/*

 * Copyright (c) 2014, 2017, 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;

import java.io.IOException;

import java.io.InputStream;

import java.lang.annotation.Annotation;

import java.lang.module.Configuration;

import java.lang.module.ModuleReference;

import java.lang.module.ModuleDescriptor;

import java.lang.module.ModuleDescriptor.Exports;

import java.lang.module.ModuleDescriptor.Opens;

import java.lang.module.ModuleDescriptor.Version;

import java.lang.module.ResolvedModule;

import java.lang.reflect.AnnotatedElement;

import java.net.URI;

import java.net.URL;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Collections;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.Optional;

import java.util.Set;

import java.util.concurrent.ConcurrentHashMap;

import java.util.function.Function;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import jdk.internal.loader.BuiltinClassLoader;

import jdk.internal.loader.BootLoader;

import jdk.internal.loader.ClassLoaders;

import jdk.internal.module.IllegalAccessLogger;

import jdk.internal.module.ModuleLoaderMap;

import jdk.internal.module.ServicesCatalog;

import jdk.internal.module.Resources;

import jdk.internal.org.objectweb.asm.AnnotationVisitor;

import jdk.internal.org.objectweb.asm.Attribute;

import jdk.internal.org.objectweb.asm.ClassReader;

import jdk.internal.org.objectweb.asm.ClassVisitor;

import jdk.internal.org.objectweb.asm.ClassWriter;

import jdk.internal.org.objectweb.asm.ModuleVisitor;

import jdk.internal.org.objectweb.asm.Opcodes;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import sun.security.util.SecurityConstants;

/**

 * Represents a run-time module, either {@link #isNamed() named} or unnamed.

 *

 * <p> Named modules have a {@link #getName() name} and are constructed by the

 * Java Virtual Machine when a graph of modules is defined to the Java virtual

 * machine to create a {@linkplain ModuleLayer module layer}. </p>

 *

 * <p> An unnamed module does not have a name. There is an unnamed module for

 * each {@link ClassLoader ClassLoader}, obtained by invoking its {@link

 * ClassLoader#getUnnamedModule() getUnnamedModule} method. All types that are

 * not in a named module are members of their defining class loader's unnamed

 * module. </p>

 *

 * <p> The package names that are parameters or returned by methods defined in

 * this class are the fully-qualified names of the packages as defined in

 * section 6.5.3 of <cite>The Java&trade; Language Specification</cite>, for

 * example, {@code "java.lang"}. </p>

 *

 * <p> Unless otherwise specified, passing a {@code null} argument to a method

 * in this class causes a {@link NullPointerException NullPointerException} to

 * be thrown. </p>

 *

 * @since 9

 * @spec JPMS

 * @see Class#getModule()

 */

public final class Module implements AnnotatedElement {

    // the layer that contains this module, can be null

    private final ModuleLayer layer;

    // module name and loader, these fields are read by VM

    private final String name;

    private final ClassLoader loader;

    // the module descriptor

    private final ModuleDescriptor descriptor;

    /**

     * Creates a new named Module. The resulting Module will be defined to the

     * VM but will not read any other modules, will not have any exports setup

     * and will not be registered in the service catalog.

     */

    Module(ModuleLayer layer,

           ClassLoader loader,

           ModuleDescriptor descriptor,

           URI uri)

    {

        this.layer = layer;

        this.name = descriptor.name();

        this.loader = loader;

        this.descriptor = descriptor;

        // define module to VM

        boolean isOpen = descriptor.isOpen() || descriptor.isAutomatic();

        Version version = descriptor.version().orElse(null);

        String vs = Objects.toString(version, null);

        String loc = Objects.toString(uri, null);

        String[] packages = descriptor.packages().toArray(new String[0]);

        defineModule0(this, isOpen, vs, loc, packages);

    }

    /**

     * Create the unnamed Module for the given ClassLoader.

     *

     * @see ClassLoader#getUnnamedModule

     */

    Module(ClassLoader loader) {

        this.layer = null;

        this.name = null;

        this.loader = loader;

        this.descriptor = null;

    }

    /**

     * Creates a named module but without defining the module to the VM.

     *

     * @apiNote This constructor is for VM white-box testing.

     */

    Module(ClassLoader loader, ModuleDescriptor descriptor) {

        this.layer = null;

        this.name = descriptor.name();

        this.loader = loader;

        this.descriptor = descriptor;

    }

    /**

     * Returns {@code true} if this module is a named module.

     *

     * @return {@code true} if this is a named module

     *

     * @see ClassLoader#getUnnamedModule()

     */

    public boolean isNamed() {

        return name != null;

    }

    /**

     * Returns the module name or {@code null} if this module is an unnamed

     * module.

