Java MethodHandles.foldArguments方法代码示例

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
/**
 * Creates the {@link MethodHandle} for the megamorphic call site
 * using {@link ClassValue} and {@link MethodHandles#exactInvoker(MethodType)}:
 */
private MethodHandle createMegamorphicHandle() {
    final MethodType type = type();
    final ClassValue<MethodHandle> megamorphicCache = new ClassValue<MethodHandle>() {
        @Override
        protected MethodHandle computeValue(Class<?> receiverType) {
            // it's too stupid that we cannot throw checked exceptions... (use rethrow puzzler):
            try {
                return lookup(flavor, name, receiverType).asType(type);
            } catch (Throwable t) {
                Def.rethrow(t);
                throw new AssertionError();
            }
        }
    };
    return MethodHandles.foldArguments(MethodHandles.exactInvoker(type),
            MEGAMORPHIC_LOOKUP.bindTo(megamorphicCache));            
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public void testReturnOnStack() throws Throwable {
    MethodHandles.Lookup l = MethodHandles.lookup();

    MethodHandle consumeIdentity = l.findStatic(
            PermuteArgsReturnVoidTest.class, "consumeIdentity",
            MethodType.methodType(String.class, String.class, int.class, int.class));
    MethodHandle consumeVoid = l.findStatic(
            PermuteArgsReturnVoidTest.class, "consumeVoid",
            MethodType.methodType(void.class, String.class, int.class, int.class));

    MethodHandle f = MethodHandles.foldArguments(consumeIdentity, consumeVoid);

    MethodHandle p = MethodHandles.permuteArguments(f, MethodType.methodType(String.class, String.class, int.class, int.class), 0, 2, 1);

    String s = (String) p.invoke("IN", 0, 0);
    Assert.assertEquals(s.getClass(), String.class);
    Assert.assertEquals(s, "IN");
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public void testReturnFromArg() throws Throwable {
    MethodHandles.Lookup l = MethodHandles.lookup();

    MethodHandle consumeIdentity = dropArguments(
            identity(String.class), 1, int.class, int.class);
    MethodHandle consumeVoid = l.findStatic(
            PermuteArgsReturnVoidTest.class, "consumeVoid",
            MethodType.methodType(void.class, String.class, int.class, int.class));

    MethodHandle f = MethodHandles.foldArguments(consumeIdentity, consumeVoid);

    MethodHandle p = MethodHandles.permuteArguments(f, MethodType.methodType(String.class, String.class, int.class, int.class), 0, 2, 1);

    String s = (String) p.invoke("IN", 0, 0);
    Assert.assertEquals(s.getClass(), String.class);
    Assert.assertEquals(s, "IN");
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
/** Looks up generic method, with a dynamic cast to the receiver's type. (compound assignment) */
public static MethodHandle dynamicCast(MethodHandle target) {
    // adapt dynamic receiver cast to the generic method
    MethodHandle cast = DYNAMIC_RECEIVER_CAST.asType(MethodType.methodType(target.type().returnType(), 
                                                                  target.type().returnType(),
                                                                  target.type().parameterType(0)));
    // drop the RHS parameter
    cast = MethodHandles.dropArguments(cast, 2, target.type().parameterType(1));
    // combine: f(x,y) -> g(f(x,y), x, y);
    return MethodHandles.foldArguments(cast, target);
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
private MethodHandle createRelinkAndInvokeMethod(final RelinkableCallSite callSite, final int relinkCount) {
    // Make a bound MH of invoke() for this linker and call site
    final MethodHandle boundRelinker = MethodHandles.insertArguments(RELINK, 0, this, callSite, Integer.valueOf(
            relinkCount));
    // Make a MH that gathers all arguments to the invocation into an Object[]
    final MethodType type = callSite.getDescriptor().getMethodType();
    final MethodHandle collectingRelinker = boundRelinker.asCollector(Object[].class, type.parameterCount());
    return MethodHandles.foldArguments(MethodHandles.exactInvoker(type), collectingRelinker.asType(
            type.changeReturnType(MethodHandle.class)));
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
OverloadedMethod(final List<MethodHandle> methodHandles, final OverloadedDynamicMethod parent, final MethodType callSiteType,
        final LinkerServices linkerServices) {
    this.parent = parent;
    final Class<?> commonRetType = getCommonReturnType(methodHandles);
    this.callSiteType = callSiteType.changeReturnType(commonRetType);
    this.linkerServices = linkerServices;

