1*cdf0e10cSrcweir /************************************************************************* 2*cdf0e10cSrcweir * 3*cdf0e10cSrcweir * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4*cdf0e10cSrcweir * 5*cdf0e10cSrcweir * Copyright 2000, 2010 Oracle and/or its affiliates. 6*cdf0e10cSrcweir * 7*cdf0e10cSrcweir * OpenOffice.org - a multi-platform office productivity suite 8*cdf0e10cSrcweir * 9*cdf0e10cSrcweir * This file is part of OpenOffice.org. 10*cdf0e10cSrcweir * 11*cdf0e10cSrcweir * OpenOffice.org is free software: you can redistribute it and/or modify 12*cdf0e10cSrcweir * it under the terms of the GNU Lesser General Public License version 3 13*cdf0e10cSrcweir * only, as published by the Free Software Foundation. 14*cdf0e10cSrcweir * 15*cdf0e10cSrcweir * OpenOffice.org is distributed in the hope that it will be useful, 16*cdf0e10cSrcweir * but WITHOUT ANY WARRANTY; without even the implied warranty of 17*cdf0e10cSrcweir * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18*cdf0e10cSrcweir * GNU Lesser General Public License version 3 for more details 19*cdf0e10cSrcweir * (a copy is included in the LICENSE file that accompanied this code). 20*cdf0e10cSrcweir * 21*cdf0e10cSrcweir * You should have received a copy of the GNU Lesser General Public License 22*cdf0e10cSrcweir * version 3 along with OpenOffice.org. If not, see 23*cdf0e10cSrcweir * <http://www.openoffice.org/license.html> 24*cdf0e10cSrcweir * for a copy of the LGPLv3 License. 25*cdf0e10cSrcweir * 26*cdf0e10cSrcweir ************************************************************************/ 27*cdf0e10cSrcweir 28*cdf0e10cSrcweir package util; 29*cdf0e10cSrcweir 30*cdf0e10cSrcweir import java.lang.ref.PhantomReference; 31*cdf0e10cSrcweir import java.lang.ref.ReferenceQueue; 32*cdf0e10cSrcweir 33*cdf0e10cSrcweir /** 34*cdf0e10cSrcweir * Wait until an object has become unreachable. 35*cdf0e10cSrcweir * 36*cdf0e10cSrcweir * <p>Instances of this class will typically be used as either:</p> 37*cdf0e10cSrcweir * <pre> 38*cdf0e10cSrcweir * SomeType o = new SomeType(...); 39*cdf0e10cSrcweir * ... // use "o" 40*cdf0e10cSrcweir * WaitUnreachable u = new WaitUnreachable(o); 41*cdf0e10cSrcweir * o = null; 42*cdf0e10cSrcweir * u.waitUnreachable(); 43*cdf0e10cSrcweir * </pre> 44*cdf0e10cSrcweir * <p>or:</p> 45*cdf0e10cSrcweir * <pre> 46*cdf0e10cSrcweir * WaitUnreachable u = new WaitUnreachable(new SomeType(...)); 47*cdf0e10cSrcweir * ... // use "(SomeType) u.get()" 48*cdf0e10cSrcweir * u.waitUnreachable(); 49*cdf0e10cSrcweir * </pre> 50*cdf0e10cSrcweir */ 51*cdf0e10cSrcweir public final class WaitUnreachable { 52*cdf0e10cSrcweir /** 53*cdf0e10cSrcweir * Creates a new waiter. 