/* * 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.lang.invoke; import sun.invoke.empty.Empty;import sun.misc.Unsafe;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><!-- see indy-demo/src/PrintArgsDemo.java -->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 */abstractpublic class CallSite {    static { MethodHandleImpl.initStatics(); }     // Fields used only by the JVM.  Do not use or change.    private MemberName vmmethod; // supplied by the JVM (ref. to calling method)    private int        vmindex;  // supplied by the JVM (BCI within calling method)     // The actual payload of this call site:    /*package-private*/    MethodHandle target;     /**     * 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 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();    }     /** Called from JVM (or low-level Java code) after the BSM returns the newly created CallSite.     *  The parameters are JVM-specific.     */    void initializeFromJVM(String name,                           MethodType type,                           MemberName callerMethod,                           int        callerBCI) {        if (this.vmmethod != null) {            // FIXME            throw new BootstrapMethodError("call site has already been linked to an invokedynamic instruction");        }        if (!this.type().equals(type)) {            throw wrongTargetType(target, type);        }        this.vmindex  = callerBCI;        this.vmmethod = callerMethod;    }     /**     * 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>     * 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 = MethodHandleImpl.bindReceiver(GET_TARGET, 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 ignore) {            throw new InternalError();        }    }     /** 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 Unsafe unsafe = Unsafe.getUnsafe();    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) {        target = newTarget;    }    /*package-private*/    MethodHandle getTargetVolatile() {        return (MethodHandle) unsafe.getObjectVolatile(this, TARGET_OFFSET);    }    /*package-private*/    void setTargetVolatile(MethodHandle newTarget) {        unsafe.putObjectVolatile(this, TARGET_OFFSET, 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:                             MemberName callerMethod, int callerBCI) {        Class<?> callerClass = callerMethod.getDeclaringClass();        Object 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);                if (3 + argv.length > 255)                    throw new BootstrapMethodError("too many bootstrap method arguments");                MethodType bsmType = bootstrapMethod.type();                if (bsmType.parameterCount() == 4 && bsmType.parameterType(3) == Object[].class)                    binding = bootstrapMethod.invoke(caller, name, type, argv);                else                    binding = MethodHandles.spreadInvoker(bsmType, 3)                        .invoke(bootstrapMethod, caller, name, 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]);        }    }}