265 lines
11 KiB
Java
265 lines
11 KiB
Java
/*
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* Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* Extensively modified for IKVM.NET by Jeroen Frijters
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* Copyright (C) 2011 Jeroen Frijters
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*/
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package java.lang.invoke;
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import sun.invoke.empty.Empty;
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import sun.misc.Unsafe;
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import static java.lang.invoke.MethodHandleStatics.*;
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import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
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/**
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* A {@code CallSite} is a holder for a variable {@link MethodHandle},
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* which is called its {@code target}.
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* An {@code invokedynamic} instruction linked to a {@code CallSite} delegates
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* all calls to the site's current target.
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* A {@code CallSite} may be associated with several {@code invokedynamic}
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* instructions, or it may be "free floating", associated with none.
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* In any case, it may be invoked through an associated method handle
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* called its {@linkplain #dynamicInvoker dynamic invoker}.
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* <p>
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* {@code CallSite} is an abstract class which does not allow
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* direct subclassing by users. It has three immediate,
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* concrete subclasses that may be either instantiated or subclassed.
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* <ul>
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* <li>If a mutable target is not required, an {@code invokedynamic} instruction
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* may be permanently bound by means of a {@linkplain ConstantCallSite constant call site}.
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* <li>If a mutable target is required which has volatile variable semantics,
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* because updates to the target must be immediately and reliably witnessed by other threads,
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* a {@linkplain VolatileCallSite volatile call site} may be used.
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* <li>Otherwise, if a mutable target is required,
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* a {@linkplain MutableCallSite mutable call site} may be used.
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* </ul>
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* <p>
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* A non-constant call site may be <em>relinked</em> by changing its target.
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* The new target must have the same {@linkplain MethodHandle#type() type}
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* as the previous target.
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* Thus, though a call site can be relinked to a series of
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* successive targets, it cannot change its type.
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* <p>
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* Here is a sample use of call sites and bootstrap methods which links every
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* dynamic call site to print its arguments:
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<blockquote><pre><!-- see indy-demo/src/PrintArgsDemo.java -->
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static void test() throws Throwable {
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// THE FOLLOWING LINE IS PSEUDOCODE FOR A JVM INSTRUCTION
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InvokeDynamic[#bootstrapDynamic].baz("baz arg", 2, 3.14);
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}
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private static void printArgs(Object... args) {
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System.out.println(java.util.Arrays.deepToString(args));
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}
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private static final MethodHandle printArgs;
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static {
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MethodHandles.Lookup lookup = MethodHandles.lookup();
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Class thisClass = lookup.lookupClass(); // (who am I?)
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printArgs = lookup.findStatic(thisClass,
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"printArgs", MethodType.methodType(void.class, Object[].class));
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}
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private static CallSite bootstrapDynamic(MethodHandles.Lookup caller, String name, MethodType type) {
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// ignore caller and name, but match the type:
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return new ConstantCallSite(printArgs.asType(type));
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}
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</pre></blockquote>
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* @author John Rose, JSR 292 EG
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*/
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abstract
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public class CallSite {
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interface IndyCallSite {
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void setTarget(Object target);
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}
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// The actual payload of this call site:
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/*package-private*/
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volatile MethodHandle target;
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final IndyCallSite ics;
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/**
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* Make a blank call site object with the given method type.
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* An initial target method is supplied which will throw
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* an {@link IllegalStateException} if called.
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* <p>
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* Before this {@code CallSite} object is returned from a bootstrap method,
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* it is usually provided with a more useful target method,
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* via a call to {@link CallSite#setTarget(MethodHandle) setTarget}.
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* @throws NullPointerException if the proposed type is null
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*/
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/*package-private*/
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CallSite(MethodType type) {
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this(type.invokers().uninitializedCallSite());
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}
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/**
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* Make a call site object equipped with an initial target method handle.
