Examples of SwitchPoint

java.lang.invoke.SwitchPoint
following steps may be repeated to re-use the same switch point: MethodHandle worker1 = MH_strcat; MethodHandle worker2 = MethodHandles.permuteArguments(MH_strcat, MH_strcat.type(), 1, 0); MethodHandle worker = spt.guardWithTest(worker1, worker2); assertEquals("method", (String) worker.invokeExact("met", "hod"));}SwitchPoint.invalidateAll(new SwitchPoint[] spt }); assert(spt.hasBeenInvalidated()); assertEquals("hodmet", (String) worker.invokeExact("met", "hod")); }
Discussion: Switch points are useful without subclassing. They may also be subclassed. This may be useful in order to associate application-specific invalidation logic with the switch point. Notice that there is no permanent association between a switch point and the method handles it produces and consumes. The garbage collector may collect method handles produced or consumed by a switch point independently of the lifetime of the switch point itself.
Implementation Note: A switch point behaves as if implemented on top of {@link MutableCallSite}, approximately as follows:
```
 {@code}public class SwitchPoint  private static final MethodHandle K_true  = MethodHandles.constant(boolean.class, true), K_false = MethodHandles.constant(boolean.class, false); private final MutableCallSite mcs; private final MethodHandle mcsInvoker; public SwitchPoint() { this.mcs = new MutableCallSite(K_true); this.mcsInvoker = mcs.dynamicInvoker(); } public MethodHandle guardWithTest( MethodHandle target, MethodHandle fallback) { // Note:  mcsInvoker is of type ()boolean. // Target and fallback may take any arguments, but must have the same type. return MethodHandles.guardWithTest(this.mcsInvoker, target, fallback); } public static void invalidateAll(SwitchPoint[] spts) { List<MutableCallSite> mcss = new ArrayList<>(); for (SwitchPoint spt : spts)  mcss.add(spt.mcs); for (MutableCallSite mcs : mcss)  mcs.setTarget(K_false); MutableCallSite.syncAll(mcss.toArray(new MutableCallSite[0])); } } }
```
@author Remi Forax, JSR 292 EG

Examples of java.lang.invoke.SwitchPoint

    ///////////////////////////////////////////////////////////////////////////
    // constant lookup


    public static IRubyObject searchConst(MutableCallSite site, String constName, ThreadContext context, StaticScope staticScope) throws Throwable {
        Ruby runtime = context.runtime;
        SwitchPoint switchPoint = (SwitchPoint)runtime.getConstantInvalidator().getData();
        IRubyObject value = staticScope.getConstant(constName);


        if (value == null) {
            return staticScope.getModule().callMethod(context, "const_missing", runtime.fastNewSymbol(constName));
        }


        // bind constant until invalidated
        MethodHandle target = Binder.from(site.type())
                .drop(0, 2)
                .constant(value);
        MethodHandle fallback = Binder.from(site.type())
                .insert(0, site, constName)
                .invokeStatic(MethodHandles.lookup(), Bootstrap.class, "searchConst");


        site.setTarget(switchPoint.guardWithTest(target, fallback));


        return value;
    }

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Examples of java.lang.invoke.SwitchPoint

    
    public synchronized void invalidate() {
        if (switchPoint == DUMMY) return;


        SwitchPoint.invalidateAll(new SwitchPoint[]{switchPoint});
        switchPoint = new SwitchPoint();
    }

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Examples of java.lang.invoke.SwitchPoint

        
        SwitchPoint.invalidateAll(switchPoints);
    }
    
    public synchronized Object getData() {
        return switchPoint == DUMMY ? switchPoint = new SwitchPoint() : switchPoint;
    }

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Examples of java.lang.invoke.SwitchPoint

    }
    
    public synchronized SwitchPoint replaceSwitchPoint() {
        if (switchPoint == DUMMY) return switchPoint;


        SwitchPoint oldSwitchPoint = switchPoint;
        switchPoint = new SwitchPoint();
        return oldSwitchPoint;
    }

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Examples of java.lang.invoke.SwitchPoint

