VolatileCallSite (Java Platform SE 8 )
Keywords: java.lang.invoke.VolatileCallSite class
Date: 2018-07-01

compact1, compact2, compact3
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

    All Methods Instance Methods Concrete 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

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