Module java.base
Package java.lang.invoke

# Class VolatileCallSite

java.lang.Object
java.lang.invoke.CallSite
java.lang.invoke.VolatileCallSite

public non-sealed 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`.

Since:
  1.7
See Also:
  - `MutableCallSite`

- ## Constructor Summary

  Constructors
  Constructor
  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

  Modifier and Type
  Method
  Description
  `final MethodHandle`
  `dynamicInvoker()`
  Produces a method handle equivalent to an invokedynamic instruction which has been linked to this call site.
  `final 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 declared in class java.lang.invoke.CallSite

  `type`

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### 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 Details

  - ### 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