PROGRAM MASTER OF COMPUTER APPLICATION SEMESTER II SUBJECT CODE & NAME MCA211 – OPERATING SYSTEM BK ID B1405 NUMBER OF ASSIGNMNETS, CREDITS & MARKS 2, 4 Credits,30 marks each

Q.3. Define Deadlock. Explain necessary conditions for deadlock.                                             2+8

Answer:-

Deadlock:-

Several processes compete for a finite set of resources in a multi programmed environment. A process requests for resources that may not be readily available at the time of the request. In such a case the process goes into a wait state. It may so happen that this process may never change state because the requested resources are held by other processes which themselves are waiting for additional resources and hence in a wait state. This situation is called a deadlock.

Necessary Conditions for Deadlock:-

A deadlock occurs in a system if the following four conditions hold simultaneously:

1) Mutual exclusion: At least one of the resources is non-sharable, that is, only one process at a time can use the resource. 

2) Hold and wait: A process exists that is holding on to at least one resource and waiting for an additional resource held by another process. 

3) No pre-emption: Resources cannot be pre-empted, that is, a resource is released only by the process that is holding it.

4) Circular wait: There exist a set of processes P₀, P₁… P_n of waiting processes such that P₀ is waiting for a resource held by P₁, P₁ is waiting for a resource held by P₂… P_n-1 is waiting for a resource held P_n and P_n is in turn waiting for a resource held by P₀.

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