Banker's Algorithm Calculator (Safe Sequence & Deadlock Detection)

The Banker's algorithm decides whether a system with several resource types is in a safe state — whether there is an order in which every process can obtain what it may still need and finish — and whether a new request can be granted without losing that safety. This calculator builds the Need matrix, runs the safety algorithm step by step with the Work vector, checks a resource request, and also runs the related deadlock-detection algorithm on a Request matrix.

How to use this tool

1. Enter the Allocation matrix, one process per line (P0: 0 1 0).
2. Enter the Max matrix (or the Request matrix for deadlock detection) in the same order.
3. Enter the Available vector, or the total instances of each resource.
4. Optionally enter a request such as P1 1 0 2 and read whether it is granted.

Formula

Need = Max − Allocation · Work = Available; repeat: find Pᵢ with Need ≤ Work, then Work = Work + Allocationᵢ · safe if every process finishes

A request from Pᵢ is an error if it exceeds Need, must wait if it exceeds Available, and otherwise is granted only if the state after pretending to allocate it is still safe. Deadlock detection uses the current Request instead of Need and marks processes that hold nothing as finished from the start; those that never finish are deadlocked. Several safe sequences may exist — the search order option reproduces the two common ways of tracing it.

Example

The sample is the textbook example of Silberschatz's Operating System Concepts: 5 processes, resources A, B, C, Available (3, 3, 2). Need is P0 (7,4,3), P1 (1,2,2), P2 (6,0,0), P3 (0,1,1), P4 (4,3,1). P1 can finish first (Work becomes 5 3 2), then P3 (7 4 3), P4 (7 4 5), P0 (7 5 5) and P2 (10 5 7), so the state is safe with the sequence <P1, P3, P4, P0, P2>. The request (1, 0, 2) by P1 is granted.