ResourceManager.java

/*
 * 練習問題17.4 p.406
 * 刈り取りスレッドを修正して、すべての割り当てられたリソースが開放されるまで、シャットダウンの後も
 * 生き続けるようにしなさい。
 */

package ch17.ex17_04;

import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.util.HashMap;
import java.util.Map;
import javax.naming.Reference;

public final class ResourceManager
{
    final ReferenceQueue<Object> queue;
    // final Map<Reference<?>, Resource> refs; // Original, but error occurs...
    final Map<Reference, Resource> refs;
    final Thread reaper;
    boolean shutdown = false;

    public ResourceManager()
    {
        queue = new ReferenceQueue<Object>();
        // refs = new HashMap<Reference<?>, Resource>(); // Original, but error occurs...
        refs = new HashMap<Reference, Resource>();
        reaper = new ReaperThread();
        reaper.start();

        // ...リソースの初期化...
    }

    public synchronized void shutdown()
    {
        if (!shutdown)
        {
            shutdown = true;
            reaper.interrupt();
        }
    }

    public synchronized Resource getResource(Object key)
    {
        if (shutdown)
        {
            throw new IllegalStateException();
        }
        Resource res = new ResourceImpl(key);
        // Reference<?> ref = new PhantomReference<Object>(key, queue); // Original. but error occurs...
        Reference ref = new PhantomReference<Object>(key, queue);
        refs.put(ref, res);
        return res;
    }

    class ReaperThread extends Thread
    {
        public void run()
        {
            // 割り込まれるまで実行
            while (true)
            {
                try
                {
                    Reference<?> ref = queue.remove();
                    Resource res = null;
                    synchronized(ResourceManager.this)
                    {
                        res = refs.get(ref);
                        refs.remove(ref);
                    }
                    res.release();
                    ref.clear();
                }
                catch (InterruptedException ex)
                {
                    break; // すべて終了
                }
            }
        }
    }
}