How unsafe state differs from deadlocked state? Consider follows initial state and identify wheather requested is and granted or denies for the given cases.

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Suresh Chand · Accepted Answer

If a system goes to an unsafe state, it may or may not go to a deadlock state. So, unsafe and deadlock states are different. An unsafe state implies that some unfortunate sequence of events might lead to deadlock. But, it is not entirely sure that the system will go to deadlock. Thus, Banker's algorithm is used to see if granting each resource requested leads to a safe state or not. If it leads, the request is granted, otherwise postponed. First, Let's make the column for needed resources. Process Need= Max - has A 4 B 4 C 1 D 5 Now, let's check the safe sequence using Banker's algorithm. i) For process A: Need Available 4 2 Since Need > Available; A is not executed. ii) For process B: Need Available 4 2 Since Need > Available; B is not executed. iii) For process C: Need Available 1 2 Since Available > Need; C is executed. New available = 2 + 2 = 4 iv) For process D: Need Available 5 4 Since Need > Available; D is not executed. iv) For process A: Need Available 4 4 Since Need = Available; A is executed. Now, available = 4 + 2 = 6 v) For process B: Need Available 5 6 Since Available > Need; B is executed. Now, available = 6 + 1 = 7 vi) For process D: Need Available 5 7 Since Available > Need; D is executed. Now, available = 7 + 3 = 10 Since it is in a safe state as all the processes are executed. So, the safe sequences . Hence, all the requested resource is granted. If D requests 1 resource: New available = 2 - 1 = 1 New need for D = 5 - 1 = 5 New allocation = D = 3 + 1 = 4 Process Has Need A 2 4 B 1 4 C 2 1 D 4 4 Available = 1 Now, again let's check the safe sequence For Process A, Need = 4 > Available =1 So, A is not execueted For Process B, Need = 4 > Available = 1. So, B is not executed For Process C, Need = 2 > Available = 1. So, C isn't executed For Process D, Need = 4 > Available = 1. So, D isn't executed Since none of the processes granted the request for resources. So, when D request 1, the System goes to deadlock. If A requests 1 resource: New available = 2 - 1 = 1 New need for A = 4 - 1 = 3 New allocation for A = 2 + 1 = 3 Let's check the safe sequence For process A, Need = 3 > Available = 1. So, A isn't executed. For process B, Need = 4 > Available = 1. So, B isn't executed For process C, (Need = 1) = (Available = 1) . So, C is executed and New available = 1 + 2 = 3 For process D, Need = 5 > Available = 3. so, D isn't executed For process A, (Need = 3) = (Available = 3). So, A is executed and New available = 3 + 3 = 6 For process B, Need = 4 < Available = 6. So, B is executed. New available = 6 + 1 = 7 For process D, Need = 5 < Available = 7. So, D is executed and New available = 7 + 3 = 10 Since all the requested resources are granted. So, the system is in a safe state and the safe sequence is

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