Is there a when process ends method in java?

I am trying to search when GTA5.exe ends. It launches with "steam://rungameid" protocol, so I can't use Process#waitFor(); method.

The method below checks if (currently) the process is running

public static boolean isProcessRunning(String processName) throws IOException {
        ProcessBuilder processBuilder = new ProcessBuilder("tasklist.exe");
        Process process = processBuilder.start();
        String tasksList = toString(process.getInputStream());

        return tasksList.contains(processName);
}

But what I want is something like

waitUntilProcessEnds(String processname) {
}

It could be

while (isProcessRunning) {
Thread.sleep(1000);
}

And, as expected, my JavaFX app freezes.
If I try to run the while method in another Thread, my JavaFX App gives this error:

java.lang.IllegalStateException: Not on FX application thread; currentThread = Thread-6
	at com.sun.javafx.tk.Toolkit.checkFxUserThread(Toolkit.java:279)
	at com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(QuantumToolkit.java:444)
	at javafx.scene.control.Dialog.show(Dialog.java:294)
	at com.thunderstorm.gta5.mod_installer.app.AppController$1$1.run(AppController.java:101)
	at java.lang.Thread.run(Thread.java:748)

I also tried this

Platform.runLater();

and this

Platform.setImplicitExit(false);

But nothing different...

How to fix this

This question is edited

There is an API, but it requires Java 9 or newer. Then, you can do it smoothly:

String name = "GTA5.exe";
ProcessHandle.allProcesses()
    .filter(ph -> ph.info().command()
        .filter(s -> s.regionMatches(true,s.length()-name.length(),name,0,name.length()))
        .isPresent())
    .findAny()
    .ifPresentOrElse(ph -> {
        System.out.println("Waiting for "+ph.pid()+" "+ph.info().command().get());
        ph.onExit().thenRunAsync(() -> {
            // your actual action
        }, Platform::runLater);
    }, () -> System.out.println("No matching process found"));

ProcessHandle.onExit() returns a CompletableFuture which allows to chain dependent actions, to be performed on the process’ completion. So you don’t need to poll the process yourself.

Further note that Platform.runLater(Runnable) matches the functional signature of the Executor interface which allows us to use thenRunAsync(…, Platform::runLater) to mandate that the dependent action (Runnable) should be executed in the JavaFX Application Thread, once the process has exited.

I think your design is ok, but you're a bit confused by the threads. First when you start your wait method, go ahead and start a new Thread.

new Thread( ()->{
     waitUntilProcessEnds(processname);
     Platform.runLater( ()-> callBackOnPlatformThread() );
}).start();

Then you need.

public void callBackOnPlatformThread(){
    System.out.println("go ahead and modify fx components.");
}

This will start waiting for the process to end on a new thread, so your javafx UI will continue to be responsive. When it is finished, it calls back on the javafx Platform thread, so you can modify components.

This doesn't check if the thread has already been started, so if you have a button that starts the thread, you could start a bunch of them.

What are you trying to achieve? If you want to execute some code when your application ends then you can add a shutdown hook:

Runtime.getRuntime().addShutdownHook(() -> { ... });

If you want to wait until the external process ends, then you can use:

process.waitFor()

This will block your current thread until the external process exits.

Not if your program didn't create the process in the first place.

Java does not provide operating-system level facilities that are not provided in the underlying OS in the first place. In Unix-like systems, for example, "wait for process exit" can only be executed by an ancestor of the process in question. In Windows, for another example, you have to possess a handle on the process, which you would have obtained from creating the process.

You'll have to roll your own. Create a thread which periodically checks for the existence of the process you are monitoring, by whatever means is suitable to that process and your operating environment. Worst-case you'll have to fork a 'ps' command (or similar) and parse the output.

I can't advise on the JavaFX issue; not my area.