Deadlock prevention in OS is a proactive approach employed by operating systems to eliminate or avoid the formation of deadlocks altogether. It aims to break the necessary conditions for deadlocks to occur. Various strategies are used to prevent deadlocks, and they include:

Resource Allocation Denial: The operating system carefully analyzes resource requests from processes and denies a request if granting it would result in a deadlock.

Resource Ordering: This strategy involves imposing a total ordering of all resource types and requiring that each process requests resources in an increasing order of enumeration.

Hold and Wait Prevention: This technique aims to prevent a process from holding resources while waiting for others by requiring a process to request and be allocated all its resources before it begins execution.

Preemptive Resource Allocation: In this approach, the operating system can preempt resources from a process when necessary, breaking the hold and wait condition.

Spooling/I/O Scheduling: This strategy involves using spooling or I/O scheduling to prevent deadlocks by ensuring that processes do not block each other when accessing I/O devices.

These strategies aim to ensure that all requests are safe by eliminating at least one of the four necessary conditions for deadlock, which are mutual exclusion, hold and wait, no preemption, and circular wait.

How does the hold and wait method prevent deadlocks?

The hold and wait method is a deadlock prevention technique that aims to prevent a process from holding resources while waiting for others by requiring a process to request and be allocated all its resources before it begins execution. This technique helps in breaking the hold and waits condition, which is one of the necessary conditions for deadlock.

By making to ensure that a process has all the resources it requires before it starts execution, the hold and waits method discards the possibility of the process holding a resource while waiting for another resource that can lead to a deadlock.

However, this technique can be inefficient as it may require a process to wait for resources it does not need immediately, leading to resource wastage. Therefore, it is essential to carefully analyze the resource requirements of each process and allocate resources efficiently to prevent deadlocks while minimizing resource wastage.

Difference between deadlock prevention and deadlock detection

Deadlock Prevention:

Deadlock prevention aims to prevent deadlocks from occurring by restricting the way resources are allocated. It involves blocking at least one of the four conditions necessary for deadlock to occur, which are mutual exclusion, hold and wait, no preemption, and circular wait.

This technique is simpler to implement as it relies on algorithms that restrict the way resources are allocated. However, it may lead to decreased system performance due to additional checks performed during resource allocation.

Deadlock Detection:

Deadlock detection involves examining the state of the system to determine whether a deadlock has occurred. It does not prevent deadlocks but rather identifies when a deadlock has already taken place. So, it is totally different from deadlock avoidance in OS.

Once a deadlock is detected, the system can take actions such as killing one or more processes involved in the deadlock or releasing some of the resources they hold to recover from the deadlock situation.