// phase 1
        DefaultModelBuilderResult result = new DefaultModelBuilderResult();

        DefaultModelProblemCollector problems = new DefaultModelProblemCollector(result);

        // read and validate raw model
        Model fileModel = readFileModel(request, problems);
        result.setFileModel(fileModel);

        Model activatedFileModel = activateFileModel(fileModel, request, result, problems);

            attachedArtifacts.set(index, artifact);
        } else {
            attachedArtifacts.add(artifact);
        }
    }

    /**
     * Returns a read-only list of the attached artifacts to this project.
     *
     * @return the attached artifacts of this project
     */
    public List<Artifact> getAttachedArtifacts() {
        if (attachedArtifacts == null) {

            //
            // We need an executor that will not block.
            // We can't use work stealing, as we are building a graph
            // and this could lead to cycles where a thread waits for
            // a task to finish, then execute another one which waits
            // for the initial task...
            // In order to work around that problem, we override the