6964498: JSR 292 invokedynamic sites need local bootstrap methods
Summary: Add JVM_CONSTANT_InvokeDynamic records to constant pool to determine per-instruction BSMs; add MethodHandleProvider.
Reviewed-by: twisti
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package java.dyn;
/**
* An interface for an object to provide a target {@linkplain MethodHandle method handle} to a {@code invokedynamic} instruction.
* There are many function-like objects in various Java APIs.
* This interface provides a standard way for such function-like objects to be bound
* to a dynamic call site, by providing a view of their behavior in the form of a low-level method handle.
* <p>
* The type {@link MethodHandle} is a concrete class whose implementation
* hierarchy (if any) may be tightly coupled to the underlying JVM implementation.
* It cannot also serve as a base type for user-defined functional APIs.
* For this reason, {@code MethodHandle} cannot be subclassed to add new
* behavior to method handles. But this interface can be used to provide
* a link between a user-defined function and the {@code invokedynamic}
* instruction and the method handle API.
*/
public interface MethodHandleProvider {
/** Produce a method handle which will serve as a behavioral proxy for the current object.
* The type and invocation behavior of the proxy method handle are user-defined,
* and should have some relation to the intended meaning of the original object itself.
* <p>
* The current object may have a changeable behavior.
* For example, {@link CallSite} has a {@code setTarget} method which changes its invocation.
* In such a case, it is <em>incorrect</em> for {@code asMethodHandle} to return
* a method handle whose behavior may diverge from that of the current object.
* Rather, the returned method handle must stably and permanently access
* the behavior of the current object, even if that behavior is changeable.
* <p>
* The reference identity of the proxy method handle is not guaranteed to
* have any particular relation to the reference identity of the object.
* In particular, several objects with the same intended meaning could
* share a common method handle, or the same object could return different
* method handles at different times. In the latter case, the different
* method handles should have the same type and invocation behavior,
* and be usable from any thread at any time.
* In particular, if a MethodHandleProvider is bound to an <code>invokedynamic</code>
* call site, the proxy method handle extracted at the time of binding
* will be used for an unlimited time, until the call site is rebound.
* <p>
* The type {@link MethodHandle} itself implements {@code MethodHandleProvider}, and
* for this method simply returns {@code this}.
*/
public MethodHandle asMethodHandle();
/** Produce a method handle of a given type which will serve as a behavioral proxy for the current object.
* As for the no-argument version {@link #asMethodHandle()}, the invocation behavior of the
* proxy method handle is user-defined. But the type must be the given type,
* or else a {@link WrongMethodTypeException} must be thrown.
* <p>
* If the current object somehow represents a variadic or overloaded behavior,
* the method handle returned for a given type might represent only a subset of
* the current object's repertoire of behaviors, which correspond to that type.
*/
public MethodHandle asMethodHandle(MethodType type) throws WrongMethodTypeException;
}