在 JavaFX 应用程序线程以外的线程上进行 ImageIO 调用的 JavaFX 应用程序在 Mac OS X 上挂起

Question

假设我有一个示例 JavaFX 应用程序，它使用从应用程序的 JAR 中读取的图像来更新其 UI，并且以延迟的方式执行此操作(即图像是在之后绘制的) > 显示 UI):

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);
    }
}

上面的代码工作正常。现在，考虑我想在单独的线程中加载图像并在 JavaFX 应用程序线程上处理结果，因此我将重写代码如下:

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);
    }
}

重写的代码在 Linux 和 Windows 上都能正常工作，但在 Mac OS X 10.14.5(Mojave)上挂起em>)、Oracle JDK 1.8.0_192 以及 JetBrains Runtime 1.8.0_202。

部分线程转储是:

"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)

所以这看起来像是某种竞争条件。有趣的是，类似的 JFC/Swing 应用程序根本不会挂起。

我第一次遇到这种行为是在 Kotlin 中使用协程时。例如，this code this one 时不会挂起确实如此。

问题:

1. 谁能解释一下上述行为？我是否有可能错过某些东西而不是看到 JDK 中的错误？
2. 如何进一步诊断问题？

Answer 1

我正在编写一个应用程序，需要在单独的线程上延迟加载图像缩略图。 ImageIO.read() 也挂起。但有人建议这样做

new BufferedImage(1, 1, BufferedImage.TYPE_INT_RGB);

在启动其他线程之前在主应用程序线程中运行，因为这显然会导致 AWT 第一次运行一些必须在主线程中完成的初始化代码。这解决了 ImageIO.read 问题。

但是调用时也挂了

SwingFXUtils.toFXImage(bufferedImage, null);

所以我把它移到了我的“Platform.runLater(...)”调用中，以便它可以在 JavaFX 线程上完成，并且这有效，尽管它并不理想，因为我希望发生这种转换在单独的线程上，因此 UI 的响应速度会更快。但这种转换发生在内存中，所以我可以忍受它。