"Message passing" might be considered a component of a "shared nothing" system. If so, a thread-based message passing implementation might still use shared proc

"Message passing" might be considered a component of a "shared nothing" system. If so, a thread-based message passing implementation might still use shared process memory behind the scenes to efficiently pass messages between local threads. Worker threads might be written so that the responsibility for managing a resource external to the process is assigned to max 1 thread simultaneously, even if the message passing abstraction uses a bit of shared process memory behind the scenes.