/*

  * 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;

 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 {

     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) {

         target = type.invokers().uninitializedCallSite();

     }

     /**

      * 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;

     }

     /**

      * 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;

     }

     /**

      * 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() {

         MethodHandle getTarget = GET_TARGET.bindReceiver(this);

         MethodHandle invoker = MethodHandles.exactInvoker(this.type());

         return MethodHandles.foldArguments(invoker, getTarget);

     }

     private static final MethodHandle GET_TARGET;

     static {

         try {

             GET_TARGET = IMPL_LOOKUP.

                 findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class));

         } catch (ReflectiveOperationException e) {

             throw newInternalError(e);

         }

     }

     /** 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");

     }

     /*package-private*/

     void setTargetNormal(MethodHandle newTarget) {

         MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);

     }

     /*package-private*/

     MethodHandle getTargetVolatile() {

         return target;

     }

     /*package-private*/

     void setTargetVolatile(MethodHandle newTarget) {

         MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);

     }

     // 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 new WrongMethodTypeException("wrong type: "+site.getTarget());

         } 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]);

         }

     }

 }