    // INITIAL AND FALLBACK METHODS FOR POST BOOTSTRAP
    ////////////////////////////////////////////////////////////////////////////
    
    public static IRubyObject constantFallback(RubyConstantCallSite site, 
            AbstractScript script, ThreadContext context, int scopeIndex) {
        SwitchPoint switchPoint = (SwitchPoint)context.runtime.getConstantInvalidator(site.name()).getData();
        StaticScope scope = script.getScope(scopeIndex);
        IRubyObject value = scope.getConstant(site.name());
        
        if (value != null) {
            if (Options.INVOKEDYNAMIC_LOG_CONSTANTS.load()) LOG.info("constant " + site.name() + " bound directly");
            
            MethodHandle valueHandle = constant(IRubyObject.class, value);
            valueHandle = dropArguments(valueHandle, 0, AbstractScript.class, ThreadContext.class);


            MethodHandle fallback = insertArguments(
                    findStatic(InvokeDynamicSupport.class, "constantFallback",
                    methodType(IRubyObject.class, RubyConstantCallSite.class, AbstractScript.class, ThreadContext.class, int.class)),
                    0,
                    site);
            fallback = insertArguments(fallback, 2, scopeIndex);


            MethodHandle gwt = switchPoint.guardWithTest(valueHandle, fallback);
            site.setTarget(gwt);
        } else {
            value = scope.getModule()
                    .callMethod(context, "const_missing", context.runtime.newSymbol(site.name()));
        }

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Examples of java.lang.invoke.SwitchPoint

        return value;
    }


    public static boolean constantBooleanFallback(RubyConstantCallSite site, 
            AbstractScript script, ThreadContext context, int scopeIndex) {
        SwitchPoint switchPoint = (SwitchPoint)context.runtime.getConstantInvalidator(site.name()).getData();
        StaticScope scope = script.getScope(scopeIndex);
        IRubyObject value = scope.getConstant(site.name());
        
        if (value != null) {
            if (Options.INVOKEDYNAMIC_LOG_CONSTANTS.load()) LOG.info("constant " + site.name() + " bound directly");
            
            MethodHandle valueHandle = constant(boolean.class, value.isTrue());
            valueHandle = dropArguments(valueHandle, 0, AbstractScript.class, ThreadContext.class);


            MethodHandle fallback = insertArguments(
                    findStatic(InvokeDynamicSupport.class, "constantBooleanFallback",
                    methodType(boolean.class, RubyConstantCallSite.class, AbstractScript.class, ThreadContext.class, int.class)),
                    0,
                    site);
            fallback = insertArguments(fallback, 2, scopeIndex);


            MethodHandle gwt = switchPoint.guardWithTest(valueHandle, fallback);
            site.setTarget(gwt);
        } else {
            value = scope.getModule()
                    .callMethod(context, "const_missing", context.runtime.newSymbol(site.name()));
        }

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Examples of java.lang.invoke.SwitchPoint

            switchPoint = DUMMY;
            return;
        }
        
        SwitchPoint.invalidateAll(new SwitchPoint[]{switchPoint});
        switchPoint = new SwitchPoint();
    }

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Examples of java.lang.invoke.SwitchPoint

        
        SwitchPoint.invalidateAll(switchPoints);
    }
    
    public synchronized Object getData() {
        return switchPoint == DUMMY && failures <= maxFailures ? switchPoint = new SwitchPoint() : switchPoint;
    }

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Examples of java.lang.invoke.SwitchPoint

    }
    
    public synchronized SwitchPoint replaceSwitchPoint() {
        if (switchPoint == DUMMY || failures > maxFailures) return DUMMY;


        SwitchPoint oldSwitchPoint = switchPoint;
        switchPoint = new SwitchPoint();
        return oldSwitchPoint;
    }

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Examples of java.lang.invoke.SwitchPoint

    
    public synchronized void invalidate() {
        if (switchPoint == DUMMY) return;


        SwitchPoint.invalidateAll(new SwitchPoint[]{switchPoint});
        switchPoint = new SwitchPoint();
    }

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