If a system does not employ either a deadlock prevention or deadlock avoidance algorithm then a deadlock situation may occur. In this case-
- Apply an algorithm to examine state of system to determine whether deadlock has has occurred or not.
- Apply an algorithm to recover from the deadlock. For more refer- Deadlock Recovery
Deadlock Detection Algorithm:
The algorithm employs several time varying data structures:
- Available- A vector of length m indicates the number of available resources of each type.
- Allocation- An n*m matrix defines the number of resources of each type currently allocated to a process. Column represents resource and resource represent process.
- Request- An n*m matrix indicates the current request of each process. If request[i][j] equals k then process Pi is requesting k more instances of resource type Rj.
We treat rows in the matrices Allocation and Request as vectors, we refer them as Allocationi and Requesti.
Steps of Algorithm:
- Let Work and Finish be vectors of length m and n respectively. Initialize Work= Available. For i=0, 1, …., n-1, if Allocationi = 0, then Finish[i] = true; otherwise, Finish[i]= false.
- Find an index i such that both
a) Finish[i] == false
b) Requesti <= Work
If no such i exists go to step 4.
- Work= Work+ Allocationi
Go to Step 2.
- If Finish[i]== false for some i, 0<=i<n, then the system is in a deadlocked state. Moreover, if Finish[i]==false the process Pi is deadlocked.
In this, Work = [0, 0, 0] &
Finish = [false, false, false, false, false]
- i=0 is selected as both Finish = false and [0, 0, 0]<=[0, 0, 0].
- Work =[0, 0, 0]+[0, 1, 0] =>[0, 1, 0] &
Finish = [true, false, false, false, false].
- i=2 is selected as both Finish = false and [0, 0, 0]<=[0, 1, 0].
- Work =[0, 1, 0]+[3, 0, 3] =>[3, 1, 3] &
Finish = [true, false, true, false, false].
- i=1 is selected as both Finish = false and [2, 0, 2]<=[3, 1, 3].
- Work =[3, 1, 3]+[2, 0, 0] =>[5, 1, 3] &
Finish = [true, true, true, false, false].
- i=3 is selected as both Finish = false and [1, 0, 0]<=[5, 1, 3].
- Work =[5, 1, 3]+[2, 1, 1] =>[7, 2, 4] &
Finish = [true, true, true, true, false].
- i=4 is selected as both Finish = false and [0, 0, 2]<=[7, 2, 4].
- Work =[7, 2, 4]+[0, 0, 2] =>[7, 2, 6] &
Finish = [true, true, true, true, true].
- Since Finish is a vector of all true it means there is no deadlock in this example.
- Operating System | Deadlock detection in Distributed systems
- Program for Deadlock free condition in Operating System
- Operating System | Process Management | Deadlock Introduction
- Deadlock Detection And Recovery
- Techniques used in centralized approach of deadlock detection in distributed systems
- Operating System | Banker's Algorithm
- Operating System | Bakery Algorithm
- Operating System | Dekker's algorithm
- Operating System | Program for Next Fit algorithm in Memory Management
- Operating System | Peterson's Algorithm (Using processes and shared memory)
- Operating System | Banker's Algorithm : Print all the safe state (or safe sequences)
- Operating System | Starvation and Aging in Operating Systems
- Operating System | Buddy System - Memory allocation technique
- Operating System | Semaphores in operating system
- Operating System | Introduction of Operating System - Set 1
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.
Improved By : EduardoNodarse