Background on concurrent processing
Conceptually, it can help to think of concurrent processing by imagining a group of people who can't see each other and are trying to collaborate on a task. Perhaps their vision is impaired or blocked by screens, or their workspace has awkward doorways they can't quite see through. These people can, however, pass tokens, notes, and work-in-process to each other.
Imagine a small delicatessen in an old seaside resort city (on the Atlantic coast of the US) with an awkward countertop layout. The two sandwich chefs can't see or hear each other. While the owner can afford to pay two fine chefs, the owner can't afford more than one serving tray. Due to the awkward complications of the ancient building, the chefs can't really see the tray, either. They're forced to reach down below their counter to be sure the serving tray is in place. Then, assured the tray is there, they carefully place their work of art – complete...