54*cdf0e10cSrcweir * 55*cdf0e10cSrcweir * @param obj the object on which to wait 56*cdf0e10cSrcweir */ 57*cdf0e10cSrcweir public WaitUnreachable(Object obj) { 58*cdf0e10cSrcweir this.obj = obj; 59*cdf0e10cSrcweir queue = new ReferenceQueue(); 60*cdf0e10cSrcweir ref = new PhantomReference(obj, queue); 61*cdf0e10cSrcweir } 62*cdf0e10cSrcweir 63*cdf0e10cSrcweir /** 64*cdf0e10cSrcweir * Gets the object on which to wait. 65*cdf0e10cSrcweir * 66*cdf0e10cSrcweir * @return the object on which to wait, or <code>null</code> if 67*cdf0e10cSrcweir * <code>waitUnreachable</code> has already been called 68*cdf0e10cSrcweir */ 69*cdf0e10cSrcweir public synchronized Object get() { 70*cdf0e10cSrcweir return obj; 71*cdf0e10cSrcweir } 72*cdf0e10cSrcweir 73*cdf0e10cSrcweir /** 74*cdf0e10cSrcweir * Starts waiting for the object to become unreachable. 75*cdf0e10cSrcweir * 76*cdf0e10cSrcweir * <p>This blocks the current thread until the object has become 77*cdf0e10cSrcweir * unreachable.</p> 78*cdf0e10cSrcweir * 79*cdf0e10cSrcweir * <p>Actually, this method waits until the JVM has <em>detected</em> that 80*cdf0e10cSrcweir * the object has become unreachable. This is not deterministic, but this 81*cdf0e10cSrcweir * methods makes a best effort to cause the JVM to eventually detect the 82*cdf0e10cSrcweir * situation. With a typical JVM, this should suffice.</p> 83*cdf0e10cSrcweir */ 84*cdf0e10cSrcweir public void waitUnreachable() { 85*cdf0e10cSrcweir synchronized (this) { 86*cdf0e10cSrcweir obj = null; 87*cdf0e10cSrcweir } 88*cdf0e10cSrcweir System.out.println("waiting for gc"); 89*cdf0e10cSrcweir while (queue.poll() == null) { 90*cdf0e10cSrcweir System.gc(); 91*cdf0e10cSrcweir System.runFinalization(); 92*cdf0e10cSrcweir byte[] dummy = new byte[1024]; 93*cdf0e10cSrcweir } 94*cdf0e10cSrcweir } 95*cdf0e10cSrcweir 96*cdf0e10cSrcweir /** 97*cdf0e10cSrcweir * Ensures that an object will be finalized as soon as possible. 98*cdf0e10cSrcweir * 99*cdf0e10cSrcweir * <p>This does not block the current thread. Instead, a new thread is 100*cdf0e10cSrcweir * spawned that busy waits for the given object to become unreachable.</p> 101*cdf0e10cSrcweir * 102*cdf0e10cSrcweir * <p>This method cannot guarantee that the given object is eventually 103*cdf0e10cSrcweir * finalized, but it makes a best effort. With a typical JVM, this should 104*cdf0e10cSrcweir * suffice.</p> 105*cdf0e10cSrcweir * 106*cdf0e10cSrcweir * @param obj the object of which to ensure finalization 107*cdf0e10cSrcweir */ 108*cdf0e10cSrcweir public static void ensureFinalization(final Object obj) { 109*cdf0e10cSrcweir final class WaitThread extends Thread { 110*cdf0e10cSrcweir public WaitThread(Object obj) { 111*cdf0e10cSrcweir super("ensureFinalization"); 112*cdf0e10cSrcweir unreachable = new WaitUnreachable(obj); 113*cdf0e10cSrcweir } 114*cdf0e10cSrcweir 115*cdf0e10cSrcweir public void run() { 116*cdf0e10cSrcweir unreachable.waitUnreachable(); 117*cdf0e10cSrcweir } 118*cdf0e10cSrcweir 119*cdf0e10cSrcweir private final WaitUnreachable unreachable; 120*cdf0e10cSrcweir }; 121*cdf0e10cSrcweir new WaitThread(obj).start(); 122*cdf0e10cSrcweir } 123*cdf0e10cSrcweir 124*cdf0e10cSrcweir private Object obj; 125*cdf0e10cSrcweir private final ReferenceQueue queue; 126*cdf0e10cSrcweir private final PhantomReference ref; 127*cdf0e10cSrcweir } 128