Operating system Dead lock
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This document discusses deadlock avoidance techniques. It explains the concepts of safe and unsafe states when allocating resources to processes. The resource allocation graph algorithm uses claim and assignment edges to model potential resource requests. Banker's algorithm requires processes to declare maximum resource needs upfront. It uses an allocation matrix and need matrix to determine if allocating resources to a process will result in an unsafe state. An example demonstrates tracking available resources and determining if processes can safely obtain requested resources without causing deadlock.
Operating system Dead lock
- 1. Karam Butt
- 2. DEADLOCK AVOIDANCE Contents Deadlock Avoidance Safe state Unsafe state Resource allocation graph algorithm Banker’s Algorithm
- 3. Deadlock Avoidance Deadlock avoidance is a technique used to avoid deadlock. It requires information about how different processes would request different resources. Safe state: if deadlock not occur then safe state. Unsafe state: if deadlock occur then unsafe state. The idea of avoiding a deadlock is simply not allow the system to enter an unsafe state the may cause a deadlock.
- 4. Resource Allocation Graph Algorithim Claim edge: used to indicate that process may request a resource in future.. It represented by dashed lined. Claim edge converts to Assignment edge when a process requests a resource. Assignment Edge is represented by solid line. When a resource is released by a process, assignment edge reconverts to a claim edge.
- 5. Example Resource-Allocation Graph For Deadlock Avoidance Safe state:
- 6. Example Resource-Allocation Graph For Deadlock Avoidance Unsafe
- 7. Banker’s Alghorithum Multiple instances. Each process must a priori claim maximum use. When a process requests a resource it may have to wait. When a process gets all its resources it must return them in a finite amount of time.
- 8. Example Banker’s Algorithm Example: If we Process A B C D P1 2 0 1 1 P2 0 1 0 0 P3 1 0 1 1 P4 1 1 0 1 Allocation Matrix Available resource(5,2,4,3) Allocation resources (4,2,2,3)
- 9. Need matrix Process A B C D P1 1 1 0 0 P2 0 1 1 2 P3 3 1 0 0 P4 0 0 1 0
- 10. Solve the Example Available free resources=Available resource –Allocated resources Available free resources=(5,2,4,3)-(4,2,2,3) Available free resources=(1,0,2,0) Working of Banker’s Algorithm: Need Resources <=Available free Resources(when the condition is satisfied then processes in safe state otherwise not.) For p1: (1,1,0,0)<=(1,0,2,0) Unsafe state (not Available)
- 11. Continue……… For p2: (0,1,1,2)<=(1,0,2,0) Unsafe(Not Available) For p3: (3,,1,0,0)<=(1,0,2,0) Unsafe(Not Available) For p4: (0,,0,1,0)<=(1,0,2,0) (Available) Safe Now the process p4 complete, it will turn over currently allocated resources ,incrementing the available free resources..
- 12. Updated value of Available Resource=Current value of available Resources + Allocated resources of Allocated matrix Need process(p1)=(1,1,0,0)<=(2,1,2,1) Available Now p1 is complete, it will turn over currently allocated resources ,incrementing the available free resources.. (1.1,0,1) Allocation of process(p4) (2,1,2,1) updated value of Available
- 13. (2,1,2,1) Current value of Available (2,0,1,1) Allocation process (P1) (4,1,3,2) Updated value of Available