     *

     * @return The module name

     */

    public String getName() {

        return name;

    }

    /**

     * Returns the {@code ClassLoader} for this module.

     *

     * <p> If there is a security manager then its {@code checkPermission}

     * method if first called with a {@code RuntimePermission("getClassLoader")}

     * permission to check that the caller is allowed to get access to the

     * class loader. </p>

     *

     * @return The class loader for this module

     *

     * @throws SecurityException

     *         If denied by the security manager

     */

    public ClassLoader getClassLoader() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

        }

        return loader;

    }

    /**

     * Returns the module descriptor for this module or {@code null} if this

     * module is an unnamed module.

     *

     * @return The module descriptor for this module

     */

    public ModuleDescriptor getDescriptor() {

        return descriptor;

    }

    /**

     * Returns the module layer that contains this module or {@code null} if

     * this module is not in a module layer.

     *

     * A module layer contains named modules and therefore this method always

     * returns {@code null} when invoked on an unnamed module.

     *

     * <p> <a href="reflect/Proxy.html#dynamicmodule">Dynamic modules</a> are

     * named modules that are generated at runtime. A dynamic module may or may

     * not be in a module layer. </p>

     *

     * @return The module layer that contains this module

     *

     * @see java.lang.reflect.Proxy

     */

    public ModuleLayer getLayer() {

        if (isNamed()) {

            ModuleLayer layer = this.layer;

            if (layer != null)

                return layer;

            // special-case java.base as it is created before the boot layer

            if (loader == null && name.equals("java.base")) {

                return ModuleLayer.boot();

            }

        }

        return null;

    }

    // --

    // special Module to mean "all unnamed modules"

    private static final Module ALL_UNNAMED_MODULE = new Module(null);

    private static final Set<Module> ALL_UNNAMED_MODULE_SET = Set.of(ALL_UNNAMED_MODULE);

    // special Module to mean "everyone"

    private static final Module EVERYONE_MODULE = new Module(null);

    private static final Set<Module> EVERYONE_SET = Set.of(EVERYONE_MODULE);

    /**

     * The holder of data structures to support readability, exports, and

     * service use added at runtime with the reflective APIs.

     */

    private static class ReflectionData {

        /**

         * A module (1st key) reads another module (2nd key)

         */

        static final WeakPairMap<Module, Module, Boolean> reads =

            new WeakPairMap<>();

        /**

         * A module (1st key) exports or opens a package to another module

         * (2nd key). The map value is a map of package name to a boolean

         * that indicates if the package is opened.

         */

        static final WeakPairMap<Module, Module, Map<String, Boolean>> exports =

            new WeakPairMap<>();

        /**

         * A module (1st key) uses a service (2nd key)

         */

        static final WeakPairMap<Module, Class<?>, Boolean> uses =

            new WeakPairMap<>();

    }

    // -- readability --

    // the modules that this module reads

    private volatile Set<Module> reads;

    /**

     * Indicates if this module reads the given module. This method returns

     * {@code true} if invoked to test if this module reads itself. It also

     * returns {@code true} if invoked on an unnamed module (as unnamed

     * modules read all modules).

     *

     * @param  other

     *         The other module

     *

     * @return {@code true} if this module reads {@code other}

     *

     * @see #addReads(Module)

     */

    public boolean canRead(Module other) {

        Objects.requireNonNull(other);

        // an unnamed module reads all modules

        if (!this.isNamed())

            return true;

        // all modules read themselves

        if (other == this)

            return true;

        // check if this module reads other

        if (other.isNamed()) {

            Set<Module> reads = this.reads; // volatile read

            if (reads != null && reads.contains(other))

                return true;

        }

        // check if this module reads the other module reflectively

        if (ReflectionData.reads.containsKeyPair(this, other))

            return true;

        // if other is an unnamed module then check if this module reads

        // all unnamed modules

        if (!other.isNamed()

            && ReflectionData.reads.containsKeyPair(this, ALL_UNNAMED_MODULE))

            return true;

        return false;

    }

    /**

     * If the caller's module is this module then update this module to read

     * the given module.

     *

     * This method is a no-op if {@code other} is this module (all modules read

     * themselves), this module is an unnamed module (as unnamed modules read

     * all modules), or this module already reads {@code other}.

     *

     * @implNote <em>Read edges</em> added by this method are <em>weak</em> and

     * do not prevent {@code other} from being GC'ed when this module is

     * strongly reachable.

