GO Classes DPP | OS | DEADLOCK

Answer 1

1. Deadlock Analysis: Is it Deadlock-Free?

For a deadlock to occur, we must be able to form a Circular Wait. Let's test if a cycle can be created using Rule 1 (the only rule that allows a process to wait):

• Rule 1 states: $P_r$ waits for $P_h$ only if $\operatorname{Pri}\left(P_r\right)>\operatorname{Pri}\left(P_h\right)$.
   
• Suppose we have a chain: $P_1$ waits for $P_2, P_2$ waits for $P_3$, and $P_3$ waits for $P_1$.
   
• According to the rule, this requires: $\operatorname{Pri}\left(P_1\right)>\operatorname{Pri}\left(P_2\right)>\operatorname{Pri}\left(P_3\right)>\operatorname{Pri}\left(P_1\right)$.
   
• This is mathematically impossible $\left(\operatorname{Pri}\left(P_1\right)>\operatorname{Pri}\left(P_1\right)\right.$ is a contradiction).

Because the "Wait" condition is based on a strict ordering of priorities, a cycle can never form. If Rule 2 triggers, a process is killed, which breaks any potential hold-and-wait chain.
 

Result: The scheme is DEADLOCK-FREE.



2. Starvation Analysis: Is it Starvation-Free?

Starvation occurs if a process can be killed infinitely many times without ever completing. Let's look at the "Restart" mechanic:

• When a process is killed, it keeps its original Timestamp and its Priority increases.
   
• The Priority Boost: Since priority increases every time a process is killed, $\operatorname{Pri}\left(P_r\right)$ will eventually become higher than any other $\operatorname{Pri}\left(P_h\right)$ in the system. Once it is the highest priority, Rule 1 triggers, and it is allowed to Wait instead of being killed.
   
• The Timestamp Protection: Even if it hasn't reached the highest priority yet, its original (old) timestamp helps it in Rule 2. As the oldest process ( $T\left(P_r\right)$ is smallest), it would kill $P_h$ rather than being killed itself.
   

Since every time a process "fails," it returns stronger (higher priority) or older relative to new processes, it is guaranteed to eventually acquire the resource.
 

Result: The scheme is STARVATION-FREE.

Answer 2

The best way to solve these kind of questions is ask yourself four questions:

1. Is the requested process force the process already holding the current resource. (Deadlock Freedom)

Here we see in case 2 exactly that happening.

2. Is there any one way edge like here we have a dependency as Younger -> Older (Deadlock Freedom)

3. Is the aborted process priority or the checking condition may get increasing continuously without getting back to its original value.(Starvation Free) .Yes that's exactly happening in case 2.

4. Can a process repeatedly posponed (Stravation Hurts)

HENCE (C) is the answer