content: /*
   * Copyright (c) 2008, 2013, 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.lang.invoke;
  
  // Android-changed: Not using Empty
  //import sun.invoke.empty.Empty;
  import static java.lang.invoke.MethodHandleStatics.*;
  import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
  
  /**
   * A {@code CallSite} is a holder for a variable {@link MethodHandle},
   * which is called its {@code target}.
   * An {@code invokedynamic} instruction linked to a {@code CallSite} delegates
   * all calls to the site's current target.
   * A {@code CallSite} may be associated with several {@code invokedynamic}
   * instructions, or it may be "free floating", associated with none.
   * In any case, it may be invoked through an associated method handle
   * called its {@linkplain #dynamicInvoker dynamic invoker}.
   * <p>
   * {@code CallSite} is an abstract class which does not allow
   * direct subclassing by users.  It has three immediate,
   * concrete subclasses that may be either instantiated or subclassed.
   * <ul>
   * <li>If a mutable target is not required, an {@code invokedynamic} instruction
   * may be permanently bound by means of a {@linkplain ConstantCallSite constant call site}.
   * <li>If a mutable target is required which has volatile variable semantics,
   * because updates to the target must be immediately and reliably witnessed by other threads,
   * a {@linkplain VolatileCallSite volatile call site} may be used.
   * <li>Otherwise, if a mutable target is required,
   * a {@linkplain MutableCallSite mutable call site} may be used.
   * </ul>
   * <p>
   * A non-constant call site may be <em>relinked</em> by changing its target.
   * The new target must have the same {@linkplain MethodHandle#type() type}
   * as the previous target.
   * Thus, though a call site can be relinked to a series of
   * successive targets, it cannot change its type.
   * <p>
   * Here is a sample use of call sites and bootstrap methods which links every
   * dynamic call site to print its arguments:
  <blockquote><pre>{@code
  static void test() throws Throwable {
      // THE FOLLOWING LINE IS PSEUDOCODE FOR A JVM INSTRUCTION
      InvokeDynamic[#bootstrapDynamic].baz("baz arg", 2, 3.14);
  }
  private static void printArgs(Object... args) {
    System.out.println(java.util.Arrays.deepToString(args));
  }
  private static final MethodHandle printArgs;
  static {
    MethodHandles.Lookup lookup = MethodHandles.lookup();
    Class thisClass = lookup.lookupClass();  // (who am I?)
    printArgs = lookup.findStatic(thisClass,
        "printArgs", MethodType.methodType(void.class, Object[].class));
  }
  private static CallSite bootstrapDynamic(MethodHandles.Lookup caller, String name, MethodType type) {
    // ignore caller and name, but match the type:
    return new ConstantCallSite(printArgs.asType(type));
  }
  }</pre></blockquote>
   * @author John Rose, JSR 292 EG
   */
  abstract
  public class CallSite {
      // Android-changed: not used.
      // static { MethodHandleImpl.initStatics(); }
  
      // The actual payload of this call site:
      /*package-private*/
      MethodHandle target;    // Note: This field is known to the JVM.  Do not change.
  
      /**
       * Make a blank call site object with the given method type.
       * An initial target method is supplied which will throw
       * an {@link IllegalStateException} if called.
       * <p>
       * Before this {@code CallSite} object is returned from a bootstrap method,
       * it is usually provided with a more useful target method,
       * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}.
       * @throws NullPointerException if the proposed type is null
       */
      /*package-private*/
      CallSite(MethodType type) {
          // Android-changed: No cache for these so create uninitializedCallSite target here using
          // method handle transformations to create a method handle that has the expected method
          // type but throws an IllegalStateException.
          // target = makeUninitializedCallSite(type);
          this.target = MethodHandles.throwException(type.returnType(), IllegalStateException.class);
          this.target = MethodHandles.insertArguments(
              this.target, 0, new IllegalStateException("uninitialized call site"));
          if (type.parameterCount() > 0) {
              this.target = MethodHandles.dropArguments(this.target, 0, type.ptypes());
          }
  
          // Android-changed: Using initializer method for GET_TARGET
          // rather than complex static initializer.
          initializeGetTarget();
      }
  
      /**
       * Make a call site object equipped with an initial target method handle.
       * @param target the method handle which will be the initial target of the call site
       * @throws NullPointerException if the proposed target is null
       */
      /*package-private*/
      CallSite(MethodHandle target) {
          target.type();  // null check
          this.target = target;
  