     *

     * @param  other

     *         The other module

     *

     * @return this module

     *

     * @throws IllegalCallerException

     *         If this is a named module and the caller's module is not this

     *         module

     *

     * @see #canRead

     */

    @CallerSensitive

    public Module addReads(Module other) {

        Objects.requireNonNull(other);

        if (this.isNamed()) {

            Module caller = getCallerModule(Reflection.getCallerClass());

            if (caller != this) {

                throw new IllegalCallerException(caller + " != " + this);

            }

            implAddReads(other, true);

        }

        return this;

    }

    /**

     * Updates this module to read another module.

     *

     * @apiNote Used by the --add-reads command line option.

     */

    void implAddReads(Module other) {

        implAddReads(other, true);

    }

    /**

     * Updates this module to read all unnamed modules.

     *

     * @apiNote Used by the --add-reads command line option.

     */

    void implAddReadsAllUnnamed() {

        implAddReads(Module.ALL_UNNAMED_MODULE, true);

    }

    /**

     * Updates this module to read another module without notifying the VM.

     *

     * @apiNote This method is for VM white-box testing.

     */

    void implAddReadsNoSync(Module other) {

        implAddReads(other, false);

    }

    /**

     * Makes the given {@code Module} readable to this module.

     *

     * If {@code syncVM} is {@code true} then the VM is notified.

     */

    private void implAddReads(Module other, boolean syncVM) {

        Objects.requireNonNull(other);

        if (!canRead(other)) {

            // update VM first, just in case it fails

            if (syncVM) {

                if (other == ALL_UNNAMED_MODULE) {

                    addReads0(this, null);

                } else {

                    addReads0(this, other);

                }

            }

            // add reflective read

            ReflectionData.reads.putIfAbsent(this, other, Boolean.TRUE);

        }

    }

    // -- exported and open packages --

    // the packages are open to other modules, can be null

    // if the value contains EVERYONE_MODULE then the package is open to all

    private volatile Map<String, Set<Module>> openPackages;

    // the packages that are exported, can be null

    // if the value contains EVERYONE_MODULE then the package is exported to all

    private volatile Map<String, Set<Module>> exportedPackages;

    /**

     * Returns {@code true} if this module exports the given package to at

     * least the given module.

     *

     * <p> This method returns {@code true} if invoked to test if a package in

     * this module is exported to itself. It always returns {@code true} when

     * invoked on an unnamed module. A package that is {@link #isOpen open} to

     * the given module is considered exported to that module at run-time and

     * so this method returns {@code true} if the package is open to the given

     * module. </p>

     *

     * <p> This method does not check if the given module reads this module. </p>

     *

     * @param  pn

     *         The package name

     * @param  other

     *         The other module

     *

     * @return {@code true} if this module exports the package to at least the

     *         given module

     *

     * @see ModuleDescriptor#exports()

     * @see #addExports(String,Module)

     */

    public boolean isExported(String pn, Module other) {

        Objects.requireNonNull(pn);

        Objects.requireNonNull(other);

        return implIsExportedOrOpen(pn, other, /*open*/false);

    }

    /**

     * Returns {@code true} if this module has <em>opened</em> a package to at

     * least the given module.

     *

     * <p> This method returns {@code true} if invoked to test if a package in

     * this module is open to itself. It returns {@code true} when invoked on an

     * {@link ModuleDescriptor#isOpen open} module with a package in the module.

     * It always returns {@code true} when invoked on an unnamed module. </p>

     *

     * <p> This method does not check if the given module reads this module. </p>

     *

     * @param  pn

     *         The package name

     * @param  other

     *         The other module

     *

     * @return {@code true} if this module has <em>opened</em> the package

     *         to at least the given module

     *

     * @see ModuleDescriptor#opens()

     * @see #addOpens(String,Module)

     * @see AccessibleObject#setAccessible(boolean)

     * @see java.lang.invoke.MethodHandles#privateLookupIn

     */

    public boolean isOpen(String pn, Module other) {

        Objects.requireNonNull(pn);

        Objects.requireNonNull(other);

        return implIsExportedOrOpen(pn, other, /*open*/true);

    }

    /**

     * Returns {@code true} if this module exports the given package

     * unconditionally.

     *

     * <p> This method always returns {@code true} when invoked on an unnamed

     * module. A package that is {@link #isOpen(String) opened} unconditionally

     * is considered exported unconditionally at run-time and so this method

     * returns {@code true} if the package is opened unconditionally. </p>

     *

     * <p> This method does not check if the given module reads this module. </p>

     *

     * @param  pn

     *         The package name

     *

     * @return {@code true} if this module exports the package unconditionally

     *

     * @see ModuleDescriptor#exports()

     */

    public boolean isExported(String pn) {

        Objects.requireNonNull(pn);

        return implIsExportedOrOpen(pn, EVERYONE_MODULE, /*open*/false);

    }

    /**

     * Returns {@code true} if this module has <em>opened</em> a package

     * unconditionally.

