Module java.base
Package java.lang.invoke

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.

    Since:
    1.7
    See Also:
    MutableCallSite

    • 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