          // Android-changed: Using initializer method for GET_TARGET
          // rather than complex static initializer.
          initializeGetTarget();
      }
  
      /**
       * Make a call site object equipped with an initial target method handle.
       * @param targetType the desired type of the call site
       * @param createTargetHook a hook which will bind the call site to the target method handle
       * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments,
       *         or if the target returned by the hook is not of the given {@code targetType}
       * @throws NullPointerException if the hook returns a null value
       * @throws ClassCastException if the hook returns something other than a {@code MethodHandle}
       * @throws Throwable anything else thrown by the hook function
       */
      /*package-private*/
      CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {
          this(targetType);
          ConstantCallSite selfCCS = (ConstantCallSite) this;
          MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS);
          checkTargetChange(this.target, boundTarget);
          this.target = boundTarget;
  
          // Android-changed: Using initializer method for GET_TARGET
          // rather than complex static initializer.
          initializeGetTarget();
      }
  
      /**
       * Returns the type of this call site's target.
       * Although targets may change, any call site's type is permanent, and can never change to an unequal type.
       * The {@code setTarget} method enforces this invariant by refusing any new target that does
       * not have the previous target's type.
       * @return the type of the current target, which is also the type of any future target
       */
      public MethodType type() {
          // warning:  do not call getTarget here, because CCS.getTarget can throw IllegalStateException
          return target.type();
      }
  
      /**
       * Returns the target method of the call site, according to the
       * behavior defined by this call site's specific class.
       * The immediate subclasses of {@code CallSite} document the
       * class-specific behaviors of this method.
       *
       * @return the current linkage state of the call site, its target method handle
       * @see ConstantCallSite
       * @see VolatileCallSite
       * @see #setTarget
       * @see ConstantCallSite#getTarget
       * @see MutableCallSite#getTarget
       * @see VolatileCallSite#getTarget
       */
      public abstract MethodHandle getTarget();
  
      /**
       * Updates the target method of this call site, according to the
       * behavior defined by this call site's specific class.
       * The immediate subclasses of {@code CallSite} document the
       * class-specific behaviors of this method.
       * <p>
       * The type of the new target must be {@linkplain MethodType#equals equal to}
       * the type of the old target.
       *
       * @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 CallSite#getTarget
       * @see ConstantCallSite#setTarget
       * @see MutableCallSite#setTarget
       * @see VolatileCallSite#setTarget
       */
      public abstract void setTarget(MethodHandle newTarget);
  
      void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) {
          MethodType oldType = oldTarget.type();
          MethodType newType = newTarget.type();  // null check!
          if (!newType.equals(oldType))
              throw wrongTargetType(newTarget, oldType);
      }
  
      private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {
          return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type);
      }
  
      /**
       * Produces a method handle equivalent to an invokedynamic instruction
       * which has been linked to this call site.
       * <p>
       * This method is equivalent to the following code:
       * <blockquote><pre>{@code
       * MethodHandle getTarget, invoker, result;
       * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class));
       * invoker = MethodHandles.exactInvoker(this.type());
       * result = MethodHandles.foldArguments(invoker, getTarget)
       * }</pre></blockquote>
       *
       * @return a method handle which always invokes this call site's current target
       */
      public abstract MethodHandle dynamicInvoker();
  
      /*non-public*/ MethodHandle makeDynamicInvoker() {
          // Android-changed: Use bindTo() rather than bindArgumentL() (not implemented).
          MethodHandle getTarget = GET_TARGET.bindTo(this);
          MethodHandle invoker = MethodHandles.exactInvoker(this.type());
          return MethodHandles.foldArguments(invoker, getTarget);
      }
  
      // Android-changed: no longer final. GET_TARGET assigned in initializeGetTarget().
      private static MethodHandle GET_TARGET = null;
  
      private void initializeGetTarget() {
          // Android-changed: moved from static initializer for
          // GET_TARGET to avoid issues with running early. Called from
          // constructors. CallSite creation is not performance critical.
          synchronized (CallSite.class) {
              if (GET_TARGET == null) {
                  try {
                      GET_TARGET = IMPL_LOOKUP.
                              findVirtual(CallSite.class, "getTarget",
                                          MethodType.methodType(MethodHandle.class));
                  } catch (ReflectiveOperationException e) {
                      throw new InternalError(e);
                  }
              }
          }
      }
  
      // Android-changed: not used.
      // /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
      // /*package-private*/
      // static Empty uninitializedCallSite() {
      //     throw new IllegalStateException("uninitialized call site");
      // }
  
