I'm trying get more experience with the new Foreign Function & Memory API in Java 22+. The best way how to learn a new API is by using it in a project.
My project’s goal is to report on the taskbar the progress of some long-running task. As far as I know, there is no "native" support of this in JavaFX. There are some libraries like FXTaskbarProgressBar which serves the purpose, but only for Windows OS. And it is using the "old" Java Native Interface (JNI).
After a short research, I found a simple Go library taskbar. This library inspired me to try porting to Java for JavaFX.
First I used jextract to get java bindings to native library calls:
jextract --output target/generated-sources/jextract -t "taskbar_test.gen" --include-function "XOpenDisplay" --include-function "XChangeProperty" --include-function "XFlush" --include-function "XCloseDisplay" /usr/include/X11/Xlib.h
Then I created a simple application to simulate long running process where I try to update progress on taskbar by calling method "XChangeProperty" which I found in documentation of X11: https://www.x.org/releases/X11R7.7/doc/libX11/libX11/libX11.html#XChangeProperty
Unfortunately this does not work. The program does not crash, task is running on background, but no update on taskbar is happening.
Here is the code I created:
package taskbar_test;
import com.sun.glass.ui.Window;
import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import taskbar_test.gen.Xlib_h;
import java.lang.foreign.Arena;
import java.lang.foreign.MemorySegment;
import java.lang.foreign.ValueLayout;
public class AppLinuxXlib extends Application {
@Override
public void start(Stage primaryStage) {
Button startButton = new Button("Start Long Running Task");
startButton.setOnAction(event -> {
final long rawHandle = Window.getWindows().getFirst().getRawHandle();
System.out.println(rawHandle);
// Create a long-running task
Task<Void> longTask = new Task<>() {
@Override
protected Void call() throws Exception {
System.out.println("Started");
try (var arena = Arena.ofConfined()) {
var NET_WM_XAPP_PROGRESS = arena.allocateFrom("NET_WM_XAPP_PROGRESS");
// var NET_WM_XAPP_PROGRESS_PULSE = arena.allocateFrom("NET_WM_XAPP_PROGRESS_PULSE");
MemorySegment x11Session = Xlib_h.XOpenDisplay(MemorySegment.NULL);
System.out.println(x11Session);
// Prepare the progress data
MemorySegment initData = arena.allocateFrom(ValueLayout.JAVA_INT, 0);
Xlib_h.XChangeProperty(x11Session, // display
MemorySegment.ofAddress(rawHandle).address(), // window
NET_WM_XAPP_PROGRESS.address(), // property
6, // type
32, // format
0, // mode PropModeReplace=0
initData, // data
1); // nelements
Xlib_h.XFlush(x11Session);
System.out.println("Countdown started");
// Set the taskbar progress
for (int i = 0; i <= 100; i+=20) {
// Simulate work
Thread.sleep(500);
System.out.println(i);
MemorySegment progressData = arena.allocateFrom(ValueLayout.JAVA_INT, i);
// Update taskbar progress
// https://www.x.org/releases/X11R7.7/doc/libX11/libX11/libX11.html#XChangeProperty
Xlib_h.XChangeProperty(x11Session, // display
MemorySegment.ofAddress(rawHandle).address(), // window
NET_WM_XAPP_PROGRESS.address(), // property
6, // type
32, // format
0, // mode PropModeReplace=0
progressData, // data
1); // nelements
Xlib_h.XFlush(x11Session);
}
System.out.println("Finished");
Xlib_h.XCloseDisplay(x11Session);
} catch (Throwable ex) {
ex.printStackTrace();
}
return null;
}
};
// Start the task in a new thread
new Thread(longTask).start();
});
VBox vbox = new VBox(10, startButton);
Scene scene = new Scene(vbox, 300, 200);
primaryStage.setScene(scene);
primaryStage.setTitle("Taskbar Progress Example Linux");
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
Can someone show me what am I doing wrong and maybe point me to the correct direction with how to make the implementation work?
Thank you very much. Petr
I wasn’t able to solve this, but I suspect it’s because I am running Gnome 43.9 Classic, and I’m not sure it supports showing progress in taskbar buttons. But I can provide some advice, at least:
property argument is an Atom, which is also an XID, not an address or pointer. An Atom must be obtained by passing the atom’s string name to XInternAtom._NET_WM_XAPP_PROGRESS (I don’t understand why there is so little documentation about this property on the web.)With those things in mind, I changed your code to this. (I replaced the taskbar_test.gen.Xlib_h package with explicit calls to java.lang.foreign.)
import com.sun.glass.ui.Window;
import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import java.lang.invoke.MethodHandle;
import java.lang.foreign.Arena;
import java.lang.foreign.MemorySegment;
import java.lang.foreign.ValueLayout;
import java.lang.foreign.Linker;
import java.lang.foreign.SymbolLookup;
import java.lang.foreign.FunctionDescriptor;
public class AppLinuxXlib extends Application {
private static final int None = 0; // from X.h
private static final int False = 0; // from Xlib.h
private static final int PropModeReplace = 0; // from X.h
private static final int XA_CARDINAL = 6; // from Xatom.h
private MethodHandle XOpenDisplay;
private MethodHandle XCloseDisplay;
private MethodHandle XInternAtom;
private MethodHandle XChangeProperty;
private MethodHandle XFlush;
@Override
public void init()
throws Exception {
Linker linker = Linker.nativeLinker();
SymbolLookup lookup = SymbolLookup.loaderLookup();
XOpenDisplay = linker.downcallHandle(
lookup.findOrThrow("XOpenDisplay"),
FunctionDescriptor.of(
ValueLayout.ADDRESS, // returns Display *
ValueLayout.ADDRESS.withName("display_name") // char *display_name
));
XCloseDisplay = linker.downcallHandle(
lookup.findOrThrow("XCloseDisplay"),
FunctionDescriptor.of(
ValueLayout.JAVA_INT, // returns int
ValueLayout.ADDRESS.withName("display") // Display *display
));
XInternAtom = linker.downcallHandle(
lookup.findOrThrow("XInternAtom"),
FunctionDescriptor.of(
ValueLayout.JAVA_INT, // returns Atom
ValueLayout.ADDRESS.withName("display"), // Display *display
ValueLayout.ADDRESS.withName("atom_name"), // char *atom_name
ValueLayout.JAVA_INT.withName("only_if_exists") // Bool only_if_exists
));
XChangeProperty = linker.downcallHandle(
lookup.findOrThrow("XChangeProperty"),
FunctionDescriptor.of(
ValueLayout.JAVA_INT, // returns int
ValueLayout.ADDRESS.withName("display"), // Display *display
ValueLayout.JAVA_INT.withName("w"), // Window w
ValueLayout.JAVA_INT.withName("property"), // Atom property
ValueLayout.JAVA_INT.withName("type"), // Atom type
ValueLayout.JAVA_INT.withName("format"), // int format
ValueLayout.JAVA_INT.withName("mode"), // int mode
ValueLayout.ADDRESS.withName("data"), // char *data
ValueLayout.JAVA_INT.withName("nelements") // int nelements
));
XFlush = linker.downcallHandle(
lookup.findOrThrow("XFlush"),
FunctionDescriptor.of(
ValueLayout.JAVA_INT, // returns int
ValueLayout.ADDRESS.withName("display") // Display *display
));
}
private MemorySegment XOpenDisplay(MemorySegment display)
throws Throwable {
return (MemorySegment) XOpenDisplay.invokeExact(display);
}
private int XCloseDisplay(MemorySegment display)
throws Throwable {
return (int) XCloseDisplay.invokeExact(display);
}
private int XInternAtom(MemorySegment display,
MemorySegment atomName,
int onlyIfExists)
throws Throwable {
return (int) XInternAtom.invokeExact(display, atomName, onlyIfExists);
}
private int XFlush(MemorySegment display)
throws Throwable {
return (int) XFlush.invokeExact(display);
}
private int XChangeProperty(MemorySegment display,
int window,
int property,
int type,
int format,
int mode,
MemorySegment data,
int dataLen)
throws Throwable {
return (int) XChangeProperty.invokeExact(display,
window, property, type, format, mode, data, dataLen);
}
@Override
public void start(Stage primaryStage) {
Button startButton = new Button("Start Long Running Task");
startButton.setOnAction(event -> {
final int window = (int) Window.getWindows().getFirst().getNativeWindow();
System.out.printf("Window=%#x%n", window);
// Create a long-running task
Task<Void> longTask = new Task<>() {
@Override
protected Void call() throws Exception {
System.out.println("Started");
try (var arena = Arena.ofConfined()) {
MemorySegment x11Session = XOpenDisplay(MemorySegment.NULL);
System.out.println("display=" + x11Session);
var name = arena.allocateFrom("_NET_WM_XAPP_PROGRESS");
var NET_WM_XAPP_PROGRESS = XInternAtom(x11Session, name, 0);
if (NET_WM_XAPP_PROGRESS == None) {
throw new RuntimeException("XInternAtom failed.");
}
// var NET_WM_XAPP_PROGRESS_PULSE = arena.allocateFrom("NET_WM_XAPP_PROGRESS_PULSE");
// Prepare the progress data
MemorySegment progressData = arena.allocateFrom(ValueLayout.JAVA_INT, 0);
int status = XChangeProperty(
x11Session, // display
window, // window
NET_WM_XAPP_PROGRESS, // property
XA_CARDINAL, // type
32, // format
PropModeReplace, // mode
progressData, // data
1); // nelements
if (status == False) {
throw new RuntimeException("XChangeProperty returned " + status);
}
status = XFlush(x11Session);
if (status == False) {
throw new RuntimeException("XFlush returned " + status);
}
System.out.println("Countdown started");
// Set the taskbar progress
for (int i = 0; i <= 100; i+=20) {
// Simulate work
Thread.sleep(500);
System.out.println(i);
progressData.set(ValueLayout.JAVA_INT, 0, i);
// Update taskbar progress
// https://www.x.org/releases/X11R7.7/doc/libX11/libX11/libX11.html#XChangeProperty
status = XChangeProperty(
x11Session, // display
window, // window
NET_WM_XAPP_PROGRESS, // property
XA_CARDINAL, // type
32, // format
PropModeReplace, // mode
progressData, // data
1); // nelements
if (status == False) {
throw new RuntimeException("XChangeProperty returned " + status);
}
status = XFlush(x11Session);
if (status == False) {
throw new RuntimeException("XFlush returned " + status);
}
}
System.out.println("Finished");
XCloseDisplay(x11Session);
} catch (Throwable ex) {
ex.printStackTrace();
}
return null;
}
};
// Start the task in a new thread
new Thread(longTask).start();
});
VBox vbox = new VBox(10, startButton);
Scene scene = new Scene(vbox, 300, 200);
primaryStage.setScene(scene);
primaryStage.setTitle("Taskbar Progress Example Linux");
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
This runs, but has no visual effect on my system. I don’t know if that’s because my version of Gnome doesn’t support it. I also tried using the xprop program to set the same window property, and that too had no effect.