    fixArgMethods = new ArrayList<>(methodHandles.size());
    varArgMethods = new ArrayList<>(methodHandles.size());
    final int argNum = callSiteType.parameterCount();
    for(MethodHandle mh: methodHandles) {
        if(mh.isVarargsCollector()) {
            final MethodHandle asFixed = mh.asFixedArity();
            if(argNum == asFixed.type().parameterCount()) {
                fixArgMethods.add(asFixed);
            }
            varArgMethods.add(mh);
        } else {
            fixArgMethods.add(mh);
        }
    }
    fixArgMethods.trimToSize();
    varArgMethods.trimToSize();

    final MethodHandle bound = SELECT_METHOD.bindTo(this);
    final MethodHandle collecting = SingleDynamicMethod.collectArguments(bound, argNum).asType(
            callSiteType.changeReturnType(MethodHandle.class));
    invoker = MethodHandles.foldArguments(MethodHandles.exactInvoker(this.callSiteType), collecting);
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
/**
 * Creates a method that rebuilds our call chain, pruning it of any invalidated switchpoints, and then invokes that
 * chain.
 * @param relink the ultimate fallback for the chain (the {@code DynamicLinker}'s relink).
 * @return a method handle for prune-and-invoke
 */
private MethodHandle makePruneAndInvokeMethod(final MethodHandle relink, final MethodHandle prune) {
    // Bind prune to (this, relink)
    final MethodHandle boundPrune = MethodHandles.insertArguments(prune, 0, this, relink);
    // Make it ignore all incoming arguments
    final MethodHandle ignoreArgsPrune = MethodHandles.dropArguments(boundPrune, 0, type().parameterList());
    // Invoke prune, then invoke the call site target with original arguments
    return MethodHandles.foldArguments(MethodHandles.exactInvoker(type()), ignoreArgsPrune);
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public static void testFold0a() throws Throwable {
    // equivalence to foldArguments(MethodHandle,MethodHandle)
    MethodHandle fold = MethodHandles.foldArguments(Fold.MH_multer, 0, Fold.MH_adder);
    assertEquals(Fold.MT_folded1, fold.type());
    assertEquals(720, (int) fold.invoke(3, 4, 5));
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public static void testFold1a() throws Throwable {
    // test foldArguments for folding position 1
    MethodHandle fold = MethodHandles.foldArguments(Fold.MH_multer, 1, Fold.MH_adder1);
    assertEquals(Fold.MT_folded1, fold.type());
    assertEquals(540, (int) fold.invoke(3, 4, 5));
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public static void testFold0b() throws Throwable {
    // test foldArguments equivalence with multiple types
    MethodHandle fold = MethodHandles.foldArguments(Fold.MH_str, 0, Fold.MH_comb);
    assertEquals(Fold.MT_folded2, fold.type());
    assertEquals(23, (int) fold.invoke("true", true, 23));
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public static void testFold1b() throws Throwable {
    // test folgArguments for folding position 1, with multiple types
    MethodHandle fold = MethodHandles.foldArguments(Fold.MH_str, 1, Fold.MH_comb2);
    assertEquals(Fold.MT_folded3, fold.type());
    assertEquals(1, (int) fold.invoke(true, true, 1));
    assertEquals(-1, (int) fold.invoke(true, false, -1));
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Test
public static void testFoldArgumentsExample() throws Throwable {
    // test the JavaDoc foldArguments-with-pos example
    StringWriter swr = new StringWriter();
    MethodHandle trace = LOOKUP.findVirtual(StringWriter.class, "write", methodType(void.class, String.class)).bindTo(swr);
    MethodHandle cat = LOOKUP.findVirtual(String.class, "concat", methodType(String.class, String.class));
    assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
    MethodHandle catTrace = MethodHandles.foldArguments(cat, 1, trace);
    assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
    assertEquals("jum", swr.toString());
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
/**
 * Creates a method that rebuilds our call chain, pruning it of any invalidated switchpoints, and then invokes that
 * chain.
 * @param relinkAndInvoke the ultimate fallback for the chain passed from the dynamic linker.
 * @return a method handle for prune-and-invoke
 */
private MethodHandle makePruneAndInvokeMethod(final MethodHandle relinkAndInvoke, final MethodHandle prune) {
    // Bind prune to (this, relink)
    final MethodHandle boundPrune = MethodHandles.insertArguments(prune, 0, this, relinkAndInvoke);
    // Make it ignore all incoming arguments
    final MethodHandle ignoreArgsPrune = MethodHandles.dropArguments(boundPrune, 0, type().parameterList());
    // Invoke prune, then invoke the call site target with original arguments
    return MethodHandles.foldArguments(MethodHandles.exactInvoker(type()), ignoreArgsPrune);
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
@Override
public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest, final LinkerServices linkerServices)
        throws Exception {
    final Object objSuperAdapter = linkRequest.getReceiver();
    if(!(objSuperAdapter instanceof JavaSuperAdapter)) {
        return null;
    }