     *

     * <p> This method always returns {@code true} when invoked on an unnamed

     * module. Additionally, it always returns {@code true} when invoked on an

     * {@link ModuleDescriptor#isOpen open} module with a package in the

     * module. </p>

     *

     * <p> This method does not check if the given module reads this module. </p>

     *

     * @param  pn

     *         The package name

     *

     * @return {@code true} if this module has <em>opened</em> the package

     *         unconditionally

     *

     * @see ModuleDescriptor#opens()

     */

    public boolean isOpen(String pn) {

        Objects.requireNonNull(pn);

        return implIsExportedOrOpen(pn, EVERYONE_MODULE, /*open*/true);

    }

    /**

     * Returns {@code true} if this module exports or opens the given package

     * to the given module. If the other module is {@code EVERYONE_MODULE} then

     * this method tests if the package is exported or opened unconditionally.

     */

    private boolean implIsExportedOrOpen(String pn, Module other, boolean open) {

        // all packages in unnamed modules are open

        if (!isNamed())

            return true;

        // all packages are exported/open to self

        if (other == this && descriptor.packages().contains(pn))

            return true;

        // all packages in open and automatic modules are open

        if (descriptor.isOpen() || descriptor.isAutomatic())

            return descriptor.packages().contains(pn);

        // exported/opened via module declaration/descriptor

        if (isStaticallyExportedOrOpen(pn, other, open))

            return true;

        // exported via addExports/addOpens

        if (isReflectivelyExportedOrOpen(pn, other, open))

            return true;

        // not exported or open to other

        return false;

    }

    /**

     * Returns {@code true} if this module exports or opens a package to

     * the given module via its module declaration or CLI options.

     */

    private boolean isStaticallyExportedOrOpen(String pn, Module other, boolean open) {

        // test if package is open to everyone or <other>

        Map<String, Set<Module>> openPackages = this.openPackages;

        if (openPackages != null && allows(openPackages.get(pn), other)) {

            return true;

        }

        if (!open) {

            // test package is exported to everyone or <other>

            Map<String, Set<Module>> exportedPackages = this.exportedPackages;

            if (exportedPackages != null && allows(exportedPackages.get(pn), other)) {

                return true;

            }

        }

        return false;

    }

    /**

     * Returns {@code true} if targets is non-null and contains EVERYONE_MODULE

     * or the given module. Also returns true if the given module is an unnamed

     * module and targets contains ALL_UNNAMED_MODULE.

     */

    private boolean allows(Set<Module> targets, Module module) {

       if (targets != null) {

           if (targets.contains(EVERYONE_MODULE))

               return true;

           if (module != EVERYONE_MODULE) {

               if (targets.contains(module))

                   return true;

               if (!module.isNamed() && targets.contains(ALL_UNNAMED_MODULE))

                   return true;

           }

        }

        return false;

    }

    /**

     * Returns {@code true} if this module reflectively exports or opens the

     * given package to the given module.

     */

    private boolean isReflectivelyExportedOrOpen(String pn, Module other, boolean open) {

        // exported or open to all modules

        Map<String, Boolean> exports = ReflectionData.exports.get(this, EVERYONE_MODULE);

        if (exports != null) {

            Boolean b = exports.get(pn);

            if (b != null) {

                boolean isOpen = b.booleanValue();

                if (!open || isOpen) return true;

            }

        }

        if (other != EVERYONE_MODULE) {

            // exported or open to other

            exports = ReflectionData.exports.get(this, other);

            if (exports != null) {

                Boolean b = exports.get(pn);

                if (b != null) {

                    boolean isOpen = b.booleanValue();

                    if (!open || isOpen) return true;

                }

            }

            // other is an unnamed module && exported or open to all unnamed

            if (!other.isNamed()) {

                exports = ReflectionData.exports.get(this, ALL_UNNAMED_MODULE);

                if (exports != null) {

                    Boolean b = exports.get(pn);

                    if (b != null) {

                        boolean isOpen = b.booleanValue();

                        if (!open || isOpen) return true;

                    }

                }

            }

        }

        return false;

    }

    /**

     * Returns {@code true} if this module reflectively exports the

     * given package to the given module.

     */

    boolean isReflectivelyExported(String pn, Module other) {

        return isReflectivelyExportedOrOpen(pn, other, false);

    }

    /**

     * Returns {@code true} if this module reflectively opens the

     * given package to the given module.

