What is the correct way to schedule a task to be executed, but not block calling thread.
Is this the correct way of doing so?
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class Main {
public static void main(String [] args) throws ExecutionException, InterruptedException {
final ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
ScheduledFuture<?> f = service.schedule(new Runnable() {
public void run() {
System.out.println("Before sleep");
try {
Thread.sleep(50000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("After sleep");
}
}, 0, TimeUnit.MINUTES);
try {
f.get(0, TimeUnit.MINUTES);
} catch (TimeoutException e) {
//
}
System.out.println("Main thread");
}
}
As far as I understand if I just call f.get(), then it will block calling thread till the completion of future. What I am trying to do is to submit the tasks, but do not block caller threads.
Calling f.get() will block only if the task hasn't finished yet. If the task is finished, it will just return its result without blocking.
If you don't care about the result and just want to run some tasks, simply ignore the Future returned by schedule().
Related
I'm trying to update text inside a javafx textArea element instantly to show execution information using both thread and task but nothing seems working, althought when I print something in console it works thus the thread is executing. The program prints all the messages once the program is executed, but i want show the messages as the same time as the program is executing.
Here I have my tsak and thread declarations
#Override
public void initialize(URL url, ResourceBundle rb) {
System.setProperty("webdriver.gecko.driver", "C:\\Users/lyesm/Downloads/geckodriver-v0.26.0-win64/geckodriver.exe");
try {
restoreValues();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
text = new Text(this.getLogs());
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
Runnable updater = new Runnable() {
#Override
public void run() {
printMessages();
System.out.println(" working on ... \n");
}
};
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
}
//Platform.runLater(updater);
}
}
});
thread.setDaemon(true);
thread.start();
service = new Service<Void>() {
#Override
protected Task<Void> createTask() {
return new Task<Void>() {
#Override
protected Void call() throws Exception {
Platform.runLater(() -> textArea.appendText(logs));
return null;
}
};
}
};
service.start();
}
I'm calling the service from this method
public void launchTest() {
this.setLogs("\n\n");
service.restart();
this.setLogs(" Test starting ...\n");
service.restart();
//this.setLogs(" Opening the navigator \n");
this.setDriver(new FirefoxDriver());
//this.setLogs(" Reaching http://127.0.0.1:8080/booksManager ... \n");
driver.get("http://127.0.0.1:8080/booksManager");
//this.setLogs(" Setting test data \n");
driver.findElement(By.id("lyes")).click();
driver.findElement(By.name("email")).sendKeys(pseudo.getText());
driver.findElement(By.name("password")).sendKeys(password.getText());
//this.setLogs(" Submitting ... \n");
driver.findElement(By.name("submit")).click();
if(driver.getCurrentUrl().equals("http://127.0.0.1:8080/booksManager/Views/index.jsp") == true) {
//InputStream input= getClass().getResourceAsStream("https://w0.pngwave.com/png/528/278/check-mark-computer-icons-check-tick-s-free-icon-png-clip-art-thumbnail.png");
//Image image = new Image(input);
//ImageView imageView = new ImageView(image);
Label label = new Label(" Test successed");
testsInfos.getChildren().add(label);
}else {
Text textRes = new Text("\n Test failed ");
textRes.setFill(javafx.scene.paint.Color.RED);
testsInfos.getChildren().add(textRes);
}
driver.close();
}
And here the printMessage method called from the thread
public void printMessages() {
String ll = this.getLogs();
this.text.setText(ll);
testsInfos.getChildren().remove(text);
testsInfos.getChildren().add(text);
textArea.clear();
textArea.setText(ll);
}
Neither method seems to work.
Does anybody have any idea how to fix it ?