      // unsafe stuff:
      private static final long TARGET_OFFSET;
      static {
          try {
              TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class.getDeclaredField("target"));
          } catch (Exception ex) { throw new Error(ex); }
      }
  
      /*package-private*/
      void setTargetNormal(MethodHandle newTarget) {
          // Android-changed: Set value directly.
          // MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);
          target = newTarget;
      }
      /*package-private*/
      MethodHandle getTargetVolatile() {
          return (MethodHandle) UNSAFE.getObjectVolatile(this, TARGET_OFFSET);
      }
      /*package-private*/
      void setTargetVolatile(MethodHandle newTarget) {
          // Android-changed: Set value directly.
          // MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);
          UNSAFE.putObjectVolatile(this, TARGET_OFFSET, newTarget);
      }
  
      // Android-changed: not used.
      // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite:
      // static CallSite makeSite(MethodHandle bootstrapMethod,
      //                          // Callee information:
      //                          String name, MethodType type,
      //                          // Extra arguments for BSM, if any:
      //                          Object info,
      //                          // Caller information:
      //                          Class<?> callerClass) {
      //     MethodHandles.Lookup caller = IMPL_LOOKUP.in(callerClass);
      //     CallSite site;
      //     try {
      //         Object binding;
      //         info = maybeReBox(info);
      //         if (info == null) {
      //             binding = bootstrapMethod.invoke(caller, name, type);
      //         } else if (!info.getClass().isArray()) {
      //             binding = bootstrapMethod.invoke(caller, name, type, info);
      //         } else {
      //             Object[] argv = (Object[]) info;
      //             maybeReBoxElements(argv);
      //             switch (argv.length) {
      //             case 0:
      //                 binding = bootstrapMethod.invoke(caller, name, type);
      //                 break;
      //             case 1:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0]);
      //                 break;
      //             case 2:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0], argv[1]);
      //                 break;
      //             case 3:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0], argv[1], argv[2]);
      //                 break;
      //             case 4:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0], argv[1], argv[2], argv[3]);
      //                 break;
      //             case 5:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0], argv[1], argv[2], argv[3], argv[4]);
      //                 break;
      //             case 6:
      //                 binding = bootstrapMethod.invoke(caller, name, type,
      //                                                  argv[0], argv[1], argv[2], argv[3], argv[4], argv[5]);
      //                 break;
      //             default:
      //                 final int NON_SPREAD_ARG_COUNT = 3;  // (caller, name, type)
      //                 if (NON_SPREAD_ARG_COUNT + argv.length > MethodType.MAX_MH_ARITY)
      //                     throw new BootstrapMethodError("too many bootstrap method arguments");
      //                 MethodType bsmType = bootstrapMethod.type();
      //                 MethodType invocationType = MethodType.genericMethodType(NON_SPREAD_ARG_COUNT + argv.length);
      //                 MethodHandle typedBSM = bootstrapMethod.asType(invocationType);
      //                 MethodHandle spreader = invocationType.invokers().spreadInvoker(NON_SPREAD_ARG_COUNT);
      //                 binding = spreader.invokeExact(typedBSM, (Object)caller, (Object)name, (Object)type, argv);
      //             }
      //         }
      //         //System.out.println("BSM for "+name+type+" => "+binding);
      //         if (binding instanceof CallSite) {
      //             site = (CallSite) binding;
      //         }  else {
      //             throw new ClassCastException("bootstrap method failed to produce a CallSite");
      //         }
      //         if (!site.getTarget().type().equals(type))
      //             throw wrongTargetType(site.getTarget(), type);
      //     } catch (Throwable ex) {
      //         BootstrapMethodError bex;
      //         if (ex instanceof BootstrapMethodError)
      //             bex = (BootstrapMethodError) ex;
      //         else
      //             bex = new BootstrapMethodError("call site initialization exception", ex);
      //         throw bex;
      //     }
      //     return site;
      // }
  
      // private static Object maybeReBox(Object x) {
      //     if (x instanceof Integer) {
      //         int xi = (int) x;
      //         if (xi == (byte) xi)
      //             x = xi;  // must rebox; see JLS 5.1.7
      //     }
      //     return x;
      // }
      // private static void maybeReBoxElements(Object[] xa) {
      //     for (int i = 0; i < xa.length; i++) {
      //         xa[i] = maybeReBox(xa[i]);
      //     }
      // }
  }
  