Java example source code file (MethodTypeForm.java)

This example Java source code file (MethodTypeForm.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

class, dmh, erase, ints, jvm, lambdaform, methodhandle, methodtype, methodtypeform, raw_return, stable, string, wrapper

The MethodTypeForm.java Java example source code

/*
 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang.invoke;

import sun.invoke.util.Wrapper;
import static java.lang.invoke.MethodHandleStatics.*;
import static java.lang.invoke.MethodHandleNatives.Constants.*;
 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;

/**
 * Shared information for a group of method types, which differ
 * only by reference types, and therefore share a common erasure
 * and wrapping.
 * <p>
 * For an empirical discussion of the structure of method types,
 * see <a href="http://groups.google.com/group/jvm-languages/browse_thread/thread/ac9308ae74da9b7e/">
 * the thread "Avoiding Boxing" on jvm-languages</a>.
 * There are approximately 2000 distinct erased method types in the JDK.
 * There are a little over 10 times that number of unerased types.
 * No more than half of these are likely to be loaded at once.
 * @author John Rose
 */
final class MethodTypeForm {
    final int[] argToSlotTable, slotToArgTable;
    final long argCounts;               // packed slot & value counts
    final long primCounts;              // packed prim & double counts
    final int vmslots;                  // total number of parameter slots
    final MethodType erasedType;        // the canonical erasure
    final MethodType basicType;         // the canonical erasure, with primitives simplified

    // Cached adapter information:
    @Stable String typeString;           // argument type signature characters
    @Stable MethodHandle genericInvoker; // JVM hook for inexact invoke
    @Stable MethodHandle basicInvoker;   // cached instance of MH.invokeBasic
    @Stable MethodHandle namedFunctionInvoker; // cached helper for LF.NamedFunction

    // Cached lambda form information, for basic types only:
    final @Stable LambdaForm[] lambdaForms;
    // Indexes into lambdaForms:
    static final int
            LF_INVVIRTUAL     =  0,  // DMH invokeVirtual
            LF_INVSTATIC      =  1,
            LF_INVSPECIAL     =  2,
            LF_NEWINVSPECIAL  =  3,
            LF_INVINTERFACE   =  4,
            LF_INVSTATIC_INIT =  5,  // DMH invokeStatic with <clinit> barrier
            LF_INTERPRET      =  6,  // LF interpreter
            LF_COUNTER        =  7,  // CMH wrapper
            LF_REINVOKE       =  8,  // other wrapper
            LF_EX_LINKER      =  9,  // invokeExact_MT
            LF_EX_INVOKER     = 10,  // invokeExact MH
            LF_GEN_LINKER     = 11,
            LF_GEN_INVOKER    = 12,
            LF_CS_LINKER      = 13,  // linkToCallSite_CS
            LF_MH_LINKER      = 14,  // linkToCallSite_MH
            LF_LIMIT          = 15;

    public MethodType erasedType() {
        return erasedType;
    }

    public MethodType basicType() {
        return basicType;
    }

    public LambdaForm cachedLambdaForm(int which) {
        return lambdaForms[which];
    }

    public LambdaForm setCachedLambdaForm(int which, LambdaForm form) {
        // Should we perform some sort of CAS, to avoid racy duplication?
        return lambdaForms[which] = form;
    }

    public MethodHandle basicInvoker() {
        assert(erasedType == basicType) : "erasedType: " + erasedType + " != basicType: " + basicType;  // primitives must be flattened also
        MethodHandle invoker = basicInvoker;
        if (invoker != null)  return invoker;
        invoker = DirectMethodHandle.make(invokeBasicMethod(basicType));
        basicInvoker = invoker;
        return invoker;
    }

    // This next one is called from LambdaForm.NamedFunction.<init>.
    /*non-public*/ static MemberName invokeBasicMethod(MethodType basicType) {
        assert(basicType == basicType.basicType());
        try {
            // Do approximately the same as this public API call:
            //   Lookup.findVirtual(MethodHandle.class, name, type);
            // But bypass access and corner case checks, since we know exactly what we need.
            return IMPL_LOOKUP.resolveOrFail(REF_invokeVirtual, MethodHandle.class, "invokeBasic", basicType);
         } catch (ReflectiveOperationException ex) {
            throw newInternalError("JVM cannot find invoker for "+basicType, ex);
        }
    }

    /**
     * Build an MTF for a given type, which must have all references erased to Object.
     * This MTF will stand for that type and all un-erased variations.
     * Eagerly compute some basic properties of the type, common to all variations.
     */
    protected MethodTypeForm(MethodType erasedType) {
        this.erasedType = erasedType;

