Courses/Distributed Systems

Distributed Systems

CS3.401

Prof. Kishore Kothapalli•Monsoon 2025-26•4 credits

Revision Notes/Unit 6 — Distributed Deadlock Detection

Unit 6 — Distributed Deadlock Detection

Resource request models (Single, AND, OR, AND-OR, P-out-of-Q). Wait-for graphs and the cycle-vs-knot distinction. Three handling strategies (prevention, avoidance, detection) and why detection dominates in DS. Detection algorithms: Ho-Ramamoorthy (centralised, 1-phase / 2-phase), Chandy-Misra-Haas probe (AND), Mitchell-Merritt label-passing (single-resource), Chandy diffusion (OR).

Resource Models, WFG, CMH Probe, Mitchell-Merritt, Chandy Diffusion

14 min

A deadlock in a distributed system is the same idea as in an OS — a cycle of processes each waiting for a resource held by another. But the DETECTION criterion depends on the resource model: in Single-resource and AND models a cycle in the wait-for graph suffices; in OR (a process needs any one of many resources) you need a stronger structure called a **knot** (an SCC with no outgoing edges). Three classical algorithms — Chandy-Misra-Haas probe, Mitchell-Merritt label-passing, Chandy diffusion — implement detection for different models.