1 /* 2 * Copyright (c) 2020, 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 26 package java.lang; 27 28 /** 29 * An inline class implements the {@code NonTearable} interface to 30 * request that the JVM take extra care to avoid structure tearing 31 * when loading or storing any value of the class to a field or array 32 * element. Normally, only fields declared {@code volatile} are 33 * protected against structure tearing, but a class that implements 34 * this marker interface will never have its values torn, even when 35 * they are stored in array elements or in non-{@code volatile} 36 * fields, and even when multiple threads perform racing writes. 37 * 38 * <p> An inline instance of multiple components is said to be "torn" 39 * when two racing threads compete to update those components, and one 40 * thread updates some components while another thread updates other 41 * components. The resulting inline value stored in the heap might be 42 * a hybrid composed of field values from both racing writes. In 43 * extreme cases, this hybrid might be a value which is impossible 44 * to construct by normal means, and if data integrity or security 45 * depends on proper construction, the class should be declared as 46 * implementing {@code NonTearable}. 47 * 48 * <p> Non-inline classes can implement {@code NonTearable}, and 49 * interfaces can extend it, in the usual manner. The special effect 50 * on tearing applies to inline classes which implement this type, 51 * either directly, or indirectly via a supertype. Thus, it is not 52 * correct to assume that an object {@code x} for which {@code x 53 * instanceof NonTearable} is in fact an inline class instance. 54 * It is also not correct to assume that tearing is possible for 55 * classes which do not implement this marker interface, because 56 * the JVM may elect to make some inline values non-tearable if 57 * the cost of doing so is acceptable. The effect of declaring 58 * an inline type {@code NonTearable} is thus to override any 59 * heuristic the JVM may employ to control tearing, in favor 60 * of reliability, and possibly at the expense of performance. 61 * 62 * @author John Rose 63 * @since (valhalla) 64 */ 65 public interface NonTearable { 66 }