/* * 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 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}. *

* {@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. *

*

* A non-constant call site may be relinked 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. *

* Here is a sample use of call sites and bootstrap methods which links every * dynamic call site to print its arguments:


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));
}
* @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. *

* 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(); } /** * 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. *

* 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. *

* This method is equivalent to the following 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)
     * 
* * @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"); } // 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) { MethodHandleNatives.setCallSiteTargetNormal(this, newTarget); } /*package-private*/ MethodHandle getTargetVolatile() { return (MethodHandle) UNSAFE.getObjectVolatile(this, TARGET_OFFSET); } /*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) { 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]); } } }