Operating Systems 3 - Process Manager Part 2

Summary

This video explains the key aspects of scheduling policies and resource management in operating systems. It covers the challenges of resource limitations, deadlocks, starvation, and synchronization, as well as various job scheduling algorithms like FCFS, SJN, and round robin. The video highlights the importance of balancing fairness, throughput, and CPU efficiency, while also preventing resource hogging. It also introduces concepts like preemptive and non-preemptive schedulers, time quantum, and multi-level queues. Finally, it touches upon synchronization issues such as deadlock, livelock, and starvation, setting the stage for deeper discussions on device management in the next tutorial.

Takeaways

• 😀 A scheduling policy is needed when managing many jobs or limited resources, addressing system limitations like finite resources, locked resources, and job reassignment.
• 😀 The goal of a scheduling policy is to maximize throughput, provide quicker responses, ensure fairness, and maintain efficient CPU service, avoiding resource hogging.
• 😀 Resource hogging refers to a job monopolizing resources, requiring intervention to ensure proper resource allocation for all jobs.
• 😀 Scheduling policies are categorized into preemptive and nonpreemptive schedulers, with preemptive allowing interruptions of jobs and nonpreemptive requiring job completion before acting.
• 😀 The First-Come, First-Serve (FCFS) algorithm is nonpreemptive and handles jobs in the order they arrive, but may not work well in interactive systems due to unpredictable response times.
• 😀 Shortest Job Next (SJN) is another nonpreemptive algorithm, processing the smallest jobs first, but it needs accurate runtime estimates for effectiveness.
• 😀 Priority Scheduling is a nonpreemptive algorithm that prioritizes jobs based on predefined factors like job type and required resources.
• 😀 Shortest Remaining Time (SRT) is a preemptive version of SJN that allows interrupting longer jobs in favor of shorter ones, improving response times.
• 😀 Round Robin is a preemptive scheduling algorithm used in interactive systems, where each job is given a time slice (Time Quantum) to ensure equal CPU sharing.
• 😀 Multi-Level Queues use multiple queues with different scheduling policies, benefiting from various algorithms based on priority and job requirements.
• 😀 Synchronization between processes is essential to avoid issues like deadlock (no process releasing resources), livelock (resources are released but immediately re-locked), and starvation (one process monopolizing resources).

Q & A

What are the three main limitations of the system mentioned in the transcript?

The three main limitations are: finite resources (e.g., disk drives or printers), locked resources that cannot be shared, and the need for users to reassign jobs to optimize resource usage.

What is the primary goal of a scheduling policy in an operating system?

The primary goals are to maximize throughput, provide faster response times, ensure fairness for all jobs, and prevent resource hogging where one job monopolizes the resources.

What is the difference between preemptive and nonpreemptive scheduling?

Preemptive scheduling allows a job to be interrupted to give resources to another job, while nonpreemptive scheduling requires a job to complete before another job can take its place.

How does the FCFS (First Come, First Served) scheduling algorithm work?

FCFS is a nonpreemptive algorithm that executes jobs in the order they arrive. However, this approach can result in long waiting times, especially in interactive systems.

What is the issue with using FCFS in interactive systems?

FCFS can be problematic in interactive systems because it doesn't account for the different lengths of jobs, leading to unpredictable response times and inefficient handling of multiple jobs.

How does the SJN (Shortest Job Next) algorithm function?

SJN is a nonpreemptive algorithm that processes the shortest jobs first, but it requires knowledge of job runtimes beforehand. It prioritizes efficiency by minimizing the overall job completion time.

What is the difference between SJN and SRT (Shortest Remaining Time)?

SJN is nonpreemptive and processes the shortest job first, while SRT is a preemptive version of SJN, meaning it can interrupt a job to favor a shorter job if it is waiting.

What is the Round Robin scheduling algorithm, and how does it work?

Round Robin is a preemptive scheduling algorithm that allocates a fixed time slice (Time Quantum) to each job, ensuring that the CPU time is shared equally among all jobs. Once a job's time slice expires, it is placed back in the queue.

What are multi-level queues, and how do they benefit scheduling?

Multi-level queues are not a scheduling algorithm themselves, but they combine multiple scheduling policies into one system, each queue handling a different priority or policy, which allows for more flexible and efficient resource management.

What are the main synchronization issues that can arise in an operating system?

The main synchronization issues are deadlock (where processes are stuck and unable to release resources), livelock (where processes continuously release and acquire resources but never make progress), and starvation (where some processes are consistently denied resources).

How does deadlock differ from livelock in terms of system behavior?

Deadlock occurs when processes are unable to release resources, leading to a completely halted system. Livelock, on the other hand, involves processes that continuously release and reacquire resources but never actually make any progress.