Advanced alloys usually contain a high density of interfaces. When they are subjected to a high strain-rate deformation, the interaction between the dislocation-mediated plastic flow and those interfaces dictate their overall performances. During a dislocation-interface reaction, a pile up may form and introduce a complex local stress. Such a process is multiscale in nature because the atomic-level structure change and the long-range stress accumulation simultaneously occur. Here we present a concurrent atomistic-continuum (CAC) method for (i) characterizing the instantaneous stress field during the formation of a micrometer-level dislocation pileup; and (ii) determining its role in the subsequent structure change. Taking the amorphous/crystalline (A/C) and crystalline/crystalline (C/C) metallic composites as model materials, with a fully atomistic resolution at the interface and coarse-grained atomistic resolution in the regions away from interfaces, CAC models require significantly less computational cost than that by fully atomistic models. Most importantly, the atomistic natures (core reconstruction and phonon emission) of fast moving dislocations are preserved in the coarse region. By this way, CAC simulations enable a direct quantification of the long-range stress state that controls the atomic-level structure change. The full suite of mechanisms responsible for a dislocation-interface reaction will be revealed. In CuZr/Cu, with the dislocations hitting the A/C interfaces, strong local stress concentrations near the interface lead to instability of amorphous phases. In contrast, in C/C nanolaminates, dislocation pile-ups at the interface is found to activate a phase transformation. Our results elucidate the discrepancies between atomistic simulations and experimental observations, and highlight the importance of modeling dislocation-interfaces reactions using a concurrent multiscale method.