CallSite (Java Platform SE 7 b118)

спецификации, руководства, описания, API

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Java™ Platform
Standard Ed. 7
DRAFT ea-b118

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java.dyn
Class CallSite

java.lang.Object
  java.dyn.CallSite

All Implemented Interfaces:: MethodHandleProvider

Direct Known Subclasses:: ConstantCallSite

public class CallSite
extends Object
implements MethodHandleProvider

A CallSite is a holder for a variable MethodHandle, which is called its target. Every call to a CallSite is delegated to the site's current target.

A call site is initially created in an unlinked state, which is distinguished by a null target variable. Before the call site may be invoked (and before certain other operations are attempted), the call site must be linked to a non-null target.

A call site may be relinked by changing its target. The new target must be non-null and must have the same type as the previous target. Thus, though a call site can be relinked to a series of successive targets, it cannot change its type.

Linkage happens once in the lifetime of any given CallSite object. Because of call site invalidation, this linkage can be repeated for a single invokedynamic instruction, with multiple CallSite objects. When a CallSite is unlinked from an invokedynamic instruction, the instruction is reset so that it is no longer associated with the CallSite object, but the CallSite does not change state.

Here is a sample use of call sites and bootstrap methods which links every dynamic call site to print its arguments:


@BootstrapMethod(value=PrintArgsDemo.class, name="bootstrapDynamic")
static void test() throws Throwable {
    InvokeDynamic.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(Class caller, String name, MethodType type) {
  // ignore caller and name, but match the type:
  return new CallSite(MethodHandles.collectArguments(printArgs, type));
}

Constructor Summary
Constructor and Description
`CallSite()` Make a blank call site object.
`CallSite(Class<?> caller, String name, MethodType type)` Deprecated. transitional form defined in EDR but removed in PFD
`CallSite(MethodHandle target)` Make a blank call site object, possibly equipped with an initial target method handle.

Method Summary
Modifier and Type	Method and Description
`MethodHandle`	`asMethodHandle()` Implementation of `MethodHandleProvider` which returns `this.dynamicInvoker()`.
`MethodHandle`	`asMethodHandle(MethodType type)` Implementation of `MethodHandleProvider`, which returns `this.dynamicInvoker().asType(type)`.
`Class<?>`	`callerClass()` Deprecated. transitional form defined in EDR but removed in PFD
`MethodHandle`	`dynamicInvoker()` PROVISIONAL API, WORK IN PROGRESS: Produce a method handle equivalent to an invokedynamic instruction which has been linked to this call site.
`MethodHandle`	`getTarget()` Report the current linkage state of the call site.
`protected MethodHandle`	`initialTarget()` Deprecated. transitional form defined in EDR but removed in PFD
`protected MethodHandle`	`initialTarget(Class<?> callerClass, String name, MethodType type)` Deprecated. transitional form defined in EDR but removed in PFD
`String`	`name()` Deprecated. transitional form defined in EDR but removed in PFD
`void`	`setTarget(MethodHandle newTarget)` Set the target method of this call site.
`String`	`toString()` Produce a printed representation that displays information about this call site that may be useful to the human reader.
`MethodType`	`type()` Deprecated. transitional form defined in EDR but removed in PFD

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

CallSite

public CallSite()

Make a blank call site object. Before it is returned from a bootstrap method, this CallSite object must be provided with a target method via a call to setTarget, or by a subclass override of initialTarget.

CallSite

public CallSite(MethodHandle target)

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 CallSite object must be provided with a target method via a call to setTarget(java.dyn.MethodHandle), or by a subclass override of initialTarget().

Parameters:: target - the method handle which will be the initial target of the call site, or null if there is none yet