maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultTransformerContext.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.model.building;

import java.io.File;
import java.nio.file.Path;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Supplier;

import org.apache.maven.model.Model;
import org.apache.maven.model.locator.ModelLocator;

/**
 *
 * @since 4.0.0
 */
class DefaultTransformerContext implements TransformerContext {
    final ModelLocator modelLocator;

    final Map<String, String> userProperties = new ConcurrentHashMap<>();

    final Map<Path, Holder> modelByPath = new ConcurrentHashMap<>();

    final Map<GAKey, Holder> modelByGA = new ConcurrentHashMap<>();

    public static class Holder {
        private volatile boolean set;
        private volatile Model model;

        Holder() {}

        Holder(Model model) {
            this.model = Objects.requireNonNull(model);
            this.set = true;
        }

        public static Model deref(Holder holder) {
            return holder != null ? holder.get() : null;
        }

        public Model get() {
            if (!set) {
                synchronized (this) {
                    if (!set) {
                        try {
                            this.wait();
                        } catch (InterruptedException e) {
                            // Ignore
                        }
                    }
                }
            }
            return model;
        }

        public Model computeIfAbsent(Supplier<Model> supplier) {
            if (!set) {
                synchronized (this) {
                    if (!set) {
                        this.set = true;
                        this.model = supplier.get();
                        this.notifyAll();
                    }
                }
            }
            return model;
        }
    }

    DefaultTransformerContext(ModelLocator modelLocator) {
        this.modelLocator = modelLocator;
    }

    @Override
    public String getUserProperty(String key) {
        return userProperties.get(key);
    }

    @Override
    public Model getRawModel(Path from, Path p) {
        return Holder.deref(modelByPath.get(p));
    }

    @Override
    public Model getRawModel(Path from, String groupId, String artifactId) {
        return Holder.deref(modelByGA.get(new GAKey(groupId, artifactId)));
    }

    @Override
    public Path locate(Path path) {
        File file = modelLocator.locateExistingPom(path.toFile());
        return file != null ? file.toPath() : null;
    }

    static class GAKey {
        private final String groupId;
        private final String artifactId;
        private final int hashCode;

        GAKey(String groupId, String artifactId) {
            this.groupId = groupId;
            this.artifactId = artifactId;
            this.hashCode = Objects.hash(groupId, artifactId);
        }

        @Override
        public int hashCode() {
            return hashCode;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
            if (!(obj instanceof GAKey)) {
                return false;
            }

            GAKey other = (GAKey) obj;
            return Objects.equals(artifactId, other.artifactId) && Objects.equals(groupId, other.groupId);
        }
    }
}