method is invoked on the background thread, therefore this method can only manipulate states that are safe to read and write from a background thread. For example, manipulating an active scene graph from the call method throws runtime exceptions. On the other hand, the Task class is designed to be used with JavaFX GUI applications, and it ensures that any changes to public properties, change notifications for errors or cancellation, event handlers, and states occur on the JavaFX Application thread.

Inside the call method, you can use the updateProgressupdateMessageupdateTitle methods, which update the values of the corresponding properties on the JavaFX Application thread. However, if the task was canceled, a return value from the call method is ignored. Note that the Task class fits into the Java concurrency libraries because it inherits from the java. FutureTask class, which implements the Runnable interface.

For this reason, a Task object can be used within the Java concurrency Executor API and also can be passed to a thread as a parameter.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am developing my first application, and I use javafx for my GUI part. In this code, while pressing the button, I am trying to connect to mail server:.

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Exception in thread "Thread-4" java. But I am not sure know how to this make in my app.

Release: JavaFX 2.1

This my controller from which I open new window:. You may also want look at this question. There is another way to make a thread to an FX User Thread, but this seems to be a bug within JavaFX and thus may be patched out in the future.

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You'll need to use the following:. For further reading, take a look at Platform. How are we doing? Please help us improve Stack Overflow. Take our short survey. Learn more.

javafx thread

How can I create Thread in javafx [duplicate] Ask Question. Asked 4 years, 9 months ago. Active 4 years, 9 months ago. Viewed 6k times. Thanks, experts. Turing85 9, 4 4 gold badges 23 23 silver badges 43 43 bronze badges. Anton Konikov Anton Konikov 49 1 1 silver badge 7 7 bronze badges. Active Oldest Votes.Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon.

When code running in some thread creates a new Thread object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.

javafx thread

When a Java Virtual Machine starts up, there is usually a single non-daemon thread which typically calls the method named main of some designated class. 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. There are two ways to create a new thread of execution.

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One is to declare a class to be a subclass of Thread. This subclass should override the run method of class Thread. An instance of the subclass can then be allocated and started.

That class then implements the run method. An instance of the class can then be allocated, passed as an argument when creating Threadand started. More than one thread may have the same name. If a name is not specified when a thread is created, a new name is generated for it. Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown. Since: JDK1. State A thread state. UncaughtExceptionHandler Interface for handlers invoked when a Thread abruptly terminates due to an uncaught exception.

The definition of this call depends on suspendwhich is deprecated. Further, the results of this call were never well-defined. This method was originally designed to destroy this thread without any cleanup.

Any monitors it held would have remained locked. However, the method was never implemented. If if were to be implemented, it would be deadlock-prone in much the manner of suspend. If the target thread held a lock protecting a critical system resource when it was destroyed, no thread could ever access this resource again.

javafx thread

If another thread ever attempted to lock this resource, deadlock would result. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread. UncaughtExceptionHandler getDefaultUncaughtExceptionHandler Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception. String getName Returns this thread's name.


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