| Process |
R1 |
R2 |
R3 |
R4 |
| P1 |
1 |
2 |
3 |
1 |
| P2 |
2 |
1 |
0 |
2 |
| P3 |
2 |
0 |
1 |
0 |
So, currently, there are 2 of R1, 1 of R2, 1 of R3, and 1 of R4 free.
5. How many more resources does each process need?
To find how many more resources each process needs:
Resources Needed = Maximum Resources - Allocated Resources
| Process |
R1 |
R2 |
R3 |
R4 |
| P1 |
2 |
0 |
0 |
1 |
| P2 |
0 |
2 |
1 |
2 |
| P3 |
1 |
1 |
4 |
0 |
Steps to Allocate Resources Safely
Step 1: Process P1 can use the available resources <2,1,1,1> to complete its work. After finishing, it releases all its allocated and used resources. Total released = <3,3,4,2>
Step 2: Now the available resources are <3,3,4,2>. Both P2 and P3 can get their needed resources. If P2 runs next, after finishing, the available resources become <5,4,4,4>
Step 3: Finally, P3 uses <1,1,4,0> resources, finishes execution, and releases resources back to the system. Now all resources are restored to <7,4,5,4>
The execution order could be <P1, P2, P3> or <P1, P3, P2> depending on which process gets resources first. Both sequences are safe because the system never enters a deadlock.
Banker’s Algorithm for Deadlock Avoidance in OS
One of the most widely used approaches to resource safety management is the Banker’s algorithm in OS. It assists the operating system in making decisions on whether to permit or postpone a resource request of a process.
The objective of this algorithm is to maintain a safe state of the system and prevent deadlocks. The name comes from the way a banker grants loans, by ensuring safety before lending. A banker never lends the money unless they are sure that they will get the loan back safely. Similarly, the OS will allocate resources to processes only when it can guarantee that no process will get stuck.
Let’s explore the steps involved in the banker’s algorithm in detail.
Step 1: Initialize the System
The OS initially gathers all the information, such as the total amount of resources, the available resources, and the amount that each process can require. Such an arrangement can also assist the system in monitoring the free and used resources.
Step 2: Define a Request
A request is sent whenever a process requires additional resources. The system then checks whether the process is asking for more resources than its declared maximum and rejects the request if it does.
Step 3: Grant Request if Safe
The process is given the requested resources temporarily by the OS. After that, it examines whether the system will leave in a safe condition upon their granting. In case yes, the request is granted. Otherwise, the process takes time to wait until the resources are available.
Step 4: Verify Safe State
After giving out resources, the OS checks whether every process can still finish successfully. If all the processes can complete in the same order, the system is in a safe state. Otherwise, it cancels the resource request and keeps the system stable.
Step 5: Release Resources
Once a process completes its work, it gives back all the resources it used. The OS then updates the available resources so they can be given to other processes.
Resource Allocation Graph (RAG)
Resource Allocation Graph features a process vertex in the form of a circle and a resource vertex in the form of a box. The example of the resources is depicted by a dot within the box. Each resource can have a single or multiple instances. An example of a Resource Allocation Graph(RAG) is as below.
Difference Between Deadlock Prevention and Deadlock Avoidance
Both deadlock prevention and deadlock avoidance in OS are methods that are used to stop the deadlock, but they work in different ways
| Feature | Deadlock Prevention | Deadlock Avoidance | | Meaning | Deadlock prevention is the way of stopping deadlocks by removing the conditions that cause them. | Deadlock avoidance means allowing resource requests only when the system will still stay in a safe state. |
| Approach | It is a static method. The system follows fixed rules to avoid deadlocks. | It is a dynamic method. The system checks each request before granting it. |
| Flexibility | Less flexible because it restricts how processes can request resources. | More flexible because it allows requests if the system remains safe. |
| Resource Use | Sometimes resources stay unused because of strict rules. | Resources are used better because requests are checked carefully. |
| Example | Disallowing a process from holding one resource while requesting another. | Using the Banker’s Algorithm for Deadlock Avoidance to check if a resource request is safe. |
Challenges in Implementing Deadlock Avoidance
Although deadlock avoidance in OS is highly useful, it may be challenging to apply in real systems. The operating systems have some difficulties that make their use more difficult.
1. Monitoring All Resources and Processes: It takes a longer time to check whether each resource request keeps the system in a safe state. It can also slow down the system when too many requests come at once.
2. High Processing Overhead: It takes a longer time to check whether each request for the system is in a safe state or not. This can slow down the system when many requests appear at once.
3. Changing Resource Needs: Processes in real systems can vary in the number of resources they require during execution. It is difficult for the operating system to update the deadlock avoidance algorithm rapidly.
4. Complexity in Large Systems: In a system having many users and resources, applying the banker’s algorithm for avoiding deadlock is complex. The OS must perform many checks, which can make the system slow.
Applications of Deadlock Avoidance in Modern Systems
Deadlock avoidance in operating systems is widely used today in different fields where safe and smooth processing is important.
1. Operating Systems: The modern OSs can use deadlock avoidance algorithms to handle processes and ensure they do not become stuck as they wait to get access to shared resources.
2. Database Management Systems: The databases apply deadlock avoidance methods to ensure that various users can access and update information safely at the same time without blocking one another.
3. Cloud Computing: Cloud systems have numerous users sharing the same resources. OS deadlock avoidance is used to ensure that these shared systems remain safe and no user tasks are stuck.
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Advantages and Disadvantages of Deadlock Avoidance
Below are the advantages and disadvantages of deadlock avoidance exaplained in detail:
Advantages
1. Avoids Deadlocks Before They Occur: The most significant advantage of deadlock avoidance in an OS is that it prevents deadlocks before they may take place.
2. Ensures System Safety: It ensures that all the processes can complete without problems by maintaining the system in a safe state.
3. Better Resource Use: Deadlock avoidance algorithms are flexible in the sharing of resources, hence the resources are used efficiently.
4. Increases System Stability: The system is more reliable since deadlocks are avoided and therefore runs smoothly.
Disadvantages
1. Requires Extra Data and Time: The system should continue to monitor the safe state and capture information regarding all the resources and processes, which adds workload.
2. Not Practical in All Large Systems: The deadlock-avoiding algorithm used by the banker may be slow and difficult to control in very large systems.
3. Highest Needs that are Hard to Predict: The number of resources required by any process is not always known, and thus, it is not always possible to use the algorithm accordingly.
4. Needs a Continuous Observation: It requires additional processing power because the system will need to continue checking on safe states after every period.
Best Practices for Deadlock Avoidance
Check Safe State regularly: Ensure that before providing new resources to a process, there is a verification of whether the system is in a safe state or not. This ensures that the system is maintained and not in a deadlock.
- Use the Banker Algorithm with Caution: One of the most commonly used methods of ensuring safety is the Banker’s Algorithm for Deadlock avoidance in an Operating System. Properly use it to determine whether or not a request in a process is safe.
- Monitor Resource Usage: Monitor the availability, utilization, and demands of the resources. Periodic monitoring assists the OS in identifying unsafe states in time.
- Set Maximum Resource Limits: Request each process to specify what its maximum resource requirement is. This aids the OS in planning and distributing resources securely.
- Focus on Important Processes: While checking for deadlocks, give priority to the important processes
- Test and Update Regularly: Testing helps in ensuring that the deadlock avoidance algorithm still works as new applications or updates are added to the system.
Conclusion
Deadlock avoidance in operating systems is very important to ensure that the systems are safe and stable by getting the resources that they need without getting stuck. The approaches, such as the Banker algorithm of Deadlock avoidance in OS, ensure that the system remains in a secure state. Although it would need additional checking and monitoring, the benefits are significant. This helps in maintaining smooth system performance and prevents unexpected crashes.
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Deadlock Avoidance in OS (Operating System) – FAQs
Q1. Why is deadlock avoidance important in an OS?
It helps the system run smoothly by preventing the processes from getting stuck.
Q2. How does the Banker’s Algorithm help in deadlock avoidance?
It makes sure that a process can get resources without stopping the other processes.
Q3. What is a safe state in deadlock avoidance?
A safe state is when all processes can finish without causing a deadlock.
Q4. What is the difference between deadlock prevention and deadlock avoidance?
Deadlock prevention tries to stop deadlocks before they can happen, while the deadlock avoidance carefully checks each request to make sure it will not cause a deadlock.
Q5. Where is deadlock avoidance used in real systems?
It is used in operating systems, databases, and cloud computing for managing the resources safely.