1 /* 2 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package jdk.internal.misc; 26 27 import java.util.Collection; 28 import java.util.HashSet; 29 30 /** 31 * A thread-local variable that is notified when a thread terminates and 32 * it has been initialized in the terminating thread (even if it was 33 * initialized with a null value). 34 */ 35 public class JdkThreadLocal<T> extends ThreadLocal<T> { 36 37 @Override 38 protected final T initialValue() { 39 T value = computeInitialValue(); 40 REGISTRY.get().add(this); 41 return value; 42 } 43 44 @Override 45 public void set(T value) { 46 super.set(value); 47 REGISTRY.get().add(this); 48 } 49 50 @Override 51 public void remove() { 52 super.remove(); 53 REGISTRY.get().remove(this); 54 } 55 56 /** 57 * Just like {@link ThreadLocal#initialValue()} but subclasses of {@link JdkThreadLocal} 58 * must override this method instead as {@link #initialValue()} is final. 59 * 60 * @return the initial value for this thread-local 61 */ 62 protected T computeInitialValue() { 63 return null; 64 } 65 66 /** 67 * Invoked by a thread when terminating and this thread-local has an associated 68 * value for the terminating thread (even if that value is null), so that any 69 * native resources maintained by the value can be released. 70 */ 71 protected void threadTerminated() { 72 } 73 74 // following method and field are implementation details and should only be 75 // called from the corresponding code int Thread class. 76 77 /** 78 * Invokes the JdkThreadLocal's threadTerminated method on all instances of 79 * given collection. 80 */ 81 public static void threadTerminated(Collection<JdkThreadLocal<?>> jdkTls) { 82 if (jdkTls != null) { 83 for (JdkThreadLocal<?> jdkTl : jdkTls) { 84 jdkTl.threadTerminated(); 85 } 86 } 87 } 88 89 /** 90 * a per-thread registry of JdkThreadLocal(s) that have been initialized 91 * in a particular thread. 92 */ 93 public static final ThreadLocal<Collection<JdkThreadLocal<?>>> REGISTRY = 94 new ThreadLocal<>() { 95 @Override 96 protected Collection<JdkThreadLocal<?>> initialValue() { 97 return new HashSet<>(4); 98 } 99 }; 100 }