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* @param target the method handle which will be the initial target of the call site
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* @throws NullPointerException if the proposed target is null
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*/
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/*package-private*/
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CallSite(MethodHandle target) {
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target.getClass(); // null check
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ics = createIndyCallSite(target.vmtarget);
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setTargetNormal(target);
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}
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private static native IndyCallSite createIndyCallSite(Object target);
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final void setTargetNormal(MethodHandle target) {
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this.target = target;
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ics.setTarget(target.vmtarget);
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}
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final void setTargetVolatile(MethodHandle target) {
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synchronized(ics) {
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setTargetNormal(target);
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}
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}
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final MethodHandle getTargetVolatile() {
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synchronized(ics) {
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return target;
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}
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}
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/**
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* Make a call site object equipped with an initial target method handle.
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* @param targetType the desired type of the call site
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* @param createTargetHook a hook which will bind the call site to the target method handle
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* @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments,
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* or if the target returned by the hook is not of the given {@code targetType}
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* @throws NullPointerException if the hook returns a null value
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* @throws ClassCastException if the hook returns something other than a {@code MethodHandle}
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* @throws Throwable anything else thrown by the the hook function
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*/
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/*package-private*/
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CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {
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this(targetType);
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ConstantCallSite selfCCS = (ConstantCallSite) this;
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MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS);
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checkTargetChange(this.target, boundTarget);
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setTargetNormal(boundTarget);
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}
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/**
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* Returns the type of this call site's target.
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* Although targets may change, any call site's type is permanent, and can never change to an unequal type.
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* The {@code setTarget} method enforces this invariant by refusing any new target that does
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* not have the previous target's type.
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* @return the type of the current target, which is also the type of any future target
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*/
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public MethodType type() {
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// warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException
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return target.type();
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}
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/**
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* Returns the target method of the call site, according to the
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* behavior defined by this call site's specific class.
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* The immediate subclasses of {@code CallSite} document the
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* class-specific behaviors of this method.
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*
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* @return the current linkage state of the call site, its target method handle
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* @see ConstantCallSite
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* @see VolatileCallSite
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* @see #setTarget
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* @see ConstantCallSite#getTarget
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* @see MutableCallSite#getTarget
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* @see VolatileCallSite#getTarget
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*/
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public abstract MethodHandle getTarget();
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/**
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* Updates the target method of this call site, according to the
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* behavior defined by this call site's specific class.
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* The immediate subclasses of {@code CallSite} document the
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* class-specific behaviors of this method.
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* <p>
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* The type of the new target must be {@linkplain MethodType#equals equal to}
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* the type of the old target.
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*
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* @param newTarget the new target
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* @throws NullPointerException if the proposed new target is null
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* @throws WrongMethodTypeException if the proposed new target
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* has a method type that differs from the previous target
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* @see CallSite#getTarget
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* @see ConstantCallSite#setTarget
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* @see MutableCallSite#setTarget
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* @see VolatileCallSite#setTarget
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*/
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public abstract void setTarget(MethodHandle newTarget);
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void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) {
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MethodType oldType = oldTarget.type();
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MethodType newType = newTarget.type(); // null check!
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if (!newType.equals(oldType))
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throw wrongTargetType(newTarget, oldType);
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}
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private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {
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return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type);
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}
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/**
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* Produces a method handle equivalent to an invokedynamic instruction
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* which has been linked to this call site.
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* <p>
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* This method is equivalent to the following code:
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* <blockquote><pre>
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* MethodHandle getTarget, invoker, result;
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* getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class));
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* invoker = MethodHandles.exactInvoker(this.type());
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* result = MethodHandles.foldArguments(invoker, getTarget)
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* </pre></blockquote>
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*
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* @return a method handle which always invokes this call site's current target
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*/
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public abstract MethodHandle dynamicInvoker();
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/*non-public*/ MethodHandle makeDynamicInvoker() {
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MethodHandle getTarget = MethodHandleImpl.bindReceiver(GET_TARGET, this);
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MethodHandle invoker = MethodHandles.exactInvoker(this.type());
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return MethodHandles.foldArguments(invoker, getTarget);
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}
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private static final MethodHandle GET_TARGET;
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static {
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try {
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GET_TARGET = IMPL_LOOKUP.
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findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class));
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} catch (ReflectiveOperationException ignore) {
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throw new InternalError();
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}
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}
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/** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
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/*package-private*/
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static Empty uninitializedCallSite() {
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throw new IllegalStateException("uninitialized call site");
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}
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}
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