Deadlock Analysis

Deadlock Detection

Graph cycle analysis identifying deadlocks in concurrent wait systems.

What is Deadlock Detection?

Deadlock Detection processes locate deadlocks in system resource allocations. A Wait-For Graph (WFG) is constructed where processes are vertices, and edges represent dependencies. A cycle in this graph indicates the presence of a deadlock. Cycles are identified using Depth-First Search (DFS) back-edge detection.

Key Characteristics:

  • Constructs processes dependency models dynamically.
  • Detects cycle loops using graph DFS traversals.
  • Determines deadlock recovery triggers.
  • Indicates safe vs blocked task components.

Complexity Analysis

Avg Time Complexity: O(V + E) where V is vertices (processes) and E is dependency edges
Space Complexity: O(V + E) storage maps
Best Case: O(1) (graph is empty/has no edges)
Worst Case: O(V + E) (visiting all elements recursively)

How it Works Step-by-Step

  1. Build Dependency Graph: Map processes waiting on resources to processes currently holding them.
  2. Initialize Status Maps: Maintain node statuses: 0=unvisited, 1=visiting, 2=visited.
  3. DFS Cycle Search: For each unvisited node, run DFS traversal.
  4. Back-edge Detection: During DFS, mark current node as 1. If a neighbor is marked 1, a cycle is detected.
  5. Complete: Mark node as 2 when its DFS finishes. If any cycle is found, deadlock is declared.

Code Implementation

Worked Trace Example

Process loops: P1 waiting on P2, P2 waiting on P3, P3 waiting on P1:
1. DFS from P1: visit P1 (1), go to P2.
2. DFS from P2: visit P2 (1), go to P3.
3. DFS from P3: visit P3 (1), go to P1.
4. Neighbor P1 has status (1) -> cycle detected!
Result: Deadlock detected between P1, P2, and P3.

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