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Define a deadlock ? Write down the conditions responsible for deadlock? How can we recover from deadlock ?

A deadlock is a situation in computer systems where two or more processes are blocked, and each process is waiting for another process to release a resource that it needs in order to proceed.

In other words, a deadlock occurs when two or more processes are stuck in a loop, waiting for each other to finish their work, and neither can proceed until the other finishes.

There are four necessary conditions for a deadlock to occur:

1. Mutual exclusion: At least one resource must be held in a non-sharable mode, meaning only one process can use it at a time.

2. Hold and Wait: A process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes.

3. No Preemption: Resources cannot be forcibly taken away from a process. A process must release its resources voluntarily.

4. Circular Wait: There must be a circular chain of two or more processes, each of which is waiting for a resource held by the next process in the chain.

To recover from a deadlock, there are several strategies that can be used:

1. Prevention: By designing the system in such a way that at least one of the four necessary conditions for a deadlock is not met, we can prevent deadlocks from occurring. For example, we can ensure that resources are not held for too long, or we can use preemption to take away resources from a process that has been waiting for a long time.

2. Detection and Recovery: If prevention is not possible or practical, we can use a deadlock detection algorithm to identify when a deadlock has occurred. Once a deadlock is detected, we can use recovery strategies such as killing one or more processes, rolling back the system to a previous state, or forcing processes to release resources.

3. Avoidance: A more proactive approach is to use a resource allocation algorithm that ensures that requests for resources do not lead to deadlocks. This can be done by maintaining a global state of the system and predicting whether a resource allocation will lead to a deadlock before granting the request.