     */

    boolean isReflectivelyOpened(String pn, Module other) {

        return isReflectivelyExportedOrOpen(pn, other, true);

    }

    /**

     * If the caller's module is this module then update this module to export

     * the given package to the given module.

     *

     * <p> This method has no effect if the package is already exported (or

     * <em>open</em>) to the given module. </p>

     *

     * @apiNote As specified in section 5.4.3 of the <cite>The Java&trade;

     * Virtual Machine Specification </cite>, if an attempt to resolve a

     * symbolic reference fails because of a linkage error, then subsequent

     * attempts to resolve the reference always fail with the same error that

     * was thrown as a result of the initial resolution attempt.

     *

     * @param  pn

     *         The package name

     * @param  other

     *         The module

     *

     * @return this module

     *

     * @throws IllegalArgumentException

     *         If {@code pn} is {@code null}, or this is a named module and the

     *         package {@code pn} is not a package in this module

     * @throws IllegalCallerException

     *         If this is a named module and the caller's module is not this

     *         module

     *

     * @jvms 5.4.3 Resolution

     * @see #isExported(String,Module)

     */

    @CallerSensitive

    public Module addExports(String pn, Module other) {

        if (pn == null)

            throw new IllegalArgumentException("package is null");

        Objects.requireNonNull(other);

        if (isNamed()) {

            Module caller = getCallerModule(Reflection.getCallerClass());

            if (caller != this) {

                throw new IllegalCallerException(caller + " != " + this);

            }

            implAddExportsOrOpens(pn, other, /*open*/false, /*syncVM*/true);

        }

        return this;

    }

    /**

     * If this module has <em>opened</em> a package to at least the caller

     * module then update this module to open the package to the given module.

     * Opening a package with this method allows all types in the package,

     * and all their members, not just public types and their public members,

     * to be reflected on by the given module when using APIs that support

     * private access or a way to bypass or suppress default Java language

     * access control checks.

     *

     * <p> This method has no effect if the package is already <em>open</em>

     * to the given module. </p>

     *

     * @apiNote This method can be used for cases where a <em>consumer

     * module</em> uses a qualified opens to open a package to an <em>API

     * module</em> but where the reflective access to the members of classes in

     * the consumer module is delegated to code in another module. Code in the

     * API module can use this method to open the package in the consumer module

     * to the other module.

     *

     * @param  pn

     *         The package name

     * @param  other

     *         The module

     *

     * @return this module

     *

     * @throws IllegalArgumentException

     *         If {@code pn} is {@code null}, or this is a named module and the

     *         package {@code pn} is not a package in this module

     * @throws IllegalCallerException

     *         If this is a named module and this module has not opened the

     *         package to at least the caller's module

     *

     * @see #isOpen(String,Module)

     * @see AccessibleObject#setAccessible(boolean)

     * @see java.lang.invoke.MethodHandles#privateLookupIn

     */

    @CallerSensitive

    public Module addOpens(String pn, Module other) {

        if (pn == null)

            throw new IllegalArgumentException("package is null");

        Objects.requireNonNull(other);

        if (isNamed()) {

            Module caller = getCallerModule(Reflection.getCallerClass());

            if (caller != this && (caller == null || !isOpen(pn, caller)))

                throw new IllegalCallerException(pn + " is not open to " + caller);

            implAddExportsOrOpens(pn, other, /*open*/true, /*syncVM*/true);

        }

        return this;

    }

    /**

     * Updates this module to export a package unconditionally.

     *

     * @apiNote This method is for JDK tests only.

     */

    void implAddExports(String pn) {

        implAddExportsOrOpens(pn, Module.EVERYONE_MODULE, false, true);

    }

    /**

     * Updates this module to export a package to another module.

     *

     * @apiNote Used by Instrumentation::redefineModule and --add-exports

     */

    void implAddExports(String pn, Module other) {

        implAddExportsOrOpens(pn, other, false, true);

    }

    /**

     * Updates this module to export a package to all unnamed modules.

     *

     * @apiNote Used by the --add-exports command line option.

     */

    void implAddExportsToAllUnnamed(String pn) {

        implAddExportsOrOpens(pn, Module.ALL_UNNAMED_MODULE, false, true);

    }

    /**

     * Updates this export to export a package unconditionally without

     * notifying the VM.

     *

     * @apiNote This method is for VM white-box testing.

     */

    void implAddExportsNoSync(String pn) {

        implAddExportsOrOpens(pn.replace('/', '.'), Module.EVERYONE_MODULE, false, false);

    }

    /**

     * Updates a module to export a package to another module without

     * notifying the VM.

     *

     * @apiNote This method is for VM white-box testing.

