javafx - 对话框关闭时取消任务

Question

在 javafx 应用程序中，我有一个方法 retrain(String)，由于简单的实现(教育)，该方法在大量输入上需要很长时间。我在加载时打开一个对话框，我希望用户能够取消/关闭该对话框并且任务将退出。有没有办法在不传递对任务的引用进行重新训练的情况下执行此操作。现在我认为当我取消线程时，线程被取消，但重新训练仍在后台运行。

任何提示将不胜感激!

@FXML
        private void handleMarkovText() {
            textgen.MarkovTextGenerator mtg = mainApp.getMTG();
            Task<textgen.MarkovTextGenerator> task = new Task<textgen.MarkovTextGenerator>() {
                @Override
                public textgen.MarkovTextGenerator call() {
                    // process long-running computation, data retrieval, etc...

                mtg.retrain(textBox.getText());
                return mtg;
            }
        };

        Dialog<Void> loadDialog = new Dialog<Void>();
        loadDialog.setOnCloseRequest( e -> {
            //if(task.isRunning()) {
                task.cancel();

            //}
        });

        loadDialog.setContentText("Training MTG...");

        task.setOnRunning( e -> {
            ButtonType cancelButtonType = new ButtonType("Cancel", ButtonData.CANCEL_CLOSE);
            //Dialog<Void> loadDialog = new Dialog<Void>();
            loadDialog.getDialogPane().getButtonTypes().add(cancelButtonType);
            loadDialog.show();
            if(task.isCancelled()) {
            }
        });


        task.setOnSucceeded(e -> {
            loadDialog.close();
            textgen.MarkovTextGenerator result = task.getValue();
            mainApp.showMarkovDialog(result);
            // update UI with result
        });

        task.setOnCancelled(e -> {
            System.out.println("Cancelled");
        });

        task.setOnFailed(e -> {
            //System.out.println("failed");
        });
        //ProgressBar bar = new ProgressBar();
        //bar.progressProperty().bind(task.progressProperty());
       Thread thread  = new Thread(task);
       thread.start();





        // train/retrain markov
        // show results

    }

Answer 1

在重新训练方法中处理任务取消

您的retrain方法需要了解任务取消状态。它可以通过轮询 task.isCancelled 来做到这一点在适当的时候。如果检测到取消，重写方法可以自行清理(释放它正在消耗的任何资源并确保取消状态在语义上与您的应用程序一致)并且不进行任何进一步的处理(有效地允许执行重写的线程退出) 。

示例代码

Task 中提供了取消检查的示例代码。标题为“带有进度通知和阻止调用的简单循环”的文档。

背景信息

来自任务 javadoc 的相关信息:

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 FutureTask, to see whether the Task has been cancelled. Second, if the Task implementation makes use of any blocking calls (such as NIO InterruptibleChannels or Thread.sleep) and the task is cancelled while in such a blocking call, an InterruptedException is thrown. 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.

使用线程的中断状态

如果您不想让您的 retrain 方法引用任务 API(因为您想将其与 JavaFX 任务 API 解耦或出于其他原因)，您也许可以实现与通过调用 Thread.currentThread().isInterrupted() 进行的 task.isCancelled 检查类似的行为从您的retrain方法中的适当位置。

下面列出的 Goetz 文章中的 list 5:PrimeProducer 举例说明了这种方法。

JavaFX任务，实现futureTask，这样你就可以调用cancel(boolean mayInterruptIfRunning)将 mayInterruptIfRunning 设置为 true，并且应该在执行任务的线程上设置中断状态(在您的情况下，它将执行 rewrite 方法)。

有关处理取消线程工作的一般过程的背景信息:Java theory and practice: Dealing with InterruptedException (布莱恩·戈茨的文章。

注意:无论您使用任务取消还是线程中断状态检查，无论哪种情况，您都需要自定义 rewrite 方法，您需要修改该方法以使其能够处理适当取消或中断。