Two marks Questions with Answers

Two Marks Questions with Answers

Q.1 What is a deadlock ?

Ans. A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause. Usually the event is release of a currently held resource.

Q.2 State the conditions for deadlock.

Four conditions for deadlocks are:

Ans. :

a. Mutual exclusion

b. Hold and wait

c. No preemption

d. Circular wait

1. Atleast one resource must be held in a nonsharable mode.

2. A process holding atleast one resource is waiting for more resources held by other processes.

3.Resources cannot be preempted.

4.There must be a circular waiting.

Q.3 What is deadlock state ?

Ans. If there is any process deadlock in a state, then that state is called deadlock

state.

Q.4 What is resource-allocation graph ?

Ans. Deadlocks can be described more precisely in terms of a directed graph called a system resource-allocation graph.

Q.5 Is it possible to have a deadlock involving only one process? State your

answer.

Ans. No. This follows directly from the hold-and-wait condition.

Q.6 List two examples of deadlocks that are not related to a computer system environment.

Ans. a. Two cars crossing a single-lane bridge from opposite directions.

b. A person going down a ladder while another person is climbing up the ladder:

Q7. Define safe state.

Ans.  A state is safe if the system can allocate resources to each process (up to its maximum) in some order and still avoid a deadlock.

Q.8 When is a set of processes deadlocked ?

Ans. Resource deadlock : Each process requests resources held by another process in the set and it must receive all the requested resources before it can become unblocked. Communication deadlock: Each process is waiting for communication from another process and will not communicate until it receives the communication for which it is waiting.

Q.9 Define request edge and assignment edge.

Ans. There is a request edge from process P to resource R if and only if P is blocked waiting for an allocation of R. There is an assignment edge from resource R to process P if and only if P is holding an allocation of R.

Q.10 What is hold and wait?

Ans. Hold and Wait : A process must be holding a resource and waiting for another.

Q.11 What is a knot ?

Ans. A strongly connected sub-graph of a directed graph, such that starting from any node in the subset it is impossible to leave the knot by following the edges of the graph.

Q.12 What is banker's algorithm ?

Ans. Banker's algorithm is a deadlock avoidance algorithm that is applicable to a resource-allocation system with multiple instances of each resource type.

Q.13 Which are two options to break a deadlock ?

Ans. There are two options for breaking a deadlock :

1. Process termination: To abort one or more processes to break the circular wait.

2. Resource preemption: To preempt some resources from one or more of deadlock

Q.14 Write the three ways to deal the deadlock program.

Ans. Three ways to deal with the deadlock problem :

1. Use a protocol to prevent or avoid deadlocks, ensuring that the system will never enter a deadlock state.

2. Allow the system to enter a deadlock state, detect it and recover.

3. Ignore the problem altogether and pretend that deadlocks never occur in the system.

Q.15 List out the methods used to recover from the deadlock.