Edited:
package application;
import java.util.concurrent.CountDownLatch;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.layout.StackPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;
public class Main extends Application {
private Service<Void> service;
#Override
public void start(Stage primaryStage) throws InterruptedException {
StackPane root = new StackPane();
TextArea ta = new TextArea();
ta.setDisable(true);
root.getChildren().add(ta);
Scene scene = new Scene(root, 200, 200);
// longrunning operation runs on different thread
/*Thread thread = new Thread(new Runnable() {
#Override
public void run() {
Runnable updater = new Runnable() {
#Override
public void run() {
incrementCount();
}
};
while (true) {
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
}
// UI update is run on the Application thread
Platform.runLater(updater);
}
}
});
// don't let thread prevent JVM shutdown
thread.setDaemon(true);
thread.start();*/
primaryStage.setScene(scene);
primaryStage.show();
service = new Service<Void>() {
#Override
protected Task<Void> createTask() {
return new Task<Void>() {
#Override
protected Void call() throws Exception {
final CountDownLatch latch = new CountDownLatch(1);
Platform.runLater(new Runnable() {
#Override
public void run() {
try{
ta.appendText("\n Printed ");
}finally{
latch.countDown();
}
}
});
latch.await();
return null;
}
};
}
};
service.start();
showIT();
}
public static void main(String[] args) {
launch(args);
}
public void showIT() throws InterruptedException {
service.restart();
for(int i = 0;i<1000000;i++) {
System.out.println(i);
}
for(int i = 0;i<1000000;i++) {
System.out.println(i);
}
service.restart();
for(int i = 0;i<1000000;i++) {
System.out.println(i);
}
for(int i = 0;i<1000000;i++) {
System.out.println(i);
}
service.restart();
}
}
The two threading rules in JavaFX are:
Long-running code must not be executed on the FX Application Thread, and
Any code that updates the UI must be executed on the FX Application Thread.
The reason for the first rule is that the FX Application Thread is responsible for rendering the UI (among other things). So if you perform a long-running task on that thread, you prevent the UI from being rendered until your task is complete. This is why you only see the updates once everything is finished: you are running your long-running code on the FX Application Thread, preventing it from re-rendering the text area until everything is complete.
Conversely, the code you do run on a background thread (via the Task.call() method) doesn't do anything that takes a long time to run:
#Override
protected Void call() throws Exception {
final CountDownLatch latch = new CountDownLatch(1);
Platform.runLater(new Runnable() {
#Override
public void run() {
try{
ta.appendText("\n Printed ");
}finally{
latch.countDown();
}
}
});
latch.await();
return null;
}
The only thing you do here is schedule an update on the FX Application thread; the call to Platform.runLater() exits immediately. There's no long-running code at all, so no purpose for the background thread on which this runs. (Technically, the call to latch.await() is a blocking call, but it's redundant anyway, since you simply exit the method after waiting.) With this task implementation, there's no difference between calling service.restart();, and ta.appendText("\n Printed");.
So, your showIT() method should be called on a background thread, and can use Platform.runLater() to append text to the text area. Something like:
import java.util.concurrent.CountDownLatch;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.layout.StackPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;
public class Main extends Application {
private Service<Void> service;
#Override
public void start(Stage primaryStage) throws InterruptedException {
StackPane root = new StackPane();
TextArea ta = new TextArea();
ta.setDisable(true);
root.getChildren().add(ta);
Scene scene = new Scene(root, 200, 200);
primaryStage.setScene(scene);
primaryStage.show();
// run showIT() on a background thread:
Thread thread = new Thread(this::showIT);
thread.setDaemon(true);
thread.start();
}
public static void main(String[] args) {
launch(args);
}
public void showIT() {
try {
Platform.runLater(() -> ta.appendText("\nPrinted"));
Thread.sleep(1000);
Platform.runLater(() -> ta.appendText("\nPrinted"));
Thread.sleep(1000);
Platform.runLater(() -> ta.appendText("\nPrinted"));
Thread.sleep(1000);
} catch (InterruptedException exc) {
Thread.currentThread().interrupt();
}
}
}
For your original code, I have to make some guesses about which parts of the API you're using are long-running and which aren't. I would start by creating a utility log() method that you can call from any thread:
private void log(String message) {
Runnable update = () -> ta.appendText(message);
// if we're already on the FX application thread, just run the update:
if (Platform.isFxApplicationThread()) {
update.run();
}
// otherwise schedule it on the FX Application Thread:
else {
Platform.runLater(update);
}
}
And now you can do something like:
public void launchTest() {
log("\n\n");
log(" Test starting ...\n");
log(" Opening the navigator \n");
Task<Boolean> task = new Task<>() {
#Override
protected Boolean call() throws Exception {
this.setDriver(new FirefoxDriver());
log(" Reaching http://127.0.0.1:8080/booksManager ... \n");
driver.findElement(By.name("email")).sendKeys(pseudo.getText());
driver.findElement(By.name("password")).sendKeys(password.getText());
driver.get("http://127.0.0.1:8080/booksManager");
log(" Setting test data \n");
driver.findElement(By.id("lyes")).click();
log(" Submitting ... \n");
driver.findElement(By.name("submit")).click();
boolean result = driver.getCurrentUrl().equals("http://127.0.0.1:8080/booksManager/Views/index.jsp");
driver.close();
return result ;
}
};
task.setOnSucceeded(e -> {
if (task.getValue()) {
//InputStream input= getClass().getResourceAsStream("https://w0.pngwave.com/png/528/278/check-mark-computer-icons-check-tick-s-free-icon-png-clip-art-thumbnail.png");
//Image image = new Image(input);
//ImageView imageView = new ImageView(image);
Label label = new Label(" Test successed");
testsInfos.getChildren().add(label);
} else {
Text textRes = new Text("\n Test failed ");
textRes.setFill(javafx.scene.paint.Color.RED);
testsInfos.getChildren().add(textRes);
}
});
Thread thread = new Thread(task);
thread.setDaemon(true);
thread.start();
}
I encountered a strange problem while using ExecutorService to execute a Callable in static block. let's see the complete code directly as below.
package com.acme;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class App {
private static int data = 0;
static {
ExecutorService executor = Executors.newFixedThreadPool(1);
Future<String> future = executor.submit(new Callable<String>() {
#Override
public String call() throws Exception {
System.out.println("" + data);
return "hello";
}
});
}
public static void main(String[] args) {
System.out.println("enter main scope");
}
}
Run the main method, the result is presented as below screenshot.
enter image description here
However, if I add some business code as below, nothing is printed in the console.
public class App {
private static int data = 0;
static {
ExecutorService executor = Executors.newFixedThreadPool(1);
Future<String> future = executor.submit(new Callable<String>() {
#Override
public String call() throws Exception {
System.out.println("" + data);
return "hello";
}
});
try {
future.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
System.out.println("enter main scope");
}
}
Anyone can provide some help about this issue? more details are preciated.
As you made executor code run in static block which force the code to run even before App.class context is full created (i.e class not fully loaded in memory or you can say now "data" variable is not in memory ).
Basically when your call method get called through executor its(thread) trying to find the variable "data" in App.class but it might not be loaded till now, this is also making thread run infinite.
Solution :
Run the executor in main block but still there is a issue ,suppose if for some reason (business logic) the App.class get unloaded you will be again stuck with a infinitely running thread that is finding "data".
Make the data variable "final", then you can put your code either is static block or static method (Ex. main). As for final variable a separate copy is maintained and has issue of class loading or unloading above issue will not come.
I am trying to run a thread in background with while(true) condition, and not using any join after the thread so that it continue running the main thread. But what I am observing is only while loop is running and it is not switching to main thread. please help me find the issue. This is Groovy code.
public static void main(args) {
Thread.start {
while (true) {
long sleepMillis = 2000
System.out.println("inside async block")
Thread.sleep(sleepMillis)
}
}
//main func code goes here
}
Please give me pointers to the issue.
Here You go:
public class Lol {
public static void main(String[] args) {
def t = new Thread(new Runnable() {
public void run() {
while(true) {
println 'lol'
Thread.sleep(500)
}
}
}).start()
println 'other'
}
}
I am trying to implement a program where I want different Components to blink at different speeds. I am using threads. But its not working.
How can I implement this.
This is the void run function in the class that implements runnable
public void run()
{
try
{
while(true)
{
Thread.sleep(1000);
if(isVisible()==true)
{
setVisible(false);
}
else
{
setVisible(true);
}
repaint();
}
}
catch(InterruptedException e)
{
}
}
}
and this is the class (its in a paint component of the main JPanel)where I call the threads-
{
cars[i]=new Car(color, xLocation, yLocation, speed, type, i, widthController, heightController);
cars[i].setBounds(widthController+(xLocation*50)+10, heightController+(yLocation*50)+10, 30, 30);
add(cars[i]);
threads[i]=new Thread(cars[i]);
threads[i].start();
}
cars is an array of JComponents of which void run is part of.
