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/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */ package java.lang.ref; import java.security.PrivilegedAction; import java.security.AccessController; import sun.misc.JavaLangAccess; import sun.misc.SharedSecrets; import sun.misc.VM; final class Finalizer extends FinalReference { /* Package-private; must be in same package as the Reference class */ private static ReferenceQueue queue = new ReferenceQueue<>(); private static Finalizer unfinalized = null; private static final Object lock = new Object(); private Finalizer next = null, prev = null; private boolean hasBeenFinalized() { return (next == this); } private void add() { synchronized (lock) { if (unfinalized != null) { this.next = unfinalized; unfinalized.prev = this; } unfinalized = this; } } private void remove() { synchronized (lock) { if (unfinalized == this) { if (this.next != null) { unfinalized = this.next; } else { unfinalized = this.prev; } } if (this.next != null) { this.next.prev = this.prev; } if (this.prev != null) { this.prev.next = this.next; } this.next = this; /* Indicates that this has been finalized */ this.prev = this; } } private Finalizer(Object finalizee) { super(finalizee, queue); add(); } /* Invoked by VM */ static void register(Object finalizee) { new Finalizer(finalizee); } private void runFinalizer(JavaLangAccess jla) { synchronized (this) { if (hasBeenFinalized()) return; remove(); } try { Object finalizee = this.get(); if (finalizee != null && !(finalizee instanceof java.lang.Enum)) { jla.invokeFinalize(finalizee); /* Clear stack slot containing this variable, to decrease the chances of false retention with a conservative GC */ finalizee = null; } } catch (Throwable x) { } super.clear(); } /* Create a privileged secondary finalizer thread in the system thread group for the given Runnable, and wait for it to complete. This method is used by both runFinalization and runFinalizersOnExit. The former method invokes all pending finalizers, while the latter invokes all uninvoked finalizers if on-exit finalization has been enabled. These two methods could have been implemented by offloading their work to the regular finalizer thread and waiting for that thread to finish. The advantage of creating a fresh thread, however, is that it insulates invokers of these methods from a stalled or deadlocked finalizer thread. */ private static void forkSecondaryFinalizer(final Runnable proc) { AccessController.doPrivileged( new PrivilegedAction() { public Void run() { ThreadGroup tg = Thread.currentThread().getThreadGroup(); for (ThreadGroup tgn = tg; tgn != null; tg = tgn, tgn = tg.getParent()); Thread sft = new Thread(tg, proc, "Secondary finalizer"); sft.start(); try { sft.join(); } catch (InterruptedException x) { /* Ignore */ } return null; }}); } /* Called by Runtime.runFinalization() */ static void runFinalization() { if (!VM.isBooted()) { return; } forkSecondaryFinalizer(new Runnable() { private volatile boolean running; public void run() { if (running) return; final JavaLangAccess jla = SharedSecrets.getJavaLangAccess(); running = true; for (;;) { Finalizer f = (Finalizer)queue.poll(); if (f == null) break; f.runFinalizer(jla); } } }); } /* Invoked by java.lang.Shutdown */ static void runAllFinalizers() { if (!VM.isBooted()) { return; } forkSecondaryFinalizer(new Runnable() { private volatile boolean running; public void run() { if (running) return; final JavaLangAccess jla = SharedSecrets.getJavaLangAccess(); running = true; for (;;) { Finalizer f; synchronized (lock) { f = unfinalized; if (f == null) break; unfinalized = f.next; } f.runFinalizer(jla); }}}); } private static class FinalizerThread extends Thread { private volatile boolean running; FinalizerThread(ThreadGroup g) { super(g, "Finalizer"); } public void run() { if (running) return; // Finalizer thread starts before System.initializeSystemClass // is called. Wait until JavaLangAccess is available while (!VM.isBooted()) { // delay until VM completes initialization try { VM.awaitBooted(); } catch (InterruptedException x) { // ignore and continue } } final JavaLangAccess jla = SharedSecrets.getJavaLangAccess(); running = true; for (;;) { try { Finalizer f = (Finalizer)queue.remove(); f.runFinalizer(jla); } catch (InterruptedException x) { // ignore and continue } } } } static { ThreadGroup tg = Thread.currentThread().getThreadGroup(); for (ThreadGroup tgn = tg; tgn != null; tg = tgn, tgn = tg.getParent()); Thread finalizer = new FinalizerThread(tg); finalizer.setPriority(Thread.MAX_PRIORITY - 2); finalizer.setDaemon(true); finalizer.start(); } }