jdk/test/jdk/modules/etc/VerifyModuleDelegation.java

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/**
 * @test
 * @summary Verify the defining class loader of each module never delegates
 *          to its child class loader.
 * @run testng/othervm --add-modules=ALL-SYSTEM VerifyModuleDelegation
 */

import java.lang.module.ModuleDescriptor;
import java.lang.module.ModuleFinder;
import java.lang.module.ModuleReference;
import java.lang.reflect.Layer;
import java.lang.reflect.Module;
import java.util.Set;
import static java.util.stream.Collectors.toSet;

import static java.lang.module.ModuleDescriptor.Requires.Modifier.*;

import org.testng.annotations.*;

import static org.testng.Assert.*;

public class VerifyModuleDelegation {
    private static final String JAVA_BASE = "java.base";

    private static final ModuleDescriptor BASE
        = ModuleDescriptor.module(JAVA_BASE).build();

    private static final Set<ModuleDescriptor> MREFS
            = Layer.boot().modules().stream().map(Module::getDescriptor)
                .collect(toSet());

    private void check(ModuleDescriptor md, ModuleDescriptor ref) {
        assertTrue(md.requires().size() == ref.requires().size());
        assertTrue(md.requires().containsAll(ref.requires()));
    }

    @Test
    public void checkJavaBase() {
        ModuleDescriptor md =
                MREFS.stream()
                     .filter(d -> d.name().equals(JAVA_BASE))
                     .findFirst().orElseThrow(Error::new);

        check(md, BASE);
    }

    @Test
    public void checkLoaderDelegation() {
        Layer boot = Layer.boot();
        MREFS.stream()
             .forEach(md -> md.requires().stream().forEach(req ->
                 {
                     // check if M requires D and D's loader must be either the
                     // same or an ancestor of M's loader
                     ClassLoader loader1 = boot.findLoader(md.name());
                     ClassLoader loader2 = boot.findLoader(req.name());
                     if (loader1 != loader2 && !isAncestor(loader2, loader1)) {
                         throw new Error(md.name() + " can't delegate to " +
                                         "find classes from " + req.name());
                     }
                 }));
    }

    // Returns true if p is an ancestor of cl i.e. class loader 'p' can
    // be found in the cl's delegation chain
    private static boolean isAncestor(ClassLoader p, ClassLoader cl) {
        if (p != null && cl == null) {
            return false;
        }
        ClassLoader acl = cl;
        do {
            acl = acl.getParent();
            if (p == acl) {
                return true;
            }
        } while (acl != null);
        return false;
    }
}