        Class<?>[] ptypes = erasedType.ptypes();
        int ptypeCount = ptypes.length;
        int pslotCount = ptypeCount;            // temp. estimate
        int rtypeCount = 1;                     // temp. estimate
        int rslotCount = 1;                     // temp. estimate

        int[] argToSlotTab = null, slotToArgTab = null;

        // Walk the argument types, looking for primitives.
        int pac = 0, lac = 0, prc = 0, lrc = 0;
        Class<?>[] epts = ptypes;
        Class<?>[] bpts = epts;
        for (int i = 0; i < epts.length; i++) {
            Class<?> pt = epts[i];
            if (pt != Object.class) {
                ++pac;
                Wrapper w = Wrapper.forPrimitiveType(pt);
                if (w.isDoubleWord())  ++lac;
                if (w.isSubwordOrInt() && pt != int.class) {
                    if (bpts == epts)
                        bpts = bpts.clone();
                    bpts[i] = int.class;
                }
            }
        }
        pslotCount += lac;                  // #slots = #args + #longs
        Class<?> rt = erasedType.returnType();
        Class<?> bt = rt;
        if (rt != Object.class) {
            ++prc;          // even void.class counts as a prim here
            Wrapper w = Wrapper.forPrimitiveType(rt);
            if (w.isDoubleWord())  ++lrc;
            if (w.isSubwordOrInt() && rt != int.class)
                bt = int.class;
            // adjust #slots, #args
            if (rt == void.class)
                rtypeCount = rslotCount = 0;
            else
                rslotCount += lrc;
        }
        if (epts == bpts && bt == rt) {
            this.basicType = erasedType;
        } else {
            this.basicType = MethodType.makeImpl(bt, bpts, true);
        }
        if (lac != 0) {
            int slot = ptypeCount + lac;
            slotToArgTab = new int[slot+1];
            argToSlotTab = new int[1+ptypeCount];
            argToSlotTab[0] = slot;  // argument "-1" is past end of slots
            for (int i = 0; i < epts.length; i++) {
                Class<?> pt = epts[i];
                Wrapper w = Wrapper.forBasicType(pt);
                if (w.isDoubleWord())  --slot;
                --slot;
                slotToArgTab[slot] = i+1; // "+1" see argSlotToParameter note
                argToSlotTab[1+i]  = slot;
            }
            assert(slot == 0);  // filled the table
        }
        this.primCounts = pack(lrc, prc, lac, pac);
        this.argCounts = pack(rslotCount, rtypeCount, pslotCount, ptypeCount);
        if (slotToArgTab == null) {
            int slot = ptypeCount; // first arg is deepest in stack
            slotToArgTab = new int[slot+1];
            argToSlotTab = new int[1+ptypeCount];
            argToSlotTab[0] = slot;  // argument "-1" is past end of slots
            for (int i = 0; i < ptypeCount; i++) {
                --slot;
                slotToArgTab[slot] = i+1; // "+1" see argSlotToParameter note
                argToSlotTab[1+i]  = slot;
            }
        }
        this.argToSlotTable = argToSlotTab;
        this.slotToArgTable = slotToArgTab;

        if (pslotCount >= 256)  throw newIllegalArgumentException("too many arguments");

        // send a few bits down to the JVM:
        this.vmslots = parameterSlotCount();

        if (basicType == erasedType) {
            lambdaForms = new LambdaForm[LF_LIMIT];
        } else {
            lambdaForms = null;  // could be basicType.form().lambdaForms;
        }
    }

    private static long pack(int a, int b, int c, int d) {
        assert(((a|b|c|d) & ~0xFFFF) == 0);
        long hw = ((a << 16) | b), lw = ((c << 16) | d);
        return (hw << 32) | lw;
    }
    private static char unpack(long packed, int word) { // word==0 => return a, ==3 => return d
        assert(word <= 3);
        return (char)(packed >> ((3-word) * 16));
    }

