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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
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   *
   * 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).
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   * You should have received a copy of the GNU General Public License version
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   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  package java.lang.invoke;
  
  // Android-changed: removed references to MutableCallSite.syncAll().
  /**
   * 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.
   * <!-- JavaDocExamplesTest.testMutableCallSite -->
   * <blockquote><pre>{@code
  MutableCallSite name = new MutableCallSite(MethodType.methodType(String.class));
  MethodHandle MH_name = name.dynamicInvoker();
  MethodType MT_str1 = MethodType.methodType(String.class);
  MethodHandle MH_upcase = MethodHandles.lookup()
      .findVirtual(String.class, "toUpperCase", MT_str1);
  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>{@code
  MethodType MT_str2 = MethodType.methodType(String.class, String.class);
  MethodHandle MH_cat = lookup().findVirtual(String.class,
    "concat", methodType(String.class, String.class));
  MethodHandle MH_dear = MethodHandles.insertArguments(MH_cat, 1, ", 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>
   * 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();
      }
  
      // BEGIN Android-removed: syncAll() implementation is incomplete.
      /**
       * 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 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.
       *
       * <h1>Java Memory Model details</h1>
       * 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();
      */
      // END Android-removed: syncAll() implementation is incomplete.
  }
  