--- a/jdk/src/share/classes/java/dyn/MutableCallSite.java Wed Jul 05 17:38:31 2017 +0200
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,282 +0,0 @@
-/*
- * Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation. Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-package java.dyn;
-
-import sun.dyn.*;
-import sun.dyn.empty.Empty;
-import java.util.concurrent.atomic.AtomicInteger;
-
-/**
- * A {@code MutableCallSite} is a {@link CallSite} whose target variable
- * behaves like an ordinary field.
- * An {@code invokedynamic} instruction linked to a {@code MutableCallSite} delegates
- * all calls to the site's current target.
- * The {@linkplain CallSite#dynamicInvoker dynamic invoker} of a mutable call site
- * also delegates each call to the site's current target.
- * <p>
- * Here is an example of a mutable call site which introduces a
- * state variable into a method handle chain.
- * <blockquote><pre>
-MutableCallSite name = new MutableCallSite(MethodType.methodType(String.class));
-MethodHandle MH_name = name.dynamicInvoker();
-MethodType MT_str2 = MethodType.methodType(String.class, String.class);
-MethodHandle MH_upcase = MethodHandles.lookup()
- .findVirtual(String.class, "toUpperCase", MT_str2);
-MethodHandle worker1 = MethodHandles.filterReturnValue(MH_name, MH_upcase);
-name.setTarget(MethodHandles.constant(String.class, "Rocky"));
-assertEquals("ROCKY", (String) worker1.invokeExact());
-name.setTarget(MethodHandles.constant(String.class, "Fred"));
-assertEquals("FRED", (String) worker1.invokeExact());
-// (mutation can be continued indefinitely)
- * </pre></blockquote>
- * <p>
- * The same call site may be used in several places at once.
- * <blockquote><pre>
-MethodHandle MH_dear = MethodHandles.lookup()
- .findVirtual(String.class, "concat", MT_str2).bindTo(", dear?");
-MethodHandle worker2 = MethodHandles.filterReturnValue(MH_name, MH_dear);
-assertEquals("Fred, dear?", (String) worker2.invokeExact());
-name.setTarget(MethodHandles.constant(String.class, "Wilma"));
-assertEquals("WILMA", (String) worker1.invokeExact());
-assertEquals("Wilma, dear?", (String) worker2.invokeExact());
- * </pre></blockquote>
- * <p>
- * <em>Non-synchronization of target values:</em>
- * A write to a mutable call site's target does not force other threads
- * to become aware of the updated value. Threads which do not perform
- * suitable synchronization actions relative to the updated call site
- * may cache the old target value and delay their use of the new target
- * value indefinitely.
- * (This is a normal consequence of the Java Memory Model as applied
- * to object fields.)
- * <p>
- * The {@link #syncAll syncAll} operation provides a way to force threads
- * to accept a new target value, even if there is no other synchronization.
- * <p>
- * For target values which will be frequently updated, consider using
- * a {@linkplain VolatileCallSite volatile call site} instead.
- * @author John Rose, JSR 292 EG
- */
-public class MutableCallSite extends CallSite {
- /**
- * Creates a blank call site object with the given method type.
- * The initial target is set to a method handle of the given type
- * which will throw an {@link IllegalStateException} if called.
- * <p>
- * The type of the call site is permanently set to the given type.
- * <p>
- * Before this {@code CallSite} object is returned from a bootstrap method,
- * or invoked in some other manner,
- * it is usually provided with a more useful target method,
- * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}.
- * @param type the method type that this call site will have
- * @throws NullPointerException if the proposed type is null
- */
- public MutableCallSite(MethodType type) {
- super(type);
- }
-
- /**
- * Creates a call site object with an initial target method handle.
- * The type of the call site is permanently set to the initial target's type.
- * @param target the method handle that will be the initial target of the call site
- * @throws NullPointerException if the proposed target is null
- */
- public MutableCallSite(MethodHandle target) {
- super(target);
- }
-
- /**
- * Returns the target method of the call site, which behaves
- * like a normal field of the {@code MutableCallSite}.
- * <p>
- * The interactions of {@code getTarget} with memory are the same
- * as of a read from an ordinary variable, such as an array element or a
- * non-volatile, non-final field.
- * <p>
- * In particular, the current thread may choose to reuse the result
- * of a previous read of the target from memory, and may fail to see
- * a recent update to the target by another thread.
- *
- * @return the linkage state of this call site, a method handle which can change over time
- * @see #setTarget
- */
- @Override public final MethodHandle getTarget() {
- return target;
- }
-
- /**
- * Updates the target method of this call site, as a normal variable.
- * The type of the new target must agree with the type of the old target.
- * <p>
- * The interactions with memory are the same
- * as of a write to an ordinary variable, such as an array element or a
- * non-volatile, non-final field.
- * <p>
- * In particular, unrelated threads may fail to see the updated target
- * until they perform a read from memory.
- * Stronger guarantees can be created by putting appropriate operations
- * into the bootstrap method and/or the target methods used
- * at any given call site.
- *
- * @param newTarget the new target
- * @throws NullPointerException if the proposed new target is null
- * @throws WrongMethodTypeException if the proposed new target
- * has a method type that differs from the previous target
- * @see #getTarget
- */
- @Override public void setTarget(MethodHandle newTarget) {
- checkTargetChange(this.target, newTarget);
- setTargetNormal(newTarget);
- }
-
- /**
- * {@inheritDoc}
- */
- @Override
- public final MethodHandle dynamicInvoker() {
- return makeDynamicInvoker();
- }
-
- /**
- * Performs a synchronization operation on each call site in the given array,
- * forcing all other threads to throw away any cached values previously
- * loaded from the target of any of the call sites.
