Module java.base
Package 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.

Since:
1.7
See Also:
MutableCallSite

  • 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