Using particle-based simulation of a soft, coarse-grained model and self-consistent field theory (SCFT), we investigate the properties of dense living polymer systems with ring formation both in the bulk and in thin films. In the bulk, our results confirm that the molecular weight distribution of ring polymers exhibits a combination of an exponential decay and a power law. The exponential molecular weight distribution of linear chains is hardly affected by ring formation, only the corresponding mean molecular weight is slightly reduced. At lower segment density, the fraction of monomers of ring polymers is increased. In thin films, ring formation does not influence the width of the narrow interface, where the segment density rises to the bulk value. Since the molecular extension of ring polymers is smaller than that of linear chains, the spatial extent of the wide interphase is, however, reduced. In the narrow interface, we find that the local ring formation is affected by five aspects: (1) the mirroring of chain conformations and back-folding by the solid substrate (Silberberg argument) and other four aspects at the solid substrate, i.e., (2) the reduced segment density, (3) the enrichment of chain ends, (4) the pronounced segregation of nonbonded monomers, and (5) the reduced dimensionality of ring polymers. In the wide interphase, the local ring formation is enhanced mainly by the first aspect. By comparing the results from the particle-based simulation and SCFT, we observe good agreement in the wide interphase, but the difference in the local structure leads to differences in the narrow interface. Additionally, the SCFT results show that a decrease of the film thickness increases the global ring formation within the thin film.