/*
* Copyright (c) 2008, 2010, 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.dyn;
import sun.dyn.Access;
import sun.dyn.MemberName;
import sun.dyn.CallSiteImpl;
/**
* A {@code CallSite} reifies an {@code invokedynamic} instruction from bytecode,
* and controls its linkage.
* Every linked {@code CallSite} object corresponds to a distinct instance
* of the {@code invokedynamic} instruction, and vice versa.
* <p>
* Every linked {@code CallSite} object has one state variable,
* a {@link MethodHandle} reference called the {@code target}.
* This reference is never null. Though it can change its value
* successive values must always have exactly the {@link MethodType method type}
* called for by the bytecodes of the associated {@code invokedynamic} instruction
* <p>
* It is the responsibility of each class's
* {@link Linkage#registerBootstrapMethod(Class, MethodHandle) bootstrap method}
* to produce call sites which have been pre-linked to an initial target method.
* The required {@link MethodType type} for the target method is a parameter
* to each bootstrap method call.
* <p>
* The bootstrap method may elect to produce call sites of a
* language-specific subclass of {@code CallSite}. In such a case,
* the subclass may claim responsibility for initializing its target to
* a non-null value, by overriding {@link #initialTarget}.
* <p>
* An {@code invokedynamic} instruction which has not yet been executed
* is said to be <em>unlinked</em>. When an unlinked call site is executed,
* the containing class's bootstrap method is called to manufacture a call site,
* for the instruction. If the bootstrap method does not assign a non-null
* value to the new call site's target variable, the method {@link #initialTarget}
* is called to produce the new call site's first target method.
* <p>
* A freshly-created {@code CallSite} object is not yet in a linked state.
* An unlinked {@code CallSite} object reports null for its {@code callerClass}.
* When the JVM receives a {@code CallSite} object from a bootstrap method,
* it first ensures that its target is non-null and of the correct type.
* The JVM then links the {@code CallSite} object to the call site instruction,
* enabling the {@code callerClass} to return the class in which the instruction occurs.
* <p>
* Next, the JVM links the instruction to the {@code CallSite}, at which point
* any further execution of the {@code invokedynamic} instruction implicitly
* invokes the current target of the {@code CallSite} object.
* After this two-way linkage, both the instruction and the {@code CallSite}
* object are said to be linked.
* <p>
* This state of linkage continues until the method containing the
* dynamic call site is garbage collected, or the dynamic call site
* is invalidated by an explicit request.
* <p>
* Linkage happens once in the lifetime of any given {@code CallSite} object.
* Because of call site invalidation, this linkage can be repeated for
* a single {@code invokedynamic} instruction, with multiple {@code CallSite} objects.
* When a {@code CallSite} is unlinked from an {@code invokedynamic} instruction,
* the instruction is reset so that it is no longer associated with
* the {@code CallSite} object, but the {@code CallSite} does not change
* state.
* <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 -->
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));
Linkage.registerBootstrapMethod("bootstrapDynamic");
}
private static CallSite bootstrapDynamic(Class caller, String name, MethodType type) {
// ignore caller and name, but match the type:
return new CallSite(MethodHandles.collectArguments(printArgs, type));
}
</pre></blockquote>
* @see Linkage#registerBootstrapMethod(java.lang.Class, java.dyn.MethodHandle)
* @author John Rose, JSR 292 EG
*/
public class CallSite
{
private static final Access IMPL_TOKEN = Access.getToken();
// 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:
private MethodHandle target;
// Remove this field for PFD and delete deprecated methods:
private MemberName calleeNameRemoveForPFD;
/**
* Make a blank call site object.
* Before it is returned from a bootstrap method, this {@code CallSite} object
* must be provided with
* a target method via a call to {@link CallSite#setTarget(MethodHandle) setTarget},
* or by a subclass override of {@link CallSite#initialTarget(Class,String,MethodType) initialTarget}.
*/
public CallSite() {
}
/**
* Make a blank call site object, possibly equipped with an initial target method handle.
* The initial target reference may be null, in which case the {@code CallSite} object
* must be provided with a target method via a call to {@link CallSite#setTarget},
* or by a subclass override of {@link CallSite#initialTarget}.
* @param target the method handle which will be the initial target of the call site, or null if there is none yet
*/
public CallSite(MethodHandle target) {
this.target = target;
}
/** @deprecated transitional form defined in EDR but removed in PFD */
public CallSite(Class<?> caller, String name, MethodType type) {
this.calleeNameRemoveForPFD = new MemberName(caller, name, type);
}
/** @deprecated transitional form defined in EDR but removed in PFD */
public Class<?> callerClass() {
MemberName callee = this.calleeNameRemoveForPFD;
return callee == null ? null : callee.getDeclaringClass();
}
/** @deprecated transitional form defined in EDR but removed in PFD */
public String name() {
MemberName callee = this.calleeNameRemoveForPFD;
return callee == null ? null : callee.getName();
}
/** @deprecated transitional form defined in EDR but removed in PFD */
public MethodType type() {
MemberName callee = this.calleeNameRemoveForPFD;
return callee == null ? (target == null ? null : target.type()) : callee.getMethodType();
}
/** @deprecated transitional form defined in EDR but removed in PFD */
protected MethodHandle initialTarget() {
return initialTarget(callerClass(), name(), type());
}
/** Report if the JVM has linked this {@code CallSite} object to a dynamic call site instruction.
* Once it is linked, it is never unlinked.
*/
private boolean isLinked() {
return vmmethod != null;
}
/** 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.isLinked()) {
throw new InvokeDynamicBootstrapError("call site has already been linked to an invokedynamic instruction");
}
MethodHandle target = this.target;
if (target == null) {
this.target = target = this.initialTarget(callerMethod.getDeclaringClass(), name, type);
}
if (!target.type().equals(type)) {
throw wrongTargetType(target, type);
}
this.vmindex = callerBCI;
this.vmmethod = callerMethod;
assert(this.isLinked());
}
/**
* Just after a call site is created by a bootstrap method handle,
* if the target has not been initialized by the factory method itself,
* the method {@code initialTarget} is called to produce an initial
* non-null target. (Live call sites must never have null targets.)
* <p>
* The arguments are the same as those passed to the bootstrap method.
* Thus, a bootstrap method is free to ignore the arguments and simply
* create a "blank" {@code CallSite} object of an appropriate subclass.
* <p>
* If the bootstrap method itself does not initialize the call site,
* this method must be overridden, because it just raises an
* {@code InvokeDynamicBootstrapError}, which in turn causes the
* linkage of the {@code invokedynamic} instruction to terminate
* abnormally.
*/
protected MethodHandle initialTarget(Class<?> callerClass, String name, MethodType type) {
throw new InvokeDynamicBootstrapError("target must be initialized before call site is linked: "+name+type);
}
/**
* Report the current linkage state of the call site. (This is mutable.)
* The value may not be null after the {@code CallSite} object is returned
* from the bootstrap method of the {@code invokedynamic} instruction.
* When an {@code invokedynamic} instruction is executed, the target method
* of its associated {@code call site} object is invoked directly,
* as if via {@link MethodHandle}{@code .invoke}.
* <p>
* The interactions of {@code getTarget} with memory are the same
* as of a read from an ordinary variable, such as an array element or a
* non-volatile, non-final field.
* <p>
* In particular, the current thread may choose to reuse the result
* of a previous read of the target from memory, and may fail to see
* a recent update to the target by another thread.
* @return the current linkage state of the call site
* @see #setTarget
*/
public MethodHandle getTarget() {
return target;
}
/**
* Set the target method of this call site.
* <p>
* The interactions of {@code setTarget} with memory are the same
* as of a write to an ordinary variable, such as an array element or a
* non-volatile, non-final field.
* <p>
* In particular, unrelated threads may fail to see the updated target
* until they perform a read from memory.
* Stronger guarantees can be created by putting appropriate operations
* into the bootstrap method and/or the target methods used
* at any given call site.
* @param newTarget the new target
* @throws NullPointerException if the proposed new target is null
* @throws WrongMethodTypeException if the call site is linked and the proposed new target
* has a method type that differs from the previous target
*/
public void setTarget(MethodHandle newTarget) {
MethodType newType = newTarget.type(); // null check!
MethodHandle oldTarget = this.target;
if (oldTarget == null) {
// CallSite is not yet linked.
assert(!isLinked());
this.target = newTarget; // might be null!
return;
}
MethodType oldType = oldTarget.type();
if (!newTarget.type().equals(oldType))
throw wrongTargetType(newTarget, oldType);
if (oldTarget != newTarget)
CallSiteImpl.setCallSiteTarget(IMPL_TOKEN, this, newTarget);
}
private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {
return new WrongMethodTypeException(String.valueOf(target)+target.type()+" should be of type "+type);
}
/** Produce a printed representation that displays information about this call site
* that may be useful to the human reader.
*/
@Override
public String toString() {
StringBuilder buf = new StringBuilder("CallSite#");
buf.append(hashCode());
if (!isLinked())
buf.append("[unlinked]");
else
buf.append("[")
.append("from ").append(vmmethod.getDeclaringClass().getName())
.append(" : ").append(getTarget().type())
.append(" => ").append(getTarget())
.append("]");
return buf.toString();
}
}