    public int parameterCount() {                      // # outgoing values
        return unpack(argCounts, 3);
    }
    public int parameterSlotCount() {                  // # outgoing interpreter slots
        return unpack(argCounts, 2);
    }
    public int returnCount() {                         // = 0 (V), or 1
        return unpack(argCounts, 1);
    }
    public int returnSlotCount() {                     // = 0 (V), 2 (J/D), or 1
        return unpack(argCounts, 0);
    }
    public int primitiveParameterCount() {
        return unpack(primCounts, 3);
    }
    public int longPrimitiveParameterCount() {
        return unpack(primCounts, 2);
    }
    public int primitiveReturnCount() {                // = 0 (obj), or 1
        return unpack(primCounts, 1);
    }
    public int longPrimitiveReturnCount() {            // = 1 (J/D), or 0
        return unpack(primCounts, 0);
    }
    public boolean hasPrimitives() {
        return primCounts != 0;
    }
    public boolean hasNonVoidPrimitives() {
        if (primCounts == 0)  return false;
        if (primitiveParameterCount() != 0)  return true;
        return (primitiveReturnCount() != 0 && returnCount() != 0);
    }
    public boolean hasLongPrimitives() {
        return (longPrimitiveParameterCount() | longPrimitiveReturnCount()) != 0;
    }
    public int parameterToArgSlot(int i) {
        return argToSlotTable[1+i];
    }
    public int argSlotToParameter(int argSlot) {
        // Note:  Empty slots are represented by zero in this table.
        // Valid arguments slots contain incremented entries, so as to be non-zero.
        // We return -1 the caller to mean an empty slot.
        return slotToArgTable[argSlot] - 1;
    }

    static MethodTypeForm findForm(MethodType mt) {
        MethodType erased = canonicalize(mt, ERASE, ERASE);
        if (erased == null) {
            // It is already erased.  Make a new MethodTypeForm.
            return new MethodTypeForm(mt);
        } else {
            // Share the MethodTypeForm with the erased version.
            return erased.form();
        }
    }

    /** Codes for {@link #canonicalize(java.lang.Class, int)}.
     * ERASE means change every reference to {@code Object}.
     * WRAP means convert primitives (including {@code void} to their
     * corresponding wrapper types.  UNWRAP means the reverse of WRAP.
     * INTS means convert all non-void primitive types to int or long,
     * according to size.  LONGS means convert all non-void primitives
     * to long, regardless of size.  RAW_RETURN means convert a type
     * (assumed to be a return type) to int if it is smaller than an int,
     * or if it is void.
     */
    public static final int NO_CHANGE = 0, ERASE = 1, WRAP = 2, UNWRAP = 3, INTS = 4, LONGS = 5, RAW_RETURN = 6;

    /** Canonicalize the types in the given method type.
     * If any types change, intern the new type, and return it.
     * Otherwise return null.
     */
    public static MethodType canonicalize(MethodType mt, int howRet, int howArgs) {
        Class<?>[] ptypes = mt.ptypes();
        Class<?>[] ptc = MethodTypeForm.canonicalizes(ptypes, howArgs);
        Class<?> rtype = mt.returnType();
        Class<?> rtc = MethodTypeForm.canonicalize(rtype, howRet);
        if (ptc == null && rtc == null) {
            // It is already canonical.
            return null;
        }
        // Find the erased version of the method type:
        if (rtc == null)  rtc = rtype;
        if (ptc == null)  ptc = ptypes;
        return MethodType.makeImpl(rtc, ptc, true);
    }

    /** Canonicalize the given return or param type.
     *  Return null if the type is already canonicalized.
     */
    static Class<?> canonicalize(Class t, int how) {
        Class<?> ct;
        if (t == Object.class) {
            // no change, ever
        } else if (!t.isPrimitive()) {
            switch (how) {
                case UNWRAP:
                    ct = Wrapper.asPrimitiveType(t);
                    if (ct != t)  return ct;
                    break;
                case RAW_RETURN:
                case ERASE:
                    return Object.class;
            }
        } else if (t == void.class) {
            // no change, usually
            switch (how) {
                case RAW_RETURN:
                    return int.class;
                case WRAP:
                    return Void.class;
            }
        } else {
            // non-void primitive
            switch (how) {
                case WRAP:
                    return Wrapper.asWrapperType(t);
                case INTS:
                    if (t == int.class || t == long.class)
                        return null;  // no change
                    if (t == double.class)
                        return long.class;
                    return int.class;
                case LONGS:
                    if (t == long.class)
                        return null;  // no change
                    return long.class;
                case RAW_RETURN:
                    if (t == int.class || t == long.class ||
                        t == float.class || t == double.class)
                        return null;  // no change
                    // everything else returns as an int
                    return int.class;
            }
        }
        // no change; return null to signify
        return null;
    }

    /** Canonicalize each param type in the given array.
     *  Return null if all types are already canonicalized.
     */
    static Class<?>[] canonicalizes(Class[] ts, int how) {
        Class<?>[] cs = null;
        for (int imax = ts.length, i = 0; i < imax; i++) {
            Class<?> c = canonicalize(ts[i], how);
            if (c == void.class)
                c = null;  // a Void parameter was unwrapped to void; ignore
            if (c != null) {
                if (cs == null)
                    cs = ts.clone();
                cs[i] = c;
            }
        }
        return cs;
    }

    @Override
    public String toString() {
        return "Form"+erasedType;
    }

}