Process Progress Diagram

operating-systems concurrency

Definition

Process Progress Diagram

A process progress diagram is a geometric tool used to visualise the execution paths of two or more processes competing for shared resources. It maps the progress of each process along perpendicular axes to identify unsafe regions where a deadlock becomes unavoidable.

Mechanism

• Axes: The horizontal axis represents the progress of Process $P_1$, and the vertical axis represents Process $P_2$.
• Resource Regions: Rectangular areas represent states where a resource is required by both processes. Because of mutual exclusion, the joint execution path cannot enter these areas.
• Unsafe Region: A region of the diagram from which every possible path (moving only right and up) must eventually lead into a “dead end” where both processes are blocked.

Significance

The diagram demonstrates that a system can be in a state that is not yet deadlocked, but from which a deadlock is inevitable regardless of future scheduling decisions. Deadlock avoidance strategies, such as the Banker’s algorithm, aim to ensure that the execution path never enters such an unsafe region.