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GO Classes DPP | GATE CS | Operating System | Wait-For Graph

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In the wait-for graph for transactions $A$ through $G$ shown below, which option lists all transactions that are in a permanent waiting state?

Here, an edge $X \to Y$ in the wait-for graph means that transaction $X$ is waiting for a resource locked by transaction $Y$ to be unlocked.

Wait-for graph for transactions $A$–$G$:

Which of the following is correct?

  1. $A,\ B,\ C,\ D$
     
  2. $B,\ C,\ D$
     
  3. $B,\ C,\ D,\ F$
     
  4. $C,\ D,\ E,\ F,\ G$

1 Answer

1 1 vote

First identify a cycle:

$B\rightarrow D$

$D\rightarrow C$

$C\rightarrow B$

So, $\boxed{B\rightarrow D\rightarrow C\rightarrow B}$ is a wait-for cycle.

Hence, $B,C,D$ are deadlocked.

Now examine $F$.

$F$ waits for $D$ as well as $E$.

Since $D$ is part of the deadlocked cycle, it will never release the required resource.

Therefore $F$ also waits permanently, even though $F$ itself does not belong to the cycle.

So the permanently waiting set is $\boxed{{B,C,D,F}}$
 

Answer : C

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