Thanks
With Swing, all operations that affect visible components should be run on the AWT-EventQueue. This is a dedicated thread for Input/Output operations as well as drawing and component operations. My recommendation is to use a swing timer for your run operation. The repaint call you made will call the paintCompnent method on the AWT-EventQueue. However you're changing the state of visibility on a seperate thread. This means that by the time the repaint call is made, it's possible the state has already changed to the previous value.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JPanel;
import javax.swing.Timer;
//Rest of code above...
//This will execute the timer every 500 milliseconds
Timer aTimer = new Timer(500, new ActionListener() {
#Override
public void actionPerformed(ActionEvent pE) {
aComponent.setVisible(!aComponent.isVisible());
}
});
aTimer.start();
Another option is that on each thread add this call:
//This should be added inside of your thread
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
aComponent.setVisible(!aComponent.isVisible());
}
});
Here's the answer I was alluding to in my comments:
public void run()
{
try
{
while(true)
{
Thread.sleep(1000);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
setVisible(!isVisible());
}
}
});
}
catch(InterruptedException e)
{
}
I have a TableView associated with some data, and once i hit a run button i perform some processing on that data. Each row of data is handled in a seperate thread, and while those threads are running i want a ProgressInducator to replace the table within its vbox.
In the attached code:
If I stop where is says "WORKS IF STOP HERE" - table is replaced with pi.
If I continue waiting for the threads to join - no replacing.
What am I missing?
runButton.setOnAction(
new EventHandler<ActionEvent>() {
#Override
public void handle(final ActionEvent e) {
List<Thread> threadList = new ArrayList<Thread>();
int threadCounter = 0;
final ProgressIndicator pi = new ProgressIndicator(threadCounter);
vbox.getChildren().clear();
vbox.getChildren().addAll(pi);
for (ProductInTable product : data) {
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
try
{
product.calculate();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
});
threadList.add(thread);
thread.start();
}
int x = threadList.size();
/** WORKS IF STOP HERE **/
// wait for all threads to end
for (Thread t : threadList) {
try {
t.join();
threadCounter++;
pi.setProgress(threadCounter / x);
} catch (InterruptedException interE) {
interE.printStackTrace();
}
}
/** DOESNT WORKS IF STOP HERE **/
Thread.join() blocks execution until the thread is completed. Since you are calling this on the FX Application Thread, you block that thread until all your worker threads finish. This means the UI is unable to update until those threads are complete.
A better approach is probably to represent each computation with a task, and update a counter of complete tasks back on the FX Application Thread using setOnSucceeded. Something like:
runButton.setOnAction(
new EventHandler<ActionEvent>() {
#Override
public void handle(final ActionEvent e) {
final ProgressIndicator pi = new ProgressIndicator(threadCounter);
vbox.getChildren().clear();
vbox.getChildren().addAll(pi);
final int numTasks = data.size();
// only access from FX Application thread:
final IntegerProperty completedTaskCount = new SimpleIntegerProperty(0);
pi.progressProperty().bind(completedTaskCount.divide(1.0*numTasks));
completedTaskCount.addListener(new ChangeListener<Number>() {
#Override
public void changed(ObservableValue<? extends Number> obs, Number oldValue, Number newValue) {
if (newValue.intValue() >= numTasks) {
// hide progress indicator and show table..
}
}
});
for (final ProductInTable product : data) {
Task<Void> task = new Task<Void>() {
#Override
public Void call() {
try
{
product.calculate();
} catch (IOException ioe) {
ioe.printStackTrace();
}
return null ;
}
});
task.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent event) {
completedTaskCount.set(completedTaskCount.get()+1);
}
});
new Thread(task).start();
}
}
});
If you potentially have a large number of items here, you should use some kind of ExecutorService instead to avoid creating too many threads:
ExecutorService exec = Executors.newFixedThreadPool(
Runtime.getRuntime().availableProcessors()); // for example...
and then replace
new Thread(task).start();
with
exec.submit(task);