/*
* Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*/
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 =
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);
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.
bindArgumentL(0, this);
MethodHandle invoker =
MethodHandles.
exactInvoker(this.
type());
return
MethodHandles.
foldArguments(
invoker,
getTarget);
}
private static final
MethodHandle GET_TARGET;
private static final
MethodHandle THROW_UCS;
static {
try {
GET_TARGET =
IMPL_LOOKUP.
findVirtual(
CallSite.class, "getTarget",
MethodType.
methodType(
MethodHandle.class));
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 =
THROW_UCS.
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 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) {
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
wrongTargetType(
site.
getTarget(),
type);
} 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]);
}
}
}