Chapter 5 & 7 (Quiz 5 Portion)

Question 1

What is the “Critical section” problem?

Answer 1

1- Process may be changing common variables, updating table, writing file, etc.
2- When one process in critical section, no other may be in its critical section.

Question 2

What are the solutions to Critical-Section problem?

Answer 2

1- Mutual Exclusion.
2- Progress.
3- Bounded Waiting.

Question 3

What is “Mutual Exclusion” ?

Answer 3

If process Pi is executing in its critical section, then no other processes can be executing in their critical sections.

Question 4

What is “Progress” ?

Answer 4

If no process is executing in its critical section and there exist some processes that wish to enter then cannot be postponed indefinitely.

Question 5

What is the difference between Preemptive & Non-preemptive kernel in Critical-Section Handling in OS?

Answer 5

1- Preemptive : allows preemption of process when running in kernel mode.

2- Non-preemptive : runs until exits kernel mode, blocks, or voluntarily yields CPU.

Question 6

Is there Critical-Section in Hardware? and why?

Answer 6

No, because of using locking.

Question 7

What is the difference between “Uniprocessors” & “Modern machines” ?

Answer 7

Uniprocessors : could disable interrupts.
Modern machines : Atomic = non-interruptible.

Question 8

What is “Semaphore”?

Answer 8

Synchronization tool that provides more sophisticated ways (than Mutex locks) for process to synchronize their activities.

Question 9

What is “Starvation” in Process Synchronization?

Answer 9

A process may never be removed from the semaphore queue in which it is suspended.

Question 10

What is “Priority Inversion”?

Answer 10

Scheduling problem when lower-priority process holds a lock needed by higher-priority process.

Question 11

What are the Classical Problems of Synchronization?

Answer 11

1- Bounded-Buffer Problem.
2- Readers and Writers Problem.
3- Dining-Philosophers Problem.

Question 12

What is the Readers and Writers Problem?

Answer 12

Allow multiple readers to read at the same time.

Question 13

What is the Solution to the Readers and Writers Problem?

Answer 13

Using Priorities.

Question 14

How does a process utilizes a resource?

Answer 14

1- Request.
2- Use.
3- Release.

Question 15

What are the Deadlock Characterization?

Answer 15

1- Mutual exclusion.
2- Hold and wait.
3- No preemption.
4- Circular wait.

Question 16

What is the “Mutual exclusion” from Deadlock Characterization?

Answer 16

Only one process at a time can use a resource.

Question 17

What is the “Hold and wait” from Deadlock Characterization?

Answer 17

A process holding at least one resource is waiting to acquire additional resources held by other processes.

Question 18

What is the “No preemption” from Deadlock Characterization?

Answer 18

A resource can be released only voluntarily by the process holding it, after that process has completed its task.

Question 19

What happens if Resource allocator graph contains no cycles?

Answer 19

No deadlock.

Question 20

What happens if Resource allocator graph contains a cycle?

Answer 20

1- If only one instance per resource type, then deadlock.
2- If several instances per resource type, possibility of deadlock.

Question 21

What is the “Mutual Exclusion” from the deadlock prevention?

Answer 21

Not required for sharable resources (read-only files).

Question 22

What is the “Hold and wait” from the deadlock prevention?

Answer 22

Must guarantee that whenever a process requests a resource, it does not hold any other resources.

Question 23

What is the “No preemption” from the deadlock prevention?

Answer 23

If a process that is holding some resources requests another resource that cannot be immediately allocated.

Question 24

What is the “Circular wait” from the deadlock prevention?

Answer 24

Impose a total ordering of all resource types.

Question 25

What happens if a system is in a safe state?

Answer 25

No deadlock.

Question 26

What happens if a system is in a unsafe state?

Answer 26

Possibility of deadlock.

Question 27

What is “Avoidance”?

Answer 27

Ensure that a system will never enter an unsafe state.

Question 28

What are the points for Recovery from Deadlock?

Answer 28

1- Process Termination.
2- Resource preemption.

Question 29

What is the “Process Termination” in Recovery from Deadlock?

Answer 29

1- Abort all deadlocked processes.
2- Abort one process at a time until the deadlock cycle is eliminated.

Question 30

In which order should we choose to abort? (Mention at least 5)

Answer 30

1- Priority of the process.
2- How long process has computed, and how much longer to completion.
3- Resources the process has used.
4- Resources process needs to complete.
5- How many processes will need to be terminated.
6- Is process interactive or batch?.

Question 31

What is the “Selecting a victim” from Resource Preemption?

Answer 31

Minimize cost.

Question 32

What is the “Rollback” from Resource Preemption?

Answer 32

Return to some safe state, restart process for that state.

Question 33

What is the “Starvation” from Resource Preemption?

Answer 33

Same process may always be picked as victim.