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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.lang.invoke;
/**
* A {@code VolatileCallSite} is a {@link CallSite} whose target acts like a volatile variable.
* An {@code invokedynamic} instruction linked to a {@code VolatileCallSite} sees updates
* to its call site target immediately, even if the update occurs in another thread.
* There may be a performance penalty for such tight coupling between threads.
* <p>
* Unlike {@code MutableCallSite}, there is no
* {@linkplain MutableCallSite#syncAll syncAll operation} on volatile
* call sites, since every write to a volatile variable is implicitly
* synchronized with reader threads.
* <p>
* In other respects, a {@code VolatileCallSite} is interchangeable
* with {@code MutableCallSite}.
* @see MutableCallSite
* @author John Rose, JSR 292 EG
*/
public class VolatileCallSite extends CallSite {
/**
* Creates a call site with a volatile binding to its target.
* The initial target is set to a method handle
* of the given type which will throw an {@code IllegalStateException} if called.
* @param type the method type that this call site will have
* @throws NullPointerException if the proposed type is null
*/
public VolatileCallSite(MethodType type) {
super(type);
}
/**
* Creates a call site with a volatile binding to its target.
* The target is set to the given value.
* @param target the method handle that will be the initial target of the call site
* @throws NullPointerException if the proposed target is null
*/
public VolatileCallSite(MethodHandle target) {
super(target);
}
/**
* Returns the target method of the call site, which behaves
* like a {@code volatile} field of the {@code VolatileCallSite}.
* <p>
* The interactions of {@code getTarget} with memory are the same
* as of a read from a {@code volatile} field.
* <p>
* In particular, the current thread is required to issue a fresh
* read of the target from memory, and must not fail to see
* a recent update to the target by another thread.
*
* @return the linkage state of this call site, a method handle which can change over time
* @see #setTarget
*/
@Override public final MethodHandle getTarget() {
return getTargetVolatile();
}
/**
* Updates the target method of this call site, as a volatile variable.
* The type of the new target must agree with the type of the old target.
* <p>
* The interactions with memory are the same as of a write to a volatile field.
* In particular, any threads is guaranteed to see the updated target
* the next time it calls {@code getTarget}.
* @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 #getTarget
*/
@Override public void setTarget(MethodHandle newTarget) {
checkTargetChange(getTargetVolatile(), newTarget);
setTargetVolatile(newTarget);
}
/**
* {@inheritDoc}
*/
@Override
public final MethodHandle dynamicInvoker() {
return makeDynamicInvoker();
}
}