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 * 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,

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 *

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package jdk.internal.module;

import java.lang.module.ModuleDescriptor;

import java.lang.module.ModuleDescriptor.Provides;

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.concurrent.ConcurrentHashMap;

import java.util.concurrent.CopyOnWriteArrayList;

import jdk.internal.loader.ClassLoaderValue;

/**

 * A <em>services catalog</em>. Each {@code ClassLoader} and {@code Layer} has

 * an optional {@code ServicesCatalog} for modules that provide services.

 *

 * @apiNote This class will be replaced once the ServiceLoader is further

 *          specified

 */

public final class ServicesCatalog {

    /**

     * Represents a service provider in the services catalog.

     */

    public final class ServiceProvider {

        private final Module module;

        private final String providerName;

        public ServiceProvider(Module module, String providerName) {

            this.module = module;

            this.providerName = providerName;

        }

        public Module module() {

            return module;

        }

        public String providerName() {

            return providerName;

        }

        @Override

        public int hashCode() {

            return Objects.hash(module, providerName);

        }

        @Override

        public boolean equals(Object ob) {

            if (!(ob instanceof ServiceProvider))

                return false;

            ServiceProvider that = (ServiceProvider)ob;

            return Objects.equals(this.module, that.module)

                    && Objects.equals(this.providerName, that.providerName);

        }

    }

    // service name -> list of providers

    private final Map<String, List<ServiceProvider>> map = new ConcurrentHashMap<>();

    private ServicesCatalog() { }

    /**

     * and lookup

     */

    public static ServicesCatalog create() {

        return new ServicesCatalog();

    }

    /**

     * Returns the list of service provides for the given service type

     * name, creating it if needed.

     */

    private List<ServiceProvider> providers(String service) {

        // avoid computeIfAbsent here

        List<ServiceProvider> list = map.get(service);

        if (list == null) {

            list = new CopyOnWriteArrayList<>();

            List<ServiceProvider> prev = map.putIfAbsent(service, list);

            if (prev != null)

                list = prev;  // someone else got there

        }

        return list;

    }

    /**

     * Registers the providers in the given module in this services catalog.

     */

    public void register(Module module) {

        ModuleDescriptor descriptor = module.getDescriptor();

        for (Provides provides : descriptor.provides()) {

            String service = provides.service();

            List<String> providerNames = provides.providers();

            int count = providerNames.size();

            if (count == 1) {

                String pn = providerNames.get(0);

                providers(service).add(new ServiceProvider(module, pn));

            } else {

                List<ServiceProvider> list = new ArrayList<>(count);

                for (String pn : providerNames) {

                    list.add(new ServiceProvider(module, pn));

                }

                providers(service).addAll(list);

            }

        }

    }

    /**

     * Add a provider in the given module to this services catalog

     *

     * @apiNote This method is for use by java.lang.instrument

     */

    public void addProvider(Module module, Class<?> service, Class<?> impl) {

        List<ServiceProvider> list = providers(service.getName());

        list.add(new ServiceProvider(module, impl.getName()));

    }

    /**

     * Returns the (possibly empty) list of service providers that implement

     * the given service type.

     */

    public List<ServiceProvider> findServices(String service) {

        return map.getOrDefault(service, List.of());

    }

    /**

     * Returns the ServicesCatalog for the given class loader or {@code null}

     * if there is none.

     */

    public static ServicesCatalog getServicesCatalogOrNull(ClassLoader loader) {

        return CLV.get(loader);

    }

    /**

     * Returns the ServicesCatalog for the given class loader, creating it if

     * needed.

     */

    public static ServicesCatalog getServicesCatalog(ClassLoader loader) {

        // CLV.computeIfAbsent(loader, (cl, clv) -> create());

        ServicesCatalog catalog = CLV.get(loader);

        if (catalog == null) {

            catalog = create();

            ServicesCatalog previous = CLV.putIfAbsent(loader, catalog);

            if (previous != null) catalog = previous;

        }

        return catalog;

    }

    // the ServicesCatalog registered to a class loader

    private static final ClassLoaderValue<ServicesCatalog> CLV = new ClassLoaderValue<>();

}