Solutions to Critical Section Problem

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Questions and Answers

What is the primary difference between non-preemptive and preemptive scheduling?

Non-preemptive scheduling does not allow the CPU to be taken away from its currently executing process. (correct)
Non-preemptive scheduling is used for real-time systems.
Preemptive scheduling does not allow for process prioritization.
Non-preemptive scheduling allows for multiple processes to execute simultaneously.

What is the goal of maximizing CPU utilization?

To keep the CPU busy doing useful work at all times. (correct)
To ensure fairness in process execution.
To reduce the time it takes for a process to finish executing.
To minimize the time a process spends in the ready queue.

What is the First-Come, First-Served Algorithm (FCFS)?

A non-preemptive scheduling algorithm that executes processes in the order they arrive. (correct)
A scheduling algorithm that allocates fixed time slices to each process.
A preemptive scheduling algorithm that prioritizes processes based on their priority.
A real-time scheduling algorithm that guarantees process execution within a deadline.

What is the primary goal of minimizing response time?

To minimize the time between the submission of a request and the start of the system’s first response. (A) Signup and view all the answers

What is the primary goal of maximizing throughput?

To maximize the amount of work done by the CPU. (D) Signup and view all the answers

What is the primary goal of minimizing turnaround time?

To minimize the time between the point a process is submitted and the time it finishes executing. (B) Signup and view all the answers

What is the main characteristic of the Shortest Process First Algorithm?

It executes the process with the shortest CPU burst time first (A) Signup and view all the answers

What happens in the Shortest Remaining Time First Algorithm when a process with a shorter CPU burst time arrives in the ready queue?

The currently executing process is preempted (A) Signup and view all the answers

What is the main difference between the Round Robin Algorithm and the First-Come-First-Served Algorithm?

The Round Robin Algorithm assigns a time limit to each process (A) Signup and view all the answers

What is the main goal of the Priority Scheduling algorithm?

To execute the process with the highest priority first (B) Signup and view all the answers

What is the main characteristic of the Multilevel Feedback Queues algorithm?

It permanently assigns processes to a queue on entry to the system (C) Signup and view all the answers

What problem might occur when two or more processes or threads are updated simultaneously?

Problems might occur (D) Signup and view all the answers

What is the primary issue with software solutions to the critical section problem?

Busy waiting (D) Signup and view all the answers

Which hardware solution enables a process to modify a variable or memory location atomically?

Special hardware instruction (A) Signup and view all the answers

What is the purpose of a semaphore in process synchronization?

To solve complex synchronization problems (C) Signup and view all the answers

What does the Dining Philosophers Problem represent?

Use of limited resources (A) Signup and view all the answers

What is a deadlock situation in process management?

Two or more processes waiting for resources held by each other (B) Signup and view all the answers

What is the primary difference between readers and writers in the Readers and Writers Problem?

Readers can only read data, while writers can modify or update data (A) Signup and view all the answers

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Study Notes

CPU Scheduling

Non-Preemptive scheduling: CPU cannot be taken away from currently executing process
Preemptive scheduling: CPU can be taken away from currently executing process due to interrupt, higher priority process, or time limit exceeded

Performance Criteria for Schedulers

CPU utilization: maximize CPU busy time
Throughput: maximize work done by CPU
Turnaround time: minimize time between process submission and completion
Response time: minimize time between request submission and first response
Waiting time: minimize time spent in ready queue
Fairness: equal opportunity for all processes to use CPU

CPU Scheduling Algorithms

First-Come, First-Served Algorithm (FCFS): non-preemptive, execute processes in order of arrival
Shortest Process First Algorithm (SPF)/Shortest Job First Algorithm (SJF): non-preemptive, execute shortest CPU burst time first
Shortest Remaining Time First Algorithm (SRTF): preemptive, execute shortest remaining CPU burst time first
Round Robin Algorithm (RR): preemptive, execute in order of arrival with time limit (time quantum or time slice)
Priority Scheduling: execute highest priority process, may be non-preemptive or preemptive
Multilevel Feedback Queues: determine behavior pattern, permanently assign processes to queues

Process Synchronization

Bakery Algorithm: assigns smallest number to processes, allowing entry to critical section
Busy waiting: main problem with software solutions, stuck in while loop

Hardware Solutions to Critical Section Problem

Disabling interrupts: disable interrupts before modifying shared variables
Special hardware instruction: modify variables or memory locations atomically

Semaphore

Special integer variable protected by atomic operations
Solves complex synchronization problems without busy waiting

Classic Synchronization Problems

Dining Philosophers Problem: represents processes using limited resources
Deadlock: situation where two or more processes wait for resources held by each other
Readers and Writers Problem: represents access to database, readers examine data, writers modify data

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