It could be shown (see below a rewritten test case) that method handles for 254-ary methods claim less memory in Java 17 than in Java 11, when compiled and run by its tools.
Since no method-handle- or reflection-related features are advertised in release summaries for Java versions from 11 to 17, I'm curious: what changes have contributed to less memory consumption?
This is a rewritten test case ArityLimits.java:
import java.lang.invoke.MethodHandle;import java.lang.invoke.MethodHandles.Lookup;import java.lang.invoke.MethodHandles;import java.lang.reflect.Method;import java.lang.reflect.Modifier;import java.util.Collections;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.function.Consumer;import java.util.function.Supplier;class ArityLimits{ public static void main(String[] args) throws Throwable { // Pick an implementation with the 1st argument, e.g. core. final Invocable invocable = (args.length > 0&& args[0].equalsIgnoreCase("core")) ? new CoreInvoker(ArityLimits::new) : new HandleInvoker(ArityLimits::new, MethodHandles.privateLookupIn( ArityLimits.class, MethodHandles.lookup())); // Pick which methods to call with the 2nd argument, e.g. // $(( 1|2|4|8 )). final int agenda = (args.length > 1) ? 0xf & Integer.parseInt(args[1]) : (1 | 2 | 4 | 8); final Map<String, List<?>> arguments = new HashMap<>(8); if ((agenda & 1) != 0) arguments.put("passCrunchLongsFix128", Collections.nCopies(128 - 2 /* (handle, this) */, 0L)); if ((agenda & 2) != 0) arguments.put("passClassCrunchLongsFix128", Collections.nCopies(128 - 1 /* (handle) */, 0L)); if ((agenda & 4) != 0) arguments.put("passCrunchIntsFix255", Collections.nCopies(255 - 2 /* (handle, this) */, 0)); if ((agenda & 8) != 0) arguments.put("passClassCrunchIntsFix255", Collections.nCopies(255 - 1 /* (handle) */, 0)); final Consumer<Method> announcer = ("Linux".equalsIgnoreCase( System.getProperty("os.name", ""))) ? method -> System.err.format("\033[7m%s\033[0m%n", method.getName()) : method -> System.err.println(method.getName()); for (Method method : ArityLimits.class.getDeclaredMethods()) { final List<?> methodArgs = arguments.get( method.getName()); if (methodArgs == null) continue; invocable.invoke(method, methodArgs); announcer.accept(method); } } private interface Invocable { void invoke(Method method, List<?> args) throws Throwable; static boolean warnTooManyArgs(Method method, List<?> args) { if (method.isVarArgs() || args.size() < 256) return false; System.err.println(method.getName() .concat(": too many arguments")); return true; } } private static final class CoreInvoker implements Invocable { private final Supplier<?> instanceer; CoreInvoker(Supplier<?> instanceer) { this.instanceer = instanceer; } public void invoke(Method method, List<?> args) throws ReflectiveOperationException { if (Invocable.warnTooManyArgs(method, args)) return; method.invoke((Modifier.isStatic(method.getModifiers())) ? null : instanceer.get(), args.toArray()); } } private static final class HandleInvoker implements Invocable { private final Supplier<?> instanceer; private final Lookup lookup; HandleInvoker(Supplier<?> instanceer, Lookup lookup) { this.instanceer = instanceer; this.lookup = lookup; } public void invoke(Method method, List<?> args) throws Throwable { // Here a handle shall check its parameter constraints. final MethodHandle mh1 = lookup.unreflect(method); if (Invocable.warnTooManyArgs(method, args)) return; final MethodHandle mh2 = (Modifier.isStatic( method.getModifiers())) ? mh1 : mh1.bindTo(instanceer.get()); mh2.invokeWithArguments(args); } } void passCrunchLongsFix128(/* MethodHandle mh, ArityLimits al, */ long _001, long _002, long _003, long _004, long _005, long _006, long _007, long _008, long _009, long _010, long _011, long _012, long _013, long _014, long _015, long _016, long _017, long _018, long _019, long _020, long _021, long _022, long _023, long _024, long _025, long _026, long _027, long _028, long _029, long _030, long _031, long _032, long _033, long _034, long _035, long _036, long _037, long _038, long _039, long _040, long _041, long _042, long _043, long _044, long _045, long _046, long _047, long _048, long _049, long _050, long _051, long _052, long _053, long _054, long _055, long _056, long _057, long _058, long _059, long _060, long _061, long _062, long _063, long _064, long _065, long _066, long _067, long _068, long _069, long _070, long _071, long _072, long _073, long _074, long _075, long _076, long _077, long _078, long _079, long _080, long _081, long _082, long _083, long _084, long _085, long _086, long _087, long _088, long _089, long _090, long _091, long _092, long _093, long _094, long _095, long _096, long _097, long _098, long _099, long _100, long _101, long _102, long _103, long _104, long _105, long _106, long _107, long _108, long _109, long _110, long _111, long _112, long _113, long _114, long _115, long _116, long _117, long _118, long _119, long _120, long _121, long _122, long _123, long _124, long _125, long _126) { } static void passClassCrunchLongsFix128(/* MethodHandle mh, */ long _001, long _002, long _003, long _004, long _005, long _006, long _007, long _008, long _009, long _010, long _011, long _012, long _013, long _014, long _015, long _016, long _017, long _018, long _019, long _020, long _021, long _022, long _023, long _024, long _025, long _026, long _027, long _028, long _029, long _030, long _031, long _032, long _033, long _034, long _035, long _036, long _037, long _038, long _039, long _040, long _041, long _042, long _043, long _044, long _045, long _046, long _047, long _048, long _049, long _050, long _051, long _052, long _053, long _054, long _055, long _056, long _057, long _058, long _059, long _060, long _061, long _062, long _063, long _064, long _065, long _066, long _067, long _068, long _069, long _070, long _071, long _072, long _073, long _074, long _075, long _076, long _077, long _078, long _079, long _080, long _081, long _082, long _083, long _084, long _085, long _086, long _087, long _088, long _089, long _090, long _091, long _092, long _093, long _094, long _095, long _096, long _097, long _098, long _099, long _100, long _101, long _102, long _103, long _104, long _105, long _106, long _107, long _108, long _109, long _110, long _111, long _112, long _113, long _114, long _115, long _116, long _117, long _118, long _119, long _120, long _121, long _122, long _123, long _124, long _125, long _126, long _127) { } void passCrunchIntsFix255(/* MethodHandle mh, ArityLimits al, */ int _001, int _002, int _003, int _004, int _005, int _006, int _007, int _008, int _009, int _010, int _011, int _012, int _013, int _014, int _015, int _016, int _017, int _018, int _019, int _020, int _021, int _022, int _023, int _024, int _025, int _026, int _027, int _028, int _029, int _030, int _031, int _032, int _033, int _034, int _035, int _036, int _037, int _038, int _039, int _040, int _041, int _042, int _043, int _044, int _045, int _046, int _047, int _048, int _049, int _050, int _051, int _052, int _053, int _054, int _055, int _056, int _057, int _058, int _059, int _060, int _061, int _062, int _063, int _064, int _065, int _066, int _067, int _068, int _069, int _070, int _071, int _072, int _073, int _074, int _075, int _076, int _077, int _078, int _079, int _080, int _081, int _082, int _083, int _084, int _085, int _086, int _087, int _088, int _089, int _090, int _091, int _092, int _093, int _094, int _095, int _096, int _097, int _098, int _099, int _100, int _101, int _102, int _103, int _104, int _105, int _106, int _107, int _108, int _109, int _110, int _111, int _112, int _113, int _114, int _115, int _116, int _117, int _118, int _119, int _120, int _121, int _122, int _123, int _124, int _125, int _126, int _127, int _128, int _129, int _130, int _131, int _132, int _133, int _134, int _135, int _136, int _137, int _138, int _139, int _140, int _141, int _142, int _143, int _144, int _145, int _146, int _147, int _148, int _149, int _150, int _151, int _152, int _153, int _154, int _155, int _156, int _157, int _158, int _159, int _160, int _161, int _162, int _163, int _164, int _165, int _166, int _167, int _168, int _169, int _170, int _171, int _172, int _173, int _174, int _175, int _176, int _177, int _178, int _179, int _180, int _181, int _182, int _183, int _184, int _185, int _186, int _187, int _188, int _189, int _190, int _191, int _192, int _193, int _194, int _195, int _196, int _197, int _198, int _199, int _200, int _201, int _202, int _203, int _204, int _205, int _206, int _207, int _208, int _209, int _210, int _211, int _212, int _213, int _214, int _215, int _216, int _217, int _218, int _219, int _220, int _221, int _222, int _223, int _224, int _225, int _226, int _227, int _228, int _229, int _230, int _231, int _232, int _233, int _234, int _235, int _236, int _237, int _238, int _239, int _240, int _241, int _242, int _243, int _244, int _245, int _246, int _247, int _248, int _249, int _250, int _251, int _252, int _253) { } static void passClassCrunchIntsFix255(/* MethodHandle mh, */ int _001, int _002, int _003, int _004, int _005, int _006, int _007, int _008, int _009, int _010, int _011, int _012, int _013, int _014, int _015, int _016, int _017, int _018, int _019, int _020, int _021, int _022, int _023, int _024, int _025, int _026, int _027, int _028, int _029, int _030, int _031, int _032, int _033, int _034, int _035, int _036, int _037, int _038, int _039, int _040, int _041, int _042, int _043, int _044, int _045, int _046, int _047, int _048, int _049, int _050, int _051, int _052, int _053, int _054, int _055, int _056, int _057, int _058, int _059, int _060, int _061, int _062, int _063, int _064, int _065, int _066, int _067, int _068, int _069, int _070, int _071, int _072, int _073, int _074, int _075, int _076, int _077, int _078, int _079, int _080, int _081, int _082, int _083, int _084, int _085, int _086, int _087, int _088, int _089, int _090, int _091, int _092, int _093, int _094, int _095, int _096, int _097, int _098, int _099, int _100, int _101, int _102, int _103, int _104, int _105, int _106, int _107, int _108, int _109, int _110, int _111, int _112, int _113, int _114, int _115, int _116, int _117, int _118, int _119, int _120, int _121, int _122, int _123, int _124, int _125, int _126, int _127, int _128, int _129, int _130, int _131, int _132, int _133, int _134, int _135, int _136, int _137, int _138, int _139, int _140, int _141, int _142, int _143, int _144, int _145, int _146, int _147, int _148, int _149, int _150, int _151, int _152, int _153, int _154, int _155, int _156, int _157, int _158, int _159, int _160, int _161, int _162, int _163, int _164, int _165, int _166, int _167, int _168, int _169, int _170, int _171, int _172, int _173, int _174, int _175, int _176, int _177, int _178, int _179, int _180, int _181, int _182, int _183, int _184, int _185, int _186, int _187, int _188, int _189, int _190, int _191, int _192, int _193, int _194, int _195, int _196, int _197, int _198, int _199, int _200, int _201, int _202, int _203, int _204, int _205, int _206, int _207, int _208, int _209, int _210, int _211, int _212, int _213, int _214, int _215, int _216, int _217, int _218, int _219, int _220, int _221, int _222, int _223, int _224, int _225, int _226, int _227, int _228, int _229, int _230, int _231, int _232, int _233, int _234, int _235, int _236, int _237, int _238, int _239, int _240, int _241, int _242, int _243, int _244, int _245, int _246, int _247, int _248, int _249, int _250, int _251, int _252, int _253, int _254) { }}This is an argument file args:
-XX:+UnlockExperimentalVMOptions-XX:+UseEpsilonGC-XX:+AlwaysPreTouch-Xms136m-Xmx136m-Xlog:heap*=info,gc=infoSave the files in, for example, a /tmp directory, and start a Java 11 version Docker container:
docker run --entrypoint /bin/sh --interactive \ --rm --tty --volume="/tmp:/tmp" \ --workdir="/tmp" eclipse-temurin:11-jdk-alpine # It may pull in ~200 MiB.javac -Xdiags:verbose -Xlint ArityLimits.javajava @args ArityLimits handle $(( 1 | 2 | 4 | 8 )) # 91/136 MiB of heap usedjava @args ArityLimits handle 8 # 36/136 (see title)java @args ArityLimits core $(( 1 | 2 | 4 | 8 )) # 1/136java @args ArityLimits core 8 # 1/136rm *.classexitNow, start a Java 17 version Docker container:
docker run --entrypoint /bin/sh --interactive \ --rm --tty --volume="/tmp:/tmp" \ --workdir="/tmp" eclipse-temurin:17-jdk-alpine # It may pull in ~200 MiB.javac -Xdiags:verbose -Xlint ArityLimits.javajava @args ArityLimits handle $(( 1 | 2 | 4 | 8 )) # 5/136 MiB of heap usedjava @args ArityLimits handle 8 # 3/136 (see title)java @args ArityLimits core $(( 1 | 2 | 4 | 8 )) # 1/136java @args ArityLimits core 8 # 1/136rm *.classexit