    final CallSiteDescriptor descriptor = linkRequest.getCallSiteDescriptor();
    if(!CallSiteDescriptorFactory.tokenizeOperators(descriptor).contains(GET_METHOD)) {
        // We only handle getMethod
        return null;
    }

    final Object adapter = ((JavaSuperAdapter)objSuperAdapter).getAdapter();

    // Replace argument (javaSuperAdapter, ...) => (adapter, ...) when delegating to BeansLinker
    final Object[] args = linkRequest.getArguments();
    args[0] = adapter;

    // Use R(T0, ...) => R(adapter.class, ...) call site type when delegating to BeansLinker.
    final MethodType type = descriptor.getMethodType();
    final Class<?> adapterClass = adapter.getClass();
    final boolean hasFixedName = descriptor.getNameTokenCount() > 2;
    final String opName = hasFixedName ? (DYN_GET_METHOD_FIXED + descriptor.getNameToken(
            CallSiteDescriptor.NAME_OPERAND)) : DYN_GET_METHOD;

    final CallSiteDescriptor newDescriptor = NashornCallSiteDescriptor.get(descriptor.getLookup(), opName,
            type.changeParameterType(0, adapterClass), 0);

    // Delegate to BeansLinker
    final GuardedInvocation guardedInv = NashornBeansLinker.getGuardedInvocation(
            BeansLinker.getLinkerForClass(adapterClass), linkRequest.replaceArguments(newDescriptor, args),
            linkerServices);

    final MethodHandle guard = IS_ADAPTER_OF_CLASS.bindTo(adapterClass);
    if(guardedInv == null) {
        // Short circuit the lookup here for non-existent methods by linking an empty getter. If we just returned
        // null instead, BeansLinker would find final methods on the JavaSuperAdapter instead: getClass() and
        // wait().
        return new GuardedInvocation(MethodHandles.dropArguments(EMPTY_GETTER, 1,type.parameterList().subList(1,
                type.parameterCount())), guard).asType(descriptor);
    }

    final MethodHandle invocation = guardedInv.getInvocation();
    final MethodType invType = invocation.type();
    // For invocation typed R(T0, ...) create a dynamic method binder of type Object(R, T0)
    final MethodHandle typedBinder = BIND_DYNAMIC_METHOD.asType(MethodType.methodType(Object.class,
            invType.returnType(), invType.parameterType(0)));
    // For invocation typed R(T0, T1, ...) create a dynamic method binder of type Object(R, T0, T1, ...)
    final MethodHandle droppingBinder = MethodHandles.dropArguments(typedBinder, 2,
            invType.parameterList().subList(1, invType.parameterCount()));
    // Finally, fold the invocation into the binder to produce a method handle that will bind every returned
    // DynamicMethod object from dyn:getMethod calls to the actual receiver
    // Object(R(T0, T1, ...), T0, T1, ...)
    final MethodHandle bindingInvocation = MethodHandles.foldArguments(droppingBinder, invocation);

    final MethodHandle typedGetAdapter = asFilterType(GET_ADAPTER, 0, invType, type);
    final MethodHandle adaptedInvocation;
    if(hasFixedName) {
        adaptedInvocation = MethodHandles.filterArguments(bindingInvocation, 0, typedGetAdapter);
    } else {
        // Add a filter that'll prepend "super$" to each name passed to the variable-name "dyn:getMethod".
        final MethodHandle typedAddPrefix = asFilterType(ADD_PREFIX_TO_METHOD_NAME, 1, invType, type);
        adaptedInvocation = MethodHandles.filterArguments(bindingInvocation, 0, typedGetAdapter, typedAddPrefix);
    }

    return guardedInv.replaceMethods(adaptedInvocation, guard).asType(descriptor);
}
 

import java.lang.invoke.MethodHandles; //导入方法依赖的package包/类
private GuardedInvocationComponent getPropertySetter(final CallSiteDescriptor callSiteDescriptor,
        final LinkerServices linkerServices, final List<String> operations) throws Exception {
    switch(callSiteDescriptor.getNameTokenCount()) {
        case 2: {
            // Must have three arguments: target object, property name, and property value.
            assertParameterCount(callSiteDescriptor, 3);

