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/*
* Copyright (c) 2008, 2016, 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 static java.lang.invoke.MethodHandleStatics.*;
import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
import jdk.internal.vm.annotation.Stable;
/**
* 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
* @since 1.7
*/
abstract
public class CallSite {
// The actual payload of this call site.
// Can be modified using {@link MethodHandleNatives#setCallSiteTargetNormal} or {@link MethodHandleNatives#setCallSiteTargetVolatile}.
/*package-private*/
final MethodHandle target; // Note: This field is known to the JVM.
/**
* 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 = makeUninitializedCallSite(type);
}
/**
* 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); // need to initialize target to make CallSite.type() work in createTargetHook
ConstantCallSite selfCCS = (ConstantCallSite) this;
MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS);
setTargetNormal(boundTarget); // ConstantCallSite doesn't publish CallSite.target
UNSAFE.storeStoreFence(); // barrier between target and isFrozen updates
}
/**
* {@code CallSite} dependency context.
* JVM uses CallSite.context to store nmethod dependencies on the call site target.
*/
private final MethodHandleNatives.CallSiteContext context = MethodHandleNatives.CallSiteContext.make(this);
/**
* 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);
private void checkTargetChange(MethodHandle newTarget) {
MethodType oldType = target.type(); // target is always present
MethodType newType = newTarget.type(); // null check!
if (newType != 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();
/*package-private*/
MethodHandle makeDynamicInvoker() {
MethodHandle getTarget = getTargetHandle().bindArgumentL(0, this);
MethodHandle invoker = MethodHandles.exactInvoker(this.type());
return MethodHandles.foldArguments(invoker, getTarget);
}
private static @Stable MethodHandle GET_TARGET;
private static MethodHandle getTargetHandle() {
MethodHandle handle = GET_TARGET;
if (handle != null) {
return handle;
}
try {
return GET_TARGET = IMPL_LOOKUP.
findVirtual(CallSite.class, "getTarget",
MethodType.methodType(MethodHandle.class));
} catch (ReflectiveOperationException e) {
throw newInternalError(e);
}
}
private static @Stable MethodHandle THROW_UCS;
private static MethodHandle uninitializedCallSiteHandle() {
MethodHandle handle = THROW_UCS;
if (handle != null) {
return handle;
}
try {
return THROW_UCS = IMPL_LOOKUP.
findStatic(CallSite.class, "uninitializedCallSite",
MethodType.methodType(Object.class, Object[].class));
} catch (ReflectiveOperationException e) {
throw newInternalError(e);
}
}
/** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
private static Object uninitializedCallSite(Object... ignore) {
throw new IllegalStateException("uninitialized call site");
}
private MethodHandle makeUninitializedCallSite(MethodType targetType) {
MethodType basicType = targetType.basicType();
MethodHandle invoker = basicType.form().cachedMethodHandle(MethodTypeForm.MH_UNINIT_CS);
if (invoker == null) {
invoker = uninitializedCallSiteHandle().asType(basicType);
invoker = basicType.form().setCachedMethodHandle(MethodTypeForm.MH_UNINIT_CS, invoker);
}
// unchecked view is OK since no values will be received or returned
return invoker.viewAsType(targetType, false);
}
// unsafe stuff:
private static @Stable long TARGET_OFFSET;
private static long getTargetOffset() {
long offset = TARGET_OFFSET;
if (offset > 0) {
return offset;
}
offset = TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class, "target");
assert(offset > 0);
return offset;
}
/*package-private*/
final void setTargetNormal(MethodHandle newTarget) {
checkTargetChange(newTarget);
MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);
}
/*package-private*/
final MethodHandle getTargetVolatile() {
return (MethodHandle) UNSAFE.getReferenceVolatile(this, getTargetOffset());
}
/*package-private*/
final void setTargetVolatile(MethodHandle newTarget) {
checkTargetChange(newTarget);
MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);
}
// this implements the upcall from the JVM, MethodHandleNatives.linkCallSite:
/*package-private*/
static CallSite makeSite(MethodHandle bootstrapMethod,
// Callee information:
String name, MethodType type,
// Extra arguments for BSM, if any:
Object info,
// Caller information:
Class<?> callerClass) {
CallSite site;
try {
Object binding = BootstrapMethodInvoker.invoke(
CallSite.class, bootstrapMethod, name, type, info, callerClass);
if (binding instanceof CallSite) {
site = (CallSite) binding;
} else {
// See the "Linking Exceptions" section for the invokedynamic
// instruction in JVMS 6.5.
// Throws a runtime exception defining the cause that is then
// in the "catch (Throwable ex)" a few lines below wrapped in
// BootstrapMethodError
throw new ClassCastException("CallSite bootstrap method failed to produce an instance of CallSite");
}
if (!site.getTarget().type().equals(type)) {
// See the "Linking Exceptions" section for the invokedynamic
// instruction in JVMS 6.5.
// Throws a runtime exception defining the cause that is then
// in the "catch (Throwable ex)" a few lines below wrapped in
// BootstrapMethodError
throw wrongTargetType(site.getTarget(), type);
}
} catch (Error e) {
// Pass through an Error, including BootstrapMethodError, any other
// form of linkage error, such as IllegalAccessError if the bootstrap
// method is inaccessible, or say ThreadDeath/OutOfMemoryError
// See the "Linking Exceptions" section for the invokedynamic
// instruction in JVMS 6.5.
throw e;
} catch (Throwable ex) {
// Wrap anything else in BootstrapMethodError
throw new BootstrapMethodError("CallSite bootstrap method initialization exception", ex);
}
return site;
}
}