Question

A process that is waiting for a time slice is said to suffer starvation if it is never given a time slice. a. The pavement in the middle of an intersection can be considered as a nonshareable resource for which cars approaching the intersection compete. A traffic light rather than an operating system is used to control the allocation of the resource. If the light is able to sense the amount of traffic arriving from each direction and is programmed to give the green light to the heavier traffic, the lighter traffic might suffer from starvation. How is starvation avoided? b. In what sense can a process starve if the dispatcher always assigns time slices according to a priority system in which the priority of each process remains fixed? (Hint: What is the priority of the process that just completed its time