            // We want setters that conform to "Object(O, V)". Note, we aren't doing "R(O, V)" as it might not be
            // valid for us to convert return values proactively. Also, since we don't know what setters will be
            // invoked, we'll conservatively presume Object return type. The one exception is void return.
            final MethodType origType = callSiteDescriptor.getMethodType();
            final MethodType type = origType.returnType() == void.class ? origType : origType.changeReturnType(Object.class);

            // What's below is basically:
            //   foldArguments(guardWithTest(isNotNull, invoke, null|nextComponent.invocation),
            //     get_setter_handle(type, linkerServices))
            // only with a bunch of method signature adjustments. Basically, retrieve method setter
            // MethodHandle; if it is non-null, invoke it, otherwise either return null, or delegate to next
            // component's invocation.

            // Call site type is "ret_type(object_type,property_name_type,property_value_type)", which we'll
            // abbreviate to R(O, N, V) going forward, although we don't really use R here (see above about using
            // Object return type).
            final MethodType setterType = type.dropParameterTypes(1, 2);
            // Bind property setter handle to the expected setter type and linker services. Type is
            // MethodHandle(Object, String, Object)
            final MethodHandle boundGetter = MethodHandles.insertArguments(getPropertySetterHandle, 0,
                    callSiteDescriptor.changeMethodType(setterType), linkerServices);

            // Cast getter to MethodHandle(O, N, V)
            final MethodHandle typedGetter = linkerServices.asType(boundGetter, type.changeReturnType(
                    MethodHandle.class));

            // Handle to invoke the setter R(MethodHandle, O, V)
            final MethodHandle invokeHandle = MethodHandles.exactInvoker(setterType);
            // Handle to invoke the setter, dropping unnecessary fold arguments R(MethodHandle, O, N, V)
            final MethodHandle invokeHandleFolded = MethodHandles.dropArguments(invokeHandle, 2, type.parameterType(
                    1));
            final GuardedInvocationComponent nextComponent = getGuardedInvocationComponent(callSiteDescriptor,
                    linkerServices, operations);

            final MethodHandle fallbackFolded;
            if(nextComponent == null) {
                // Object(MethodHandle)->Object(MethodHandle, O, N, V); returns constant null
                fallbackFolded = MethodHandles.dropArguments(CONSTANT_NULL_DROP_METHOD_HANDLE, 1,
                        type.parameterList()).asType(type.insertParameterTypes(0, MethodHandle.class));
            } else {
                // Object(O, N, V)->Object(MethodHandle, O, N, V); adapts the next component's invocation to drop the
                // extra argument resulting from fold
                fallbackFolded = MethodHandles.dropArguments(nextComponent.getGuardedInvocation().getInvocation(),
                        0, MethodHandle.class);
            }

            // fold(R(MethodHandle, O, N, V), MethodHandle(O, N, V))
            final MethodHandle compositeSetter = MethodHandles.foldArguments(MethodHandles.guardWithTest(
                        IS_METHOD_HANDLE_NOT_NULL, invokeHandleFolded, fallbackFolded), typedGetter);
            if(nextComponent == null) {
                return getClassGuardedInvocationComponent(compositeSetter, type);
            }
            return nextComponent.compose(compositeSetter, getClassGuard(type), clazz, ValidationType.EXACT_CLASS);
        }
        case 3: {
            // Must have two arguments: target object and property value
            assertParameterCount(callSiteDescriptor, 2);
            final GuardedInvocation gi = createGuardedDynamicMethodInvocation(callSiteDescriptor, linkerServices,
                    callSiteDescriptor.getNameToken(CallSiteDescriptor.NAME_OPERAND), propertySetters);
            // If we have a property setter with this name, this composite operation will always stop here
            if(gi != null) {
                return new GuardedInvocationComponent(gi, clazz, ValidationType.EXACT_CLASS);
            }
            // If we don't have a property setter with this name, always fall back to the next operation in the
            // composite (if any)
            return getGuardedInvocationComponent(callSiteDescriptor, linkerServices, operations);
        }
        default: {
            // More than two name components; don't know what to do with it.
            return null;
        }
    }
}