Question

Consider a computer system with multiple shared resource types, with one instance per resource type. Each instance can be owned by only one process at a time. Owning and freeing of resources are done by holding a global lock \(L\). The following scheme is used to own a resource instance: 

function OwnResource(Resource R) 
     Acquire lock L // a global lock 
     if R is available then 
          Acquire R 
          Release lock L 
     else 
          if R is owned by another process P then 
               Terminate P, after releasing all resources owned by P 
               Acquire R 
               Restart P 
               Release lock L 
          end if 
     end if 
end function

Which of the following choice(s) about the above scheme is/are correct? 
 

• A. The scheme ensures that deadlocks will not occur.
• B. The scheme may lead to live-lock.
• C. The scheme may lead to starvation.
• D. The scheme violates the mutual exclusion property.

Hint:

Deadlock avoidance through forced preemption can introduce live-lock and starvation if fairness is not ensured.

Answer 1

The Correct Option is A, B, C

Step 1: Analyze deadlock possibility.
Deadlock requires circular wait, hold-and-wait, mutual exclusion, and no preemption. In this scheme, if a process \(P\) holds a resource needed by another process, \(P\) is forcibly terminated and its resources are released. This introduces preemption. Hence, circular wait cannot persist.
Therefore, the scheme ensures that deadlocks will not occur. Option (A) is correct.

Step 2: Analyze possibility of live-lock.
Live-lock occurs when processes continuously change state but make no progress. Here, a process may repeatedly acquire a resource, get terminated by another process requesting the same resource, and then get restarted. Such repeated termination and restart cycles can prevent any process from making forward progress.
Hence, the scheme may lead to live-lock. Option (B) is correct.

Step 3: Analyze starvation.
Starvation occurs when a process is perpetually denied access to a resource. In this scheme, a process may be repeatedly terminated whenever it acquires a resource, due to higher-priority or frequently executing competing processes. Thus, it may never complete execution successfully.
Hence, the scheme may lead to starvation. Option (C) is correct.

Step 4: Mutual exclusion property.
Each resource instance can be owned by only one process at a time, and access is protected using the global lock \(L\). Hence, mutual exclusion is preserved.
Therefore, option (D) is incorrect.

Step 5: Conclusion.
The correct choices are (A), (B), and (C).

Final Answer: (A), (B), (C)