     */

    void implAddExportsNoSync(String pn, Module other) {

        implAddExportsOrOpens(pn.replace('/', '.'), other, false, false);

    }

    /**

     * Updates this module to open a package unconditionally.

     *

     * @apiNote This method is for JDK tests only.

     */

    void implAddOpens(String pn) {

        implAddExportsOrOpens(pn, Module.EVERYONE_MODULE, true, true);

    }

    /**

     * Updates this module to open a package to another module.

     *

     * @apiNote Used by Instrumentation::redefineModule and --add-opens

     */

    void implAddOpens(String pn, Module other) {

        implAddExportsOrOpens(pn, other, true, true);

    }

    /**

     * Updates this module to open a package to all unnamed modules.

     *

     * @apiNote Used by the --add-opens command line option.

     */

    void implAddOpensToAllUnnamed(String pn) {

        implAddExportsOrOpens(pn, Module.ALL_UNNAMED_MODULE, true, true);

    }

    /**

     * Updates a module to export or open a module to another module.

     *

     * If {@code syncVM} is {@code true} then the VM is notified.

     */

    private void implAddExportsOrOpens(String pn,

                                       Module other,

                                       boolean open,

                                       boolean syncVM) {

        Objects.requireNonNull(other);

        Objects.requireNonNull(pn);

        // all packages are open in unnamed, open, and automatic modules

        if (!isNamed() || descriptor.isOpen() || descriptor.isAutomatic())

            return;

        // check if the package is already exported/open to other

        if (implIsExportedOrOpen(pn, other, open)) {

            // if the package is exported/open for illegal access then we need

            // to record that it has also been exported/opened reflectively so

            // that the IllegalAccessLogger doesn't emit a warning.

            boolean needToAdd = false;

            if (!other.isNamed()) {

                IllegalAccessLogger l = IllegalAccessLogger.illegalAccessLogger();

                if (l != null) {

                    if (open) {

                        needToAdd = l.isOpenForIllegalAccess(this, pn);

                    } else {

                        needToAdd = l.isExportedForIllegalAccess(this, pn);

                    }

                }

            }

            if (!needToAdd) {

                // nothing to do

                return;

            }

        }

        // can only export a package in the module

        if (!descriptor.packages().contains(pn)) {

            throw new IllegalArgumentException("package " + pn

                                               + " not in contents");

        }

        // update VM first, just in case it fails

        if (syncVM) {

            if (other == EVERYONE_MODULE) {

                addExportsToAll0(this, pn);

            } else if (other == ALL_UNNAMED_MODULE) {

                addExportsToAllUnnamed0(this, pn);

            } else {

                addExports0(this, pn, other);

            }

        }

        // add package name to exports if absent

        Map<String, Boolean> map = ReflectionData.exports

            .computeIfAbsent(this, other,

                             (m1, m2) -> new ConcurrentHashMap<>());

        if (open) {

            map.put(pn, Boolean.TRUE);  // may need to promote from FALSE to TRUE

        } else {

            map.putIfAbsent(pn, Boolean.FALSE);

        }

    }

    /**

     * Updates a module to open all packages returned by the given iterator to

     * all unnamed modules.

     *

     * @apiNote Used during startup to open packages for illegal access.

     */

    void implAddOpensToAllUnnamed(Iterator<String> iterator) {

        if (jdk.internal.misc.VM.isModuleSystemInited()) {

            throw new IllegalStateException("Module system already initialized");

        }

        // replace this module's openPackages map with a new map that opens

        // the packages to all unnamed modules.

        Map<String, Set<Module>> openPackages = this.openPackages;

        if (openPackages == null) {

            openPackages = new HashMap<>();

        } else {

            openPackages = new HashMap<>(openPackages);

        }

        while (iterator.hasNext()) {

            String pn = iterator.next();

            Set<Module> prev = openPackages.putIfAbsent(pn, ALL_UNNAMED_MODULE_SET);

            if (prev != null) {

                prev.add(ALL_UNNAMED_MODULE);

            }

            // update VM to export the package

            addExportsToAllUnnamed0(this, pn);

        }

        this.openPackages = openPackages;

    }

    // -- services --

    /**

     * If the caller's module is this module then update this module to add a

     * service dependence on the given service type. This method is intended

     * for use by frameworks that invoke {@link java.util.ServiceLoader

     * ServiceLoader} on behalf of other modules or where the framework is

     * passed a reference to the service type by other code. This method is

     * a no-op when invoked on an unnamed module or an automatic module.

