SUJALADITZ
OPERATING SYSTEM QUESTION AND ANSWERS:-
Answer any five questions (5 x 2 = 10)
1. Define Deadlock
A deadlock is a situation in a multi-process system where two or more processes are unable to proceed because each is waiting for a resource held by another, forming a cycle of dependencies.
2. Define Critical Section
A critical section is a part of a program where shared resources are accessed and modified, and which must be executed by only one process or thread at a time to avoid race conditions.
3. Define Logical Address and Physical Address
Logical Address:
A virtual address generated by the CPU during program execution, which does not correspond to a physical location in memory.
Physical Address:
The actual location in the main memory where data or instructions reside.
4. Define Swapping
Swapping is a memory management technique where a process is temporarily moved from main memory to secondary storage (disk) to free up space for other processes.
5. Define Race Condition
A race condition occurs when the behavior of software depends on the relative timing of events such as thread execution order, leading to unpredictable and erroneous results.
6. Define Monitor
A monitor is a synchronization construct that allows safe access to shared resources by ensuring that only one thread can execute a critical section at a time, using mechanisms like mutexes and condition variables.
7. List Different Methods of Handling Deadlock?
Deadlock Prevention: Altering system design to ensure at least one of the Coffman conditions for deadlock cannot occur.Deadlock Avoidance: Using algorithms like Banker's Algorithm to avoid unsafe states.Deadlock Detection and Recovery: Allowing deadlocks to occur, detecting them using techniques like resource allocation graphs, and recovering from them by terminating or rolling back processes.Answer any two questions (2 x 5 = 10)
1. Explain Dining Philosopher Problem of Synchronizing with Diagram
The Dining Philosopher Problem is a classic synchronization problem introduced by Edsger Dijkstra. It is used to illustrate the challenges of allocating limited resources among multiple processes without causing deadlocks.
Problem Description:- There are five philosophers sitting around a circular table.
- Each philosopher alternates between thinking and eating.
- There are five forks on the table, one between each pair of adjacent philosophers.
- A philosopher needs both adjacent forks to eat.
Challenges:- If every philosopher picks up the fork to their right at the same time, all of them will wait indefinitely, leading to a deadlock.
Solution:
To solve this problem, various synchronization techniques can be applied:- Resource Hierarchy Solution: Assign a unique number to each fork. Philosophers pick up the lower-numbered fork first and the higher-numbered fork second.
- Arbitrator Solution: Use a mediator (a waiter) who ensures that a philosopher can pick up both forks before starting to eat.
Diagram:
Philosopher 1
/ \
Fork1 Fork2
/ \
Philosopher 5 Philosopher 2
\ /
Fork5 Fork3
\ /
Philosopher 4
|
Fork4
|
Philosopher 3
2. Explain Deadlock Prevention
Deadlock prevention involves designing the system in such a way that at least one of the necessary conditions for deadlock (Coffman conditions) is violated. The Coffman conditions are:- Mutual Exclusion: Resources are held exclusively by one process.
- Hold and Wait: Processes holding resources can request additional resources.
- No Preemption: Resources cannot be forcibly taken away from processes.
- Circular Wait: A circular chain of processes exists, each waiting for a resource held by the next process in the chain.
Prevention Techniques:- Mutual Exclusion: Not applicable for resources that must be shared.
- Hold and Wait: Require processes to request all resources they need before starting execution.
- No Preemption: Allow the system to preempt resources from a process if it is waiting for others.
- Circular Wait: Impose a strict ordering of resources and ensure that each process requests resources in increasing order.
3. Explain Paging in Detail with Diagram
Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. This helps to avoid fragmentation and makes the use of memory more efficient.
How Paging Works:- Logical Address Space: Divided into fixed-size pages.
- Physical Address Space: Divided into fixed-size frames, each frame size is the same as the page size.
Translation Process:- The CPU generates a logical address.
- The logical address is divided into two parts: the page number and the offset.
- The page number is used to index into a page table.
- The page table contains the base address of each page in physical memory.
- The base address is added to the offset to get the physical address.
Diagram:
Logical Address:
Page Number | Offset
---------- ------
2 | 1024
Page Table:
Page Number | Frame Number
------------ ------------
0 | 5
1 | 8
2 | 12
Translation:
Page Number 2 -> Frame Number 12
Physical Address = 12 * Frame Size + Offset
Advantages:- Eliminates external fragmentation.
- Easy to allocate memory as any free frame can be used.
Disadvantages:- May suffer from internal fragmentation if processes don't fully use the allocated pages.
- Requires additional memory to store the page table.
4. Explain Deadlock Characterization
Deadlock Characterization refers to the conditions that must hold simultaneously for a deadlock to occur. These are known as the Coffman conditions:- Mutual Exclusion: Only one process can use a resource at a time.
- Hold and Wait: A process holding at least one resource is waiting to acquire additional resources held by other processes.
- No Preemption: Resources cannot be forcibly taken from a process; they must be released voluntarily.
- Circular Wait: A set of processes exists such that each process is waiting for a resource held by the next process in the set, forming a circular chain.
Example:- Process P1 holds Resource R1 and requests Resource R2.
- Process P2 holds Resource R2 and requests Resource R1.
- Both processes cannot proceed, leading to a deadlock.
Prevention Strategies:- Mutual Exclusion: Make resources sharable if possible.
- Hold and Wait: Require processes to request all resources at once.
- No Preemption: Allow the system to preempt resources if necessary.
- Circular Wait: Impose a linear ordering of resource types and ensure each process requests resources in an increasing order of enumeration.
These strategies aim to prevent the system from entering a deadlock state by ensuring that at least one of these conditions cannot hold.
EXAM OVER....
BEST OF LUCK GUYS.
CREATED AND PUBLISHED BY:-SUJAL.S.RAJAMANI.
