Banker’s algorithm in operating system (OS) -Advantages – Disadvantages

By: Prof. Fazal Rehman Shamil
Last modified on August 27th, 2020

What is Banker’s algorithm

Banker’s algorithm is an algorithm to avoid deadlock and to allocate resources to the processes safely. Banker’s algorithm helps the operating system to successfully share the resources among all the processes. 

Let’s discuss with an example;

Examples of bankers algorithm

Example 1

bankers algorithm Operating systems Step by step
Figure: bankers algorithm Operating systems –  Step by step

Example 2

Process Total instances of Resource A Total instances of Resource B Total instances of Resource C
P0 0 1 0
P1 2 0 0
P2 3 0 2
P3 2 1 1
P4 0 0 2

Table: Showing resources already processes occupies

Note: PCB manage the memory by keeping a record of the allocated resources and free resources.

Explanation of the table

Process P0 already has 0 resource instances of A, 1 resource instance of B, and similarly 0 resource instance of C.

Process P1 already has 2 resource instances of A, 0 resource instance of B, and similarly 0 resource instance of C.

Process P2 already have 3 resource instances of A, 0 resource instance of B, and similarly 2 resource instance of C.

Process P3 already has 2 resource instances of A, 1 resource instance of B, and similarly 1 resource instance of C.

Process P4 already have 0 resource instances of A, 0 resource instance of B, and similarly 2 resource instance of C.

Process Total instances of Resource A Total instances of Resource B Total instances of Resource C
P0 7 5 3
P1 3 2 2
P2 9 0 2
P3 2 2 2
P4 4 3 3

Table: Showing maximum resources required for complete execution.

Explanation of the table

Process P0 requires a maximum of 7 resource instances of A, 51 resource instances of B, and similarly 3 resource instances of C for the successful execution.
Process P1 requires a maximum of 3 resource instances of A, 2 resource instance of B, and similarly 2 resource instances of C for the successful execution.
Process P2 requires a maximum of 9 resource instances of A, 0 resource instance of B, and similarly 2 resource instances of C for the successful execution.
Process P3 requires a maximum of 2 resource instances of A, 2 resource instance of B, and similarly 2 resource instances of C for the successful execution.
Process P4 requires a maximum of 4 resource instances of A, 3 resource instance of B, and similarly 3 resource instances of C for the successful execution.

Process Total instances of Resource A Total instances of Resource B Total instances of Resource C
P0 7 4 3
P1 1 2 2
P2 6 0 0
P3 0 1 1
P4 4 3 1

Table: Showing needed resources to each process for execution.

We can get the needed resources with the help of the following formula;

Needed resources = maximum resources – allocated resources

 Process Total instances of Resource A Total instances of Resource B Total instances of Resource C
P0 3 3 2
P1 5 3 2
P2 5 3 2
P3 7 4 3
P4 7 4 5
P0 7 5 5
P2 10 5 7

Table: Showing available free resources for each process.

Now compare available free resources of each process with its needed resources. The needed matrix should less than/equal as compared to the available matrix for process execution.

First iteration:

P0=finish[p0]=False              can’t execute because if we assign free resources 

to P0, and we add the free resources of P0 with

needed resources of P0, it still does not fulfill the

the requirement of maximum resources needed to P0 for

it’s execution.

P1=FINISH[P1]=TRUE         can execute

P2=FINISH[P2]=False          can’t execute

P3=FINSH[P3]=TRUE          can execute

P4=FINISH[P4]=TRUE         can execute

2nd iteration:

P0=FINISH[P0]=TRUE          can execute

P2=FINISH[P2]=TRUE         can execute

 

Example 3

Allocated Resources

A B C
P1 2 0 1
P2 5 2 6
P3 3 1 5
P4 4 0 9

 Maximum Resources

A B C
P1 3 5 4
P2 9 2 8
P3 5 7 5
P4 8 6 10

Needed Resources

A B C
P1 1 5 3
P2 4 0 2
P3 2 6 0
P4 4 6 1

Free Resources

A B C
3 7 2

P1= fails ( as the number of needed resources are greater than the free resources)

P2=fails ( as the number of needed resources are greater than the free resources)

P3= works and executes

After the execution of P3, it releases its allocated resources as well so that the number of free resources increased.

  Free Resources

A B C
6 8 7

P4= works and executes

After the execution of P4, it releases its allocated resources to increased the number of free resources.

Free ResourceP1

A B C
10 8 16

P1= works and executes

After the execution of P1, it releases its allocated resources to increased the number of free resources.

Free Resources

A B C
12 8 17

P2= works and executes

After the execution of P2, it releases its allocated resources to increased the number of free resources.

Free Resources

A B C
15 10 23

These are the free resources when all the processes execute successfully.

Click Below to Download Implementation file

Bankers algorithm implementation Operating Systems (OS)

Advantages of Banker’s algorithm

Banker’s algorithm Avoids deadlock and it is less restrictive than deadlock prevention.

Disadvantages of Banker’s algorithm

It only works with a fixed number of resources and processes.

Banker Algorithm code in C

Here, i am sharing with you the banker algorithm code in C.

Output

banker algorithm code in c

Frequently Asked Questions (FAQ)

Who developed the banker’s algorithm?
Edsger Dijkstra developed the banker’s algorithm.

Excercise

Answer the following questions using the bankers algorithm.

  • System is in safe state or not?
  • How you will apply bankers algorithm on the given data.
Allocation Max Available
A B C D A B C D A B C D
P1 4111 4414 7741
P1 7141 5454
P4 4117 4716
P7 1714 1444
P4 1474 7665
Prof. Fazal Rehman Shamil
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