     *

     * <p> This method does not cause {@link Configuration#resolveAndBind

     * resolveAndBind} to be re-run. </p>

     *

     * @param  service

     *         The service type

     *

     * @return this module

     *

     * @throws IllegalCallerException

     *         If this is a named module and the caller's module is not this

     *         module

     *

     * @see #canUse(Class)

     * @see ModuleDescriptor#uses()

     */

    @CallerSensitive

    public Module addUses(Class<?> service) {

        Objects.requireNonNull(service);

        if (isNamed() && !descriptor.isAutomatic()) {

            Module caller = getCallerModule(Reflection.getCallerClass());

            if (caller != this) {

                throw new IllegalCallerException(caller + " != " + this);

            }

            implAddUses(service);

        }

        return this;

    }

    /**

     * Update this module to add a service dependence on the given service

     * type.

     */

    void implAddUses(Class<?> service) {

        if (!canUse(service)) {

            ReflectionData.uses.putIfAbsent(this, service, Boolean.TRUE);

        }

    }

    /**

     * Indicates if this module has a service dependence on the given service

     * type. This method always returns {@code true} when invoked on an unnamed

     * module or an automatic module.

     *

     * @param  service

     *         The service type

     *

     * @return {@code true} if this module uses service type {@code st}

     *

     * @see #addUses(Class)

     */

    public boolean canUse(Class<?> service) {

        Objects.requireNonNull(service);

        if (!isNamed())

            return true;

        if (descriptor.isAutomatic())

            return true;

        // uses was declared

        if (descriptor.uses().contains(service.getName()))

            return true;

        // uses added via addUses

        return ReflectionData.uses.containsKeyPair(this, service);

    }

    // -- packages --

    /**

     * Returns the set of package names for the packages in this module.

     *

     * <p> For named modules, the returned set contains an element for each

     * package in the module. </p>

     *

     * <p> For unnamed modules, this method is the equivalent to invoking the

     * {@link ClassLoader#getDefinedPackages() getDefinedPackages} method of

     * this module's class loader and returning the set of package names. </p>

     *

     * @return the set of the package names of the packages in this module

     */

    public Set<String> getPackages() {

        if (isNamed()) {

            return descriptor.packages();

        } else {

            // unnamed module

            Stream<Package> packages;

            if (loader == null) {

                packages = BootLoader.packages();

            } else {

                packages = loader.packages();

            }

            return packages.map(Package::getName).collect(Collectors.toSet());

        }

    }

    // -- creating Module objects --

    /**

     * Defines all module in a configuration to the runtime.

     *

     * @return a map of module name to runtime {@code Module}

     *

     * @throws IllegalArgumentException

     *         If defining any of the modules to the VM fails

     */

    static Map<String, Module> defineModules(Configuration cf,

                                             Function<String, ClassLoader> clf,

                                             ModuleLayer layer)

    {

        boolean isBootLayer = (ModuleLayer.boot() == null);

        int cap = (int)(cf.modules().size() / 0.75f + 1.0f);

        Map<String, Module> nameToModule = new HashMap<>(cap);

        Map<String, ClassLoader> nameToLoader = new HashMap<>(cap);

        Set<ClassLoader> loaders = new HashSet<>();

        boolean hasPlatformModules = false;

        // map each module to a class loader

        for (ResolvedModule resolvedModule : cf.modules()) {

            String name = resolvedModule.name();

            ClassLoader loader = clf.apply(name);

            nameToLoader.put(name, loader);

            if (loader == null || loader == ClassLoaders.platformClassLoader()) {

                if (!(clf instanceof ModuleLoaderMap.Mapper)) {

                    throw new IllegalArgumentException("loader can't be 'null'"

                            + " or the platform class loader");

                }

                hasPlatformModules = true;

            } else {

                loaders.add(loader);

            }

        }

        // define each module in the configuration to the VM

        for (ResolvedModule resolvedModule : cf.modules()) {

            ModuleReference mref = resolvedModule.reference();

            ModuleDescriptor descriptor = mref.descriptor();

            String name = descriptor.name();

            ClassLoader loader = nameToLoader.get(name);

            Module m;

            if (loader == null && name.equals("java.base")) {

                // java.base is already defined to the VM

                m = Object.class.getModule();

            } else {

                URI uri = mref.location().orElse(null);

                m = new Module(layer, loader, descriptor, uri);

            }

            nameToModule.put(name, m);

        }

        // setup readability and exports/opens

        for (ResolvedModule resolvedModule : cf.modules()) {

            ModuleReference mref = resolvedModule.reference();

            ModuleDescriptor descriptor = mref.descriptor();

            String mn = descriptor.name();

            Module m = nameToModule.get(mn);

            assert m != null;

            // reads

            Set<Module> reads = new HashSet<>();

            // name -> source Module when in parent layer

            Map<String, Module> nameToSource = Collections.emptyMap();

            for (ResolvedModule other : resolvedModule.reads()) {

                Module m2 = null;

                if (other.configuration() == cf) {

                    // this configuration

                    m2 = nameToModule.get(other.name());

                    assert m2 != null;

                } else {

                    // parent layer

                    for (ModuleLayer parent: layer.parents()) {

                        m2 = findModule(parent, other);

                        if (m2 != null)

                            break;

                    }

                    assert m2 != null;

                    if (nameToSource.isEmpty())

                        nameToSource = new HashMap<>();

                    nameToSource.put(other.name(), m2);

                }

                reads.add(m2);

                // update VM view

                addReads0(m, m2);

            }

            m.reads = reads;

            // automatic modules read all unnamed modules

            if (descriptor.isAutomatic()) {

                m.implAddReads(ALL_UNNAMED_MODULE, true);

            }

            // exports and opens, skipped for open and automatic

            if (!descriptor.isOpen() && !descriptor.isAutomatic()) {

                if (isBootLayer && descriptor.opens().isEmpty()) {

                    // no open packages, no qualified exports to modules in parent layers

                    initExports(m, nameToModule);

                } else {

                    initExportsAndOpens(m, nameToSource, nameToModule, layer.parents());

                }

            }

        }

        // if there are modules defined to the boot or platform class loaders

        // then register the modules in the class loader's services catalog

        if (hasPlatformModules) {

            ClassLoader pcl = ClassLoaders.platformClassLoader();

            ServicesCatalog bootCatalog = BootLoader.getServicesCatalog();

            ServicesCatalog pclCatalog = ServicesCatalog.getServicesCatalog(pcl);

            for (ResolvedModule resolvedModule : cf.modules()) {

                ModuleReference mref = resolvedModule.reference();

                ModuleDescriptor descriptor = mref.descriptor();

                if (!descriptor.provides().isEmpty()) {

                    String name = descriptor.name();

                    Module m = nameToModule.get(name);

                    ClassLoader loader = nameToLoader.get(name);

                    if (loader == null) {

                        bootCatalog.register(m);

                    } else if (loader == pcl) {

                        pclCatalog.register(m);

                    }

                }

            }

        }

        // record that there is a layer with modules defined to the class loader

        for (ClassLoader loader : loaders) {

            layer.bindToLoader(loader);

        }

        return nameToModule;

    }

    /**

     * Find the runtime Module corresponding to the given ResolvedModule

     * in the given parent layer (or its parents).

     */

    private static Module findModule(ModuleLayer parent,

                                     ResolvedModule resolvedModule) {

        Configuration cf = resolvedModule.configuration();

        String dn = resolvedModule.name();

        return parent.layers()

                .filter(l -> l.configuration() == cf)

                .findAny()

                .map(layer -> {

                    Optional<Module> om = layer.findModule(dn);

                    assert om.isPresent() : dn + " not found in layer";

                    Module m = om.get();

                    assert m.getLayer() == layer : m + " not in expected layer";

                    return m;

                })

                .orElse(null);

    }

    /**

     * Initialize/setup a module's exports.

     *

     * @param m the module

     * @param nameToModule map of module name to Module (for qualified exports)

     */

    private static void initExports(Module m, Map<String, Module> nameToModule) {

        Map<String, Set<Module>> exportedPackages = new HashMap<>();

        for (Exports exports : m.getDescriptor().exports()) {

            String source = exports.source();

            if (exports.isQualified()) {

                // qualified exports

                Set<Module> targets = new HashSet<>();

                for (String target : exports.targets()) {

                    Module m2 = nameToModule.get(target);

                    if (m2 != null) {

                        addExports0(m, source, m2);

                        targets.add(m2);

                    }

                }

                if (!targets.isEmpty()) {

                    exportedPackages.put(source, targets);

                }

            } else {

                // unqualified exports

                addExportsToAll0(m, source);

                exportedPackages.put(source, EVERYONE_SET);

            }

        }

        if (!exportedPackages.isEmpty())

            m.exportedPackages = exportedPackages;

    }

    /**

     * Initialize/setup a module's exports.

     *

     * @param m the module

     * @param nameToSource map of module name to Module for modules that m reads

     * @param nameToModule map of module name to Module for modules in the layer

     *                     under construction

     * @param parents the parent layers

     */

    private static void initExportsAndOpens(Module m,

                                            Map<String, Module> nameToSource,

                                            Map<String, Module> nameToModule,

                                            List<ModuleLayer> parents) {

        ModuleDescriptor descriptor = m.getDescriptor();

        Map<String, Set<Module>> openPackages = new HashMap<>();

        Map<String, Set<Module>> exportedPackages = new HashMap<>();