1 /* 2 * Copyright (c) 2010, 2011, 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.invoke; 27 28 // Android-changed: removed references to MutableCallSite.syncAll(). 29 /** 30 * A {@code VolatileCallSite} is a {@link CallSite} whose target acts like a volatile variable. 31 * An {@code invokedynamic} instruction linked to a {@code VolatileCallSite} sees updates 32 * to its call site target immediately, even if the update occurs in another thread. 33 * There may be a performance penalty for such tight coupling between threads. 34 * <p> 35 * In other respects, a {@code VolatileCallSite} is interchangeable 36 * with {@code MutableCallSite}. 37 * @see MutableCallSite 38 * @author John Rose, JSR 292 EG 39 */ 40 public class VolatileCallSite extends CallSite { 41 /** 42 * Creates a call site with a volatile binding to its target. 43 * The initial target is set to a method handle 44 * of the given type which will throw an {@code IllegalStateException} if called. 45 * @param type the method type that this call site will have 46 * @throws NullPointerException if the proposed type is null 47 */ 48 public VolatileCallSite(MethodType type) { 49 super(type); 50 } 51 52 /** 53 * Creates a call site with a volatile binding to its target. 54 * The target is set to the given value. 55 * @param target the method handle that will be the initial target of the call site 56 * @throws NullPointerException if the proposed target is null 57 */ 58 public VolatileCallSite(MethodHandle target) { 59 super(target); 60 } 61 62 /** 63 * Returns the target method of the call site, which behaves 64 * like a {@code volatile} field of the {@code VolatileCallSite}. 65 * <p> 66 * The interactions of {@code getTarget} with memory are the same 67 * as of a read from a {@code volatile} field. 68 * <p> 69 * In particular, the current thread is required to issue a fresh 70 * read of the target from memory, and must not fail to see 71 * a recent update to the target by another thread. 72 * 73 * @return the linkage state of this call site, a method handle which can change over time 74 * @see #setTarget 75 */ 76 @Override public final MethodHandle getTarget() { 77 return getTargetVolatile(); 78 } 79 80 /** 81 * Updates the target method of this call site, as a volatile variable. 82 * The type of the new target must agree with the type of the old target. 83 * <p> 84 * The interactions with memory are the same as of a write to a volatile field. 85 * In particular, any threads is guaranteed to see the updated target 86 * the next time it calls {@code getTarget}. 87 * @param newTarget the new target 88 * @throws NullPointerException if the proposed new target is null 89 * @throws WrongMethodTypeException if the proposed new target 90 * has a method type that differs from the previous target 91 * @see #getTarget 92 */ 93 @Override public void setTarget(MethodHandle newTarget) { 94 checkTargetChange(getTargetVolatile(), newTarget); 95 setTargetVolatile(newTarget); 96 } 97 98 /** 99 * {@inheritDoc} 100 */ 101 @Override 102 public final MethodHandle dynamicInvoker() { 103 return makeDynamicInvoker(); 104 } 105 } 106