- * <p>
- * This operation does not reverse any calls that have already started
- * on an old target value.
- * (Java supports {@linkplain java.lang.Object#wait() forward time travel} only.)
- * <p>
- * The overall effect is to force all future readers of each call site's target
- * to accept the most recently stored value.
- * ("Most recently" is reckoned relative to the {@code syncAll} itself.)
- * Conversely, the {@code syncAll} call may block until all readers have
- * (somehow) decached all previous versions of each call site's target.
- * <p>
- * To avoid race conditions, calls to {@code setTarget} and {@code syncAll}
- * should generally be performed under some sort of mutual exclusion.
- * Note that reader threads may observe an updated target as early
- * as the {@code setTarget} call that install the value
- * (and before the {@code syncAll} that confirms the value).
- * On the other hand, reader threads may observe previous versions of
- * the target until the {@code syncAll} call returns
- * (and after the {@code setTarget} that attempts to convey the updated version).
- * <p>
- * This operation is likely to be expensive and should be used sparingly.
- * If possible, it should be buffered for batch processing on sets of call sites.
- * <p>
- * If {@code sites} contains a null element,
- * a {@code NullPointerException} will be raised.
- * In this case, some non-null elements in the array may be
- * processed before the method returns abnormally.
- * Which elements these are (if any) is implementation-dependent.
- *
- * <h3>Java Memory Model details</h3>
- * In terms of the Java Memory Model, this operation performs a synchronization
- * action which is comparable in effect to the writing of a volatile variable
- * by the current thread, and an eventual volatile read by every other thread
- * that may access one of the affected call sites.
- * <p>
- * The following effects are apparent, for each individual call site {@code S}:
- * <ul>
- * <li>A new volatile variable {@code V} is created, and written by the current thread.
- * As defined by the JMM, this write is a global synchronization event.
- * <li>As is normal with thread-local ordering of write events,
- * every action already performed by the current thread is
- * taken to happen before the volatile write to {@code V}.
- * (In some implementations, this means that the current thread
- * performs a global release operation.)
- * <li>Specifically, the write to the current target of {@code S} is
- * taken to happen before the volatile write to {@code V}.
- * <li>The volatile write to {@code V} is placed
- * (in an implementation specific manner)
- * in the global synchronization order.
- * <li>Consider an arbitrary thread {@code T} (other than the current thread).
- * If {@code T} executes a synchronization action {@code A}
- * after the volatile write to {@code V} (in the global synchronization order),
- * it is therefore required to see either the current target
- * of {@code S}, or a later write to that target,
- * if it executes a read on the target of {@code S}.
- * (This constraint is called "synchronization-order consistency".)
- * <li>The JMM specifically allows optimizing compilers to elide
- * reads or writes of variables that are known to be useless.
- * Such elided reads and writes have no effect on the happens-before
- * relation. Regardless of this fact, the volatile {@code V}
- * will not be elided, even though its written value is
- * indeterminate and its read value is not used.
- * </ul>
- * Because of the last point, the implementation behaves as if a
- * volatile read of {@code V} were performed by {@code T}
- * immediately after its action {@code A}. In the local ordering
- * of actions in {@code T}, this read happens before any future
- * read of the target of {@code S}. It is as if the
- * implementation arbitrarily picked a read of {@code S}'s target
- * by {@code T}, and forced a read of {@code V} to precede it,
- * thereby ensuring communication of the new target value.
- * <p>
- * As long as the constraints of the Java Memory Model are obeyed,
- * implementations may delay the completion of a {@code syncAll}
- * operation while other threads ({@code T} above) continue to
- * use previous values of {@code S}'s target.
- * However, implementations are (as always) encouraged to avoid
- * livelock, and to eventually require all threads to take account
- * of the updated target.
- *
- * <p style="font-size:smaller;">
- * <em>Discussion:</em>
- * For performance reasons, {@code syncAll} is not a virtual method
- * on a single call site, but rather applies to a set of call sites.
- * Some implementations may incur a large fixed overhead cost
- * for processing one or more synchronization operations,
- * but a small incremental cost for each additional call site.
- * In any case, this operation is likely to be costly, since
- * other threads may have to be somehow interrupted
- * in order to make them notice the updated target value.
- * However, it may be observed that a single call to synchronize
- * several sites has the same formal effect as many calls,
- * each on just one of the sites.
- *
- * <p style="font-size:smaller;">
- * <em>Implementation Note:</em>
- * Simple implementations of {@code MutableCallSite} may use
- * a volatile variable for the target of a mutable call site.
- * In such an implementation, the {@code syncAll} method can be a no-op,
- * and yet it will conform to the JMM behavior documented above.
- *
- * @param sites an array of call sites to be synchronized
- * @throws NullPointerException if the {@code sites} array reference is null
- * or the array contains a null
- */
- public static void syncAll(MutableCallSite[] sites) {
- if (sites.length == 0) return;
- STORE_BARRIER.lazySet(0);
- for (int i = 0; i < sites.length; i++) {
- sites[i].getClass(); // trigger NPE on first null
- }
- // FIXME: NYI
- }
- private static final AtomicInteger STORE_BARRIER = new AtomicInteger();
-}