Class 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

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.

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

Constructors

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

Methods

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

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https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/VolatileCallSite.html