问题
Consider I have a sample JavaFX application which updates its UI with an image read from the application's JAR, and does so in a delayed manner (i.e. the image is painted after the UI is shown):
import javafx.application.Application;
import javafx.application.Platform;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.image.ImageView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
public final class SameThreadAsync extends Application {
@Override
public void start(final Stage primaryStage) {
final ImageView imageView = new ImageView();
imageView.setPreserveRatio(true);
imageView.setSmooth(true);
imageView.setFitWidth(300.0);
imageView.setFitHeight(300.0);
Platform.runLater(() -> {
final BufferedImage image = getIcon();
imageView.setImage(SwingFXUtils.toFXImage(image, null));
});
final Node label = new Label(null, imageView);
final StackPane root = new StackPane();
root.getChildren().add(label);
primaryStage.setScene(new Scene(root, 300.0, 300.0));
primaryStage.show();
}
private BufferedImage getIcon() {
System.out.println("Reading an image from thread " + Thread.currentThread().getName());
try (final InputStream in = new BufferedInputStream(getClass().getResourceAsStream("logo1.png"))) {
return ImageIO.read(in);
} catch (final IOException ioe) {
ioe.printStackTrace();
return new BufferedImage(0, 0, BufferedImage.TYPE_INT_ARGB);
}
}
public static void main(final String ... args) {
launch(args);
}
}
The above code works fine. Now, consider I want to load the image in a separate thread and process the result on the JavaFX Application Thread, so I'll rewrite the code as follows:
import javafx.application.Application;
import javafx.application.Platform;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.image.ImageView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public final class SeparateThreadAsync extends Application {
private static final ExecutorService IO_EXECUTOR = Executors.newSingleThreadExecutor(r -> new Thread(r, "I/O Queue"));
@Override
public void start(final Stage primaryStage) {
final ImageView imageView = new ImageView();
imageView.setPreserveRatio(true);
imageView.setSmooth(true);
imageView.setFitWidth(300.0);
imageView.setFitHeight(300.0);
IO_EXECUTOR.submit(() -> {
final BufferedImage image = getIcon();
Platform.runLater(() -> imageView.setImage(SwingFXUtils.toFXImage(image, null)));
});
final Node label = new Label(null, imageView);
final StackPane root = new StackPane();
root.getChildren().add(label);
primaryStage.setScene(new Scene(root, 300.0, 300.0));
primaryStage.show();
}
private BufferedImage getIcon() {
System.out.println("Reading an image from thread " + Thread.currentThread().getName());
try (final InputStream in = new BufferedInputStream(getClass().getResourceAsStream("logo1.png"))) {
return ImageIO.read(in);
} catch (final IOException ioe) {
ioe.printStackTrace();
return new BufferedImage(0, 0, BufferedImage.TYPE_INT_ARGB);
}
}
public static void main(final String ... args) {
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
IO_EXECUTOR.shutdown();
System.out.println("I/O Queue shut down.");
}));
launch(args);
}
}
The rewritten code works fine on both Linux and Windows but hangs on Mac OS X 10.14.5 (Mojave), Oracle JDK 1.8.0_192 and also JetBrains Runtime 1.8.0_202.
The partial thread dump is:
"I/O Queue" #19 prio=5 os_prio=31 tid=0x00007ffe3d85a000 nid=0x12007 runnable [0x0000700004822000]
java.lang.Thread.State: RUNNABLE
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)
- locked <0x000000076ab068a8> (a java.util.Vector)
- locked <0x000000076ab06900> (a java.util.Vector)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1824)
at java.lang.Runtime.load0(Runtime.java:809)
- locked <0x000000076ab1dea8> (a java.lang.Runtime)
at java.lang.System.load(System.java:1086)
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)
- locked <0x000000076ab068a8> (a java.util.Vector)
- locked <0x000000076ab06900> (a java.util.Vector)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1845)
at java.lang.Runtime.loadLibrary0(Runtime.java:870)
- locked <0x000000076ab1dea8> (a java.lang.Runtime)
at java.lang.System.loadLibrary(System.java:1122)
at java.awt.Toolkit$3.run(Toolkit.java:1636)
at java.awt.Toolkit$3.run(Toolkit.java:1634)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.Toolkit.loadLibraries(Toolkit.java:1633)
at java.awt.Toolkit.<clinit>(Toolkit.java:1670)
at sun.awt.AppContext$2.run(AppContext.java:277)
at sun.awt.AppContext$2.run(AppContext.java:266)
at java.security.AccessController.doPrivileged(Native Method)
at sun.awt.AppContext.initMainAppContext(AppContext.java:266)
at sun.awt.AppContext.access$400(AppContext.java:135)
at sun.awt.AppContext$3.run(AppContext.java:321)
- locked <0x000000076c238c00> (a sun.awt.AppContext$GetAppContextLock)
at sun.awt.AppContext$3.run(AppContext.java:304)
at java.security.AccessController.doPrivileged(Native Method)
at sun.awt.AppContext.getAppContext(AppContext.java:303)
at javax.imageio.spi.IIORegistry.getDefaultInstance(IIORegistry.java:154)
at javax.imageio.ImageIO.<clinit>(ImageIO.java:66)
at com.example.SeparateThreadAsync.getIcon(SeparateThreadAsync.java:49)
at com.example.SeparateThreadAsync.lambda$start$2(SeparateThreadAsync.java:33)
at com.example.SeparateThreadAsync$$Lambda$61/1820086024.run(Unknown Source)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
"JavaFX Application Thread" #15 prio=5 os_prio=31 tid=0x00007ffe3b0e4000 nid=0x307 waiting for monitor entry [0x00007ffee75f1000]
java.lang.Thread.State: BLOCKED (on object monitor)
at java.lang.Runtime.load0(Runtime.java:801)
- waiting to lock <0x000000076ab1dea8> (a java.lang.Runtime)
at java.lang.System.load(System.java:1086)
at com.sun.glass.utils.NativeLibLoader.loadLibraryFullPath(NativeLibLoader.java:201)
at com.sun.glass.utils.NativeLibLoader.loadLibraryInternal(NativeLibLoader.java:94)
at com.sun.glass.utils.NativeLibLoader.loadLibrary(NativeLibLoader.java:39)
- locked <0x000000076b4185c0> (a java.lang.Class for com.sun.glass.utils.NativeLibLoader)
at com.sun.javafx.font.PrismFontFactory.lambda$static$244(PrismFontFactory.java:100)
at com.sun.javafx.font.PrismFontFactory$$Lambda$70/1988937384.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.font.PrismFontFactory.<clinit>(PrismFontFactory.java:98)
at com.sun.javafx.text.PrismTextLayout.<clinit>(PrismTextLayout.java:67)
at com.sun.javafx.text.PrismTextLayoutFactory.<clinit>(PrismTextLayoutFactory.java:33)
at com.sun.javafx.tk.quantum.QuantumToolkit.getTextLayoutFactory(QuantumToolkit.java:1086)
at com.sun.javafx.scene.control.skin.Utils.<clinit>(Utils.java:90)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at com.sun.javafx.css.StyleManager.getURL(StyleManager.java:863)
at com.sun.javafx.css.StyleManager.loadStylesheetUnPrivileged(StyleManager.java:1075)
- locked <0x000000076c3bc948> (a java.lang.Object)
at com.sun.javafx.css.StyleManager.loadStylesheet(StyleManager.java:935)
at com.sun.javafx.css.StyleManager._setDefaultUserAgentStylesheet(StyleManager.java:1395)
- locked <0x000000076c3bc948> (a java.lang.Object)
at com.sun.javafx.css.StyleManager.setUserAgentStylesheets(StyleManager.java:1227)
- locked <0x000000076c3bc948> (a java.lang.Object)
at com.sun.javafx.application.PlatformImpl.lambda$_setPlatformUserAgentStylesheet$181(PlatformImpl.java:698)
at com.sun.javafx.application.PlatformImpl$$Lambda$65/566730701.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl._setPlatformUserAgentStylesheet(PlatformImpl.java:697)
at com.sun.javafx.application.PlatformImpl.setPlatformUserAgentStylesheet(PlatformImpl.java:548)
at com.sun.javafx.application.PlatformImpl.setDefaultPlatformUserAgentStylesheet(PlatformImpl.java:512)
at javafx.scene.control.Control.<clinit>(Control.java:87)
at com.example.SeparateThreadAsync.start(SeparateThreadAsync.java:37)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
at com.sun.javafx.application.LauncherImpl$$Lambda$56/1315653396.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/1212899836.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$49/1963951195.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/1289696681.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
so it seems like some sort of a race condition. Interestingly, a similar JFC/Swing application doesn't hang at all.
I first encountered this behaviour while playing with coroutines in Kotlin. For example, this code doesn't hang while this one does.
Questions:
- Can anyone explain the above behaviour? Is there any chance I'm missing something rather than seeing a bug in the JDK?
- How can I further diagnose the problem?
回答1:
The above behaviour seems to be a bug in the Mac OS X implementation of Oracle JDK -- the problem shows up only with Java 1.8.0, I was unable to reproduce it against either Java 9.0.4 or 10.0.2.
来源：https://stackoverflow.com/questions/56395318/javafx-application-with-an-imageio-call-on-a-thread-other-than-javafx-applicatio