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);

                Model model = findRawModel(from, gId, aId);
                if (model != null) {
                    context.modelByGA.put(new GAKey(gId, aId), new Holder(model));
                    context.modelByPath.put(model.getPomFile(), new Holder(model));
                }
                return model;
            }

            @Override
            public Model getRawModel(Path from, Path path) {

         * processes one artifact at a time and hence cannot associate the artifacts from the same project to use the
         * same version index. Allowing the caller to pass in metadata from a previous deployment allows to re-establish
         * the association between the artifacts of the same project.
         */

                    MojoNotFoundException, InvalidPluginDescriptorException {
        /*
         * Initialize mapping from lifecycle phase to bound mojos. The key set of this map denotes the phases the caller
         * is interested in, i.e. all phases up to and including the specified phase.
         */

        Map<String, Map<Integer, List<MojoExecution>>> mappings = new LinkedHashMap<>();

         * processes one artifact at a time and hence cannot associate the artifacts from the same project to use the
         * same timestamp+buildno for the snapshot versions. Allowing the caller to pass in metadata from a previous
         * deployment allows to re-establish the association between the artifacts of the same project.
         */
        for (Metadata metadata : request.getMetadata()) {

     */
    @Nullable
    Path getPath();

    /**
     * Creates a new byte stream to the source contents.
     * Closing the returned stream is the responsibility of the caller.
     *
     * @return a byte stream to the source contents, never {@code null}
     * @throws IOException in case of IO issue
     */
    @Nonnull
    InputStream openStream() throws IOException;

    /**

    }

    protected DefaultModelRepositoryHolder(DefaultModelRepositoryHolder holder) {
        this.session = holder.session;
        this.repositoryMerging = holder.repositoryMerging;
        this.pomRepositories = List.copyOf(holder.pomRepositories);
        this.externalRepositories = List.copyOf(holder.externalRepositories);
        this.repositories = List.copyOf(holder.repositories);
    }

    @Override

     *
     * @param session The session to use to resolve the model, must not be {@code null}.
     * @param parent The parent coordinates to resolve, must not be {@code null}.
     * @param modified a holder for the updated parent, must not be {@code null}.
     * @return The source of the requested POM, never {@code null}.
     * @throws ModelResolverException If the POM could not be resolved from any configured repository.
     */

 *
 * @since 4.0.0
 */
@Experimental
public interface PathType {
    /**
     * The type for all paths that could not be placed in any of the types requested by a caller.
     * This type can appear in the return value of a call to
     * {@link Session#resolveDependencies resolveDependencies(...)} when at least one dependency

public interface RepositorySystemSessionFactory {
    /**
     * Creates "ready to use" session builder instance. The factory does not set up one thing: the
     * {@link org.eclipse.aether.repository.WorkspaceReader}s, that is caller duty to figure out. Workspace readers
     * should be set up as very last thing before using resolver session, that is built by invoking
     * {@link SessionBuilder#build()} method.
     *