MutableCallSite Class

Definition

[Android.Runtime.Register("java/lang/invoke/MutableCallSite", ApiSince=26, DoNotGenerateAcw=true)]
public class MutableCallSite : Java.Lang.Invoke.CallSite

[<Android.Runtime.Register("java/lang/invoke/MutableCallSite", ApiSince=26, DoNotGenerateAcw=true)>]
type MutableCallSite = class
    inherit CallSite

Inheritance

Object

Object

CallSite

MutableCallSite

Attributes

RegisterAttribute

Remarks

A MutableCallSite is a CallSite whose target variable behaves like an ordinary field. An invokedynamic instruction linked to a MutableCallSite delegates all calls to the site's current target. The CallSite#dynamicInvoker dynamic invoker of a mutable call site also delegates each call to the site's current target.

Here is an example of a mutable call site which introduces a state variable into a method handle chain. <!-- JavaDocExamplesTest.testMutableCallSite --> <blockquote>

{@code
            MutableCallSite name = new MutableCallSite(MethodType.methodType(String.class));
            MethodHandle MH_name = name.dynamicInvoker();
            MethodType MT_str1 = MethodType.methodType(String.class);
            MethodHandle MH_upcase = MethodHandles.lookup()
                .findVirtual(String.class, "toUpperCase", MT_str1);
            MethodHandle worker1 = MethodHandles.filterReturnValue(MH_name, MH_upcase);
            name.setTarget(MethodHandles.constant(String.class, "Rocky"));
            assertEquals("ROCKY", (String) worker1.invokeExact());
            name.setTarget(MethodHandles.constant(String.class, "Fred"));
            assertEquals("FRED", (String) worker1.invokeExact());
            // (mutation can be continued indefinitely)
            }

</blockquote>

The same call site may be used in several places at once. <blockquote>

{@code
            MethodType MT_str2 = MethodType.methodType(String.class, String.class);
            MethodHandle MH_cat = lookup().findVirtual(String.class,
              "concat", methodType(String.class, String.class));
            MethodHandle MH_dear = MethodHandles.insertArguments(MH_cat, 1, ", dear?");
            MethodHandle worker2 = MethodHandles.filterReturnValue(MH_name, MH_dear);
            assertEquals("Fred, dear?", (String) worker2.invokeExact());
            name.setTarget(MethodHandles.constant(String.class, "Wilma"));
            assertEquals("WILMA", (String) worker1.invokeExact());
            assertEquals("Wilma, dear?", (String) worker2.invokeExact());
            }

</blockquote>

<em>Non-synchronization of target values:</em> A write to a mutable call site's target does not force other threads to become aware of the updated value. Threads which do not perform suitable synchronization actions relative to the updated call site may cache the old target value and delay their use of the new target value indefinitely. (This is a normal consequence of the Java Memory Model as applied to object fields.)

For target values which will be frequently updated, consider using a VolatileCallSite volatile call site instead.

Java documentation for java.lang.invoke.MutableCallSite.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.