Difference between Deadlock Prevention and Deadlock Avoidance

Deadlock prevention and avoidance are crucial in operating systems because they help ensure that the system can continue to operate without being stuck in a deadlock. Deadlocks can cause a system-wide halt, leading to loss of data, system downtime, and reduced productivity. Therefore, it is essential to prevent or avoid deadlocks in a computer system to maintain its availability and reliability.

Key Areas Covered

• What is Deadlock?

• What is Deadlock Prevention?

• Advantages and Disadvantages of Deadlock Prevention

• What is Deadlock Avoidance?

• Advantages and Disadvantages of Deadlock Avoidance

• Comparison between Deadlock Prevention and Deadlock Avoidance

What is Deadlock?

Deadlock is a situation in a computer system where two or more processes are unable to proceed with their execution because they are waiting for each other to release the resources they hold. In other words, each process is waiting for a resource held by another process, which in turn is waiting for a resource held by the first process. This results in a circular dependency, where the processes are stuck in a state of waiting and cannot continue with their execution, leading to a system-wide halt. Deadlock is a common problem in operating systems that have multiple processes competing for shared resources.

What is Deadlock Prevention?

Deadlock prevention refers to the set of techniques and methods used to prevent a system from entering a state of deadlock. Deadlocks can cause a system to freeze or crash, and can be a serious issue in computer systems. Deadlock prevention involves designing a system in a way that ensures that deadlocks do not occur. We can be achieved this by implementing techniques such as -

• Resource ordering

• Resource allocation denial

• Timeouts

• Avoidance of hold-and-wait conditions

• Resource preemption

These techniques help to ensure that resources are allocated in a way that prevents circular waiting conditions from arising, which is the primary cause of deadlocks.

Advantages and Disadvantages of Deadlock Prevention

Advantages

• Deadlock prevention eliminates the possibility of deadlocks from occurring in the system, which ensures that the system can continue operating without interruption

• Deadlock prevention can improve system reliability by eliminating the possibility of deadlocks, which can lead to data loss or system crashes.

Disadvantages

• Deadlock prevention can be difficult to implement as it requires careful consideration of resource allocation and scheduling policies to avoid circular dependencies between processes.

• Deadlock prevention can lead to decreased system utilization, as it may require some resources to be kept idle to prevent deadlocks.

What is Deadlock Avoidance?

Deadlock avoidance is a technique used in operating systems to prevent the occurrence of deadlock. Deadlock avoidance involves analyzing the resource requirements of each process and making decisions about resource allocation to prevent potential deadlocks. This is done by predicting the possible resource needs of each process and allocating resources in a way that avoids the possibility of a deadlock.

There are several methods for deadlock avoidance in operating systems. These methods use different algorithms and techniques to predict whether granting a resource request would lead to a deadlock. The Banker's algorithm is the most widely used methods to avoid deadlock. Banker’s algorithm is a resource allocation algorithm that works by simulating the allocation of resources to processes and determining if it is possible to satisfy all requests without creating a deadlock. If a request cannot be granted without leading to a deadlock, it is not allowed.

Advantages and Disadvantages of Deadlock Avoidance

Advantages

• Deadlock avoidance can prevent deadlocks from occurring without limiting the functionality of the system. This means that the system can continue to operate normally without the risk of a deadlock.

• Deadlock avoidance can lead to better system performance as the system does not need to spend time resolving deadlocks.

Disadvantages

• Deadlock avoidance can be complex to implement as it requires the use of algorithms that analyse the resource allocation state of the system and predict whether granting a resource request would lead to a deadlock. This can require additional processing time and memory resources.

• Deadlock avoidance may require additional resources to be kept idle to ensure that the system can safely grant resource requests without causing a deadlock. This can lead to decreased system utilization.

Comparison between Deadlock Prevention and Deadlock Avoidance

Deadlock prevention and deadlock avoidance are two techniques used in operating systems to prevent the occurrence of deadlocks. While both techniques aim to prevent deadlocks, they differ in their approach and the methods used.

S.No	Factors	Deadlock prevention	Deadlock avoidance
1.	Approach	Deadlock prevention aims to prevent deadlocks from occurring by restricting the way resources are allocated.	Deadlock avoidance aims to prevent deadlocks by dynamically analysing the resource allocation state of the system and deciding whether a resource request should be granted or not.
2.	Resource utilization	Deadlock prevention can lead to lower resource utilization because it requires the system to allocate resources conservatively to avoid deadlocks.	Deadlock avoidance allows the system to allocate resources more freely, leading to higher resource utilization.
3.	Algorithm complexity	Deadlock prevention is often easier to implement because it relies on simpler algorithms that restrict the way resources are allocated.	Deadlock avoidance, on the other hand, requires more complex algorithms that analyse the resource allocation state of the system and predict the outcome of resource allocation.
4.	System performance	Deadlock prevention can lead to decreased system performance because it may require additional checks to be performed when resources are allocated	Deadlock avoidance can result in better system performance because it does not need to spend time resolving deadlocks.
5.	System flexibility	Deadlock prevention is less flexible because it restricts the way resources are allocated, which can be limiting in some situations.	Deadlock avoidance is more flexible than deadlock prevention because it allows the system to adapt to changes in the resource allocation state.
6.	Overhead	Deadlock prevention usually incurs less overhead than deadlock avoidance. This is because deadlock prevention techniques are usually implemented as part of the resource allocation algorithm.	Whereas deadlock avoidance techniques require additional checks to be performed at runtime.
7.	Advantage	Deadlock prevention eliminates the possibility of deadlocks from occurring in the system, which ensures that the system can continue operating without interruption.	Deadlock avoidance can prevent deadlocks from occurring without limiting the functionality of the system. This means that the system can continue to operate normally without the risk of a deadlock.
8.	Disadvantage	Deadlock prevention can lead to decreased system utilization, as it may require some resources to be kept idle to prevent deadlocks.	Deadlock avoidance may not be able to prevent all deadlocks in a system, particularly in cases where resource needs are unpredictable or the system is subject to changes in the resource allocation state.

Conclusion

The choice between deadlock prevention and deadlock avoidance depends on the specific needs of the system. Deadlock prevention is a good choice for systems with predictable resource needs and limited resource types, while deadlock avoidance is a good choice for systems with unpredictable resource needs and multiple resource types. Deadlock prevention is simpler to implement, while deadlock avoidance is more flexible and can result in higher resource utilization and better system performance.