test/036-finalizer/src/Main.java

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;

/**
 * Some finalizer tests.
 *
 * This only works if System.runFinalization() causes finalizers to run
 * immediately or very soon.
 */
public class Main {
    private static void snooze(int ms) {
        try {
            Thread.sleep(ms);
        } catch (InterruptedException ie) {
            System.out.println("Snooze: " + ie.getMessage());
        }
    }

    public static WeakReference<FinalizerTest> makeRef() {
        /*
         * Make ft in another thread, so there is no danger of
         * a conservative reference leaking onto the main thread's
         * stack.
         */

        final List<WeakReference<FinalizerTest>> wimp =
                new ArrayList<WeakReference<FinalizerTest>>();
        Thread t = new Thread() {
                public void run() {
                    FinalizerTest ft = new FinalizerTest("wahoo");
                    wimp.add(new WeakReference<FinalizerTest>(ft));
                    ft = null;
                }
            };

        t.start();

        try {
            t.join();
        } catch (InterruptedException ie) {
            throw new RuntimeException(ie);
        }

        return wimp.get(0);
    }

    public static String wimpString(final WeakReference<FinalizerTest> wimp) {
        /*
         * Do the work in another thread, so there is no danger of a
         * conservative reference to ft leaking onto the main thread's
         * stack.
         */

        final String[] s = new String[1];
        Thread t = new Thread() {
                public void run() {
                    FinalizerTest ref = wimp.get();
                    if (ref != null) {
                        s[0] = ref.toString();
                    }
                }
            };

        t.start();

        try {
            t.join();
        } catch (InterruptedException ie) {
            throw new RuntimeException(ie);
        }

        return s[0];
    }

    public static void main(String[] args) {
        WeakReference<FinalizerTest> wimp = makeRef();

        System.out.println("wimp: " + wimpString(wimp));

        /* this will try to collect and finalize ft */
        System.out.println("gc");
        Runtime.getRuntime().gc();

        System.out.println("wimp: " + wimpString(wimp));
        System.out.println("finalize");
        System.runFinalization();
        System.out.println("wimp: " + wimpString(wimp));

        System.out.println("sleep");
        snooze(1000);

        System.out.println("reborn: " + FinalizerTest.mReborn);
        System.out.println("wimp: " + wimpString(wimp));
        System.out.println("reset reborn");
        Runtime.getRuntime().gc();
        FinalizerTest.mReborn = FinalizerTest.mNothing;
        System.out.println("gc + finalize");
        System.gc();
        System.runFinalization();

        System.out.println("sleep");
        snooze(1000);

        System.out.println("reborn: " + FinalizerTest.mReborn);
        System.out.println("wimp: " + wimpString(wimp));
    }

    public static class FinalizerTest {
        public static FinalizerTest mNothing = new FinalizerTest("nothing");
        public static FinalizerTest mReborn = mNothing;

        private final String message;
        private boolean finalized = false;

        public FinalizerTest(String message) {
            this.message = message;
        }

        public String toString() {
            return "[FinalizerTest message=" + message +
                    ", finalized=" + finalized + "]";
        }

        protected void finalize() {
            finalized = true;
            mReborn = this;
        }
    }
}