JFrame永远不会被垃圾收集

Question

我有一个需要打开多个JFrame的应用程序(它是一个日志查看器,有时您需要在单独的窗口中查看一堆日志来进行比较).

似乎JVM(OS X上的Java 8更新101)持有对JFrame的强引用,这阻止了它被垃圾收集,并最终导致抛出OutOfMemoryError.

若要查看该问题,请运行此问题,最大堆大小为200 MB.每次打开一个窗口时,它都会消耗50兆字节的RAM.打开三个窗口(使用150兆字节的RAM).然后关闭三个窗口(调用dispose),这将释放内存.然后尝试打开第四个窗口.抛出OutOfMemoryError,第四个窗口无法打开.

我已经看到了其他答案,说明在必要时会自动释放内存以避免耗尽,但这似乎并没有发生.

package com.prosc.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;

public class WindowLeakTest {
    public static void main(String[] args) {
        EventQueue.invokeLater( new Runnable() {
            public void run() {
                JFrame launcherWindow = new JFrame( "Launcher window" );
                JButton launcherButton = new JButton( "Open new JFrame" );
                launcherButton.addActionListener( new ActionListener() {
                    public void actionPerformed( ActionEvent e ) {
                        JFrame subFrame = new JFrame( "Sub frame" ) {
                            private byte[] bigMemoryChunk = new byte[ 50 * 1024 * 1024 ]; //50 megabytes of memory

                            protected void finalize() throws Throwable {
                                System.out.println("Finalizing window (Never called until after OutOfMemory is thrown)");
                                super.finalize();
                            }
                        };
                        subFrame.setDefaultCloseOperation( WindowConstants.DISPOSE_ON_CLOSE );
                        subFrame.add( new JLabel( "Nothing to see here" ) );
                        subFrame.pack();
                        subFrame.setVisible( true );
                        System.out.println( "Memory usage after new window: " + getMemoryInfo() );
                    }
                } );
                launcherWindow.add( launcherButton );
                launcherWindow.pack();
                launcherWindow.setVisible( true );

                new Timer( 5000, new ActionListener() {
                    public void actionPerformed( ActionEvent e ) {
                        System.gc();
                        System.out.println( "Current memory usage after garbage collection: " + getMemoryInfo() );
                    }
                } ).start();
            }
        } );
    }

    public static String getMemoryInfo() {
        NumberFormat numberFormat = NumberFormat.getNumberInstance();
        return "Max heap size is " + numberFormat.format( Runtime.getRuntime().maxMemory() ) + "; free memory is " + numberFormat.format( Runtime.getRuntime().freeMemory() ) + "; total memory is " + numberFormat.format( Runtime.getRuntime().totalMemory() );
    }
}

Answer 1

如所示在这里,存在由于与一个典型的主机对等组件不可恢复的分配一个不可约泄漏.在创建和处理~10 ^3个窗口的过程中剩余约2 MB .在您的情况下,主要的泄漏是由于保留的实例bigMemoryChunk.一种方法是让这些实例不可达的WindowListener.

this.addWindowListener(new WindowAdapter() {

    @Override
    public void windowClosing(WindowEvent e) {
        bigMemoryChunk = null;
    }
});

我们为什么需要设置bigMemoryChunk = null？

JFrame没有直接的方法来知道程序中的每个实例都有一个关联的实例bigMemoryChunk.当这个对象不可访问时,它就有资格进行垃圾收集; bigMemoryChunk在这种情况下,它是对数组对象的唯一引用,因此将其设置为null使其立即有资格进行以后的垃圾回收.

如果JFrame是唯一拿着参考bigMemoryChunk......那么为什么不JFrame和bigMemoryChunk...窗口已被释放后,都得到垃圾收集？

您可能会产生混淆遏制与继承和组成.在JFrame不是"保持一参考bigMemoryChunk;" 所述JFrame 具有命名实例变量bigMemoryChunk保存到数组对象的引用.丢失给帧的对等体的少量内存由主机拥有和管理.大量的记忆bigMemoryChunk是你的计划的责任.随附WindowListener允许您将数组对象的管理与关闭框架相关联.

下面的配置文件显示了一系列打开的四个子帧; 然后关闭每个,然后在分析器中进行强制垃圾收集.

如异形:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.text.NumberFormat;

public class WindowLeakTest {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame launcherWindow = new JFrame("Launcher window");
                launcherWindow.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                JButton launcherButton = new JButton("Open new JFrame");
                launcherButton.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        JFrame subFrame = new JFrame("Sub frame") {
                            private byte[] bigMemoryChunk = new byte[50 * 1024 * 1024];

                            {
                                this.addWindowListener(new WindowAdapter() {

                                    @Override
                                    public void windowClosing(WindowEvent e) {
                                        bigMemoryChunk = null;
                                    }
                                });
                            }

                            @Override
                            protected void finalize() throws Throwable {
                                super.finalize();
                                System.out.println("Finalizing window.");
                            }
                        };
                        subFrame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
                        subFrame.add(new JLabel("Nothing to see here"));
                        subFrame.pack();
                        subFrame.setVisible(true);
                    }
                });
                launcherWindow.add(launcherButton);
                launcherWindow.pack();
                launcherWindow.setVisible(true);
            }
        });
    }
}