Question

What do you understand by Circular wait? Is it possible to create a deadlock using only the Mutual exclusion? Explain in your own way.

Answer 1

Q) What do you understand by Circular wait?

Ans: Circular wait: each process must be waiting for a resource which is being held by another process, which in turn is waiting for the first process to release the resource.

Q) Is it possible to create a deadlock using only the Mutual exclusion?

Ans: No, it is not possible to create a deadlock using only the Mutual exclusion condition.

A deadlock situation on a resource can arise if and only if all of the following conditions hold simultaneously in a system:

1. Mutual exclusion: At least one resource must be held in a non-shareable mode. Otherwise, the processes would not be prevented from using the resource when necessary. Only one process can use the resource at any given instant of time.^[6]
2. Hold and wait or resource holding: a process is currently holding at least one resource and requesting additional resources which are being held by other processes.
3. No preemption: a resource can be released only voluntarily by the process holding it.
4. Circular wait: each process must be waiting for a resource which is being held by another process, which in turn is waiting for the first process to release the resource. In general, there is a set of waiting processes, P = {P₁, P₂, …, P_N}, such that P₁ is waiting for a resource held by P₂, P₂ is waiting for a resource held by P₃ and so on until P_N is waiting for a resource held by P₁.^[3][7]

These four conditions are known as the Coffman conditions from their first description in a 1971 article by Edward G. Coffman, Jr.

Thus all of the conditions are necessary for a deadlock to occur because even with one condition missing, some of the resources can be successfully passed to the processes to execute either partially or completely so for complete deadlock to occur, we need all the 4 conditions to take place simultaneously, so that every process keeps waiting for its corresponding resource for its execution.

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