java.lang.invoke

Class VolatileCallSite

java.lang.Object

java.lang.invoke.CallSite

java.lang.invoke.VolatileCallSite

public class VolatileCallSite
extends CallSite

A VolatileCallSite is a CallSite whose target acts like a volatile variable. An invokedynamic instruction linked to a 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.

Unlike MutableCallSite, there is no syncAll operation on volatile call sites, since every write to a volatile variable is implicitly synchronized with reader threads.

In other respects, a VolatileCallSite is interchangeable with MutableCallSite.

See Also:

MutableCallSite

Constructor Summary

Constructors

Constructor and Description
VolatileCallSite(MethodHandle target) Creates a call site with a volatile binding to its target.
VolatileCallSite(MethodType type) Creates a call site with a volatile binding to its target.

Method Summary

Methods

Modifier and Type	Method and Description
MethodHandle	dynamicInvoker() Produces a method handle equivalent to an invokedynamic instruction which has been linked to this call site.
MethodHandle	getTarget() Returns the target method of the call site, which behaves like a volatile field of the VolatileCallSite.
void	setTarget(MethodHandle newTarget) Updates the target method of this call site, as a volatile variable.

Methods inherited from class java.lang.invoke.CallSite

type

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

VolatileCallSite

public VolatileCallSite(MethodType type)

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 IllegalStateException if called.

Parameters:

type - the method type that this call site will have

Throws:

NullPointerException - if the proposed type is null

VolatileCallSite

public VolatileCallSite(MethodHandle target)

Creates a call site with a volatile binding to its target. The target is set to the given value.

Parameters:

target - the method handle that will be the initial target of the call site

Throws:

NullPointerException - if the proposed target is null

Method Detail

getTarget

public final MethodHandle getTarget()

Returns the target method of the call site, which behaves like a volatile field of the VolatileCallSite.

The interactions of getTarget with memory are the same as of a read from a volatile field.

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.

Specified by:

getTarget in class CallSite

Returns:

the linkage state of this call site, a method handle which can change over time

See Also:

setTarget(java.lang.invoke.MethodHandle)

setTarget

public void setTarget(MethodHandle newTarget)

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.

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 getTarget.

Specified by:

setTarget in class CallSite

Parameters:

newTarget - the new target

Throws:

NullPointerException - if the proposed new target is null

WrongMethodTypeException - if the proposed new target has a method type that differs from the previous target

See Also:

getTarget()

dynamicInvoker

public final MethodHandle dynamicInvoker()

Produces a method handle equivalent to an invokedynamic instruction which has been linked to this call site.

This method is equivalent to the following 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)
 

Specified by:

dynamicInvoker in class CallSite

Returns:

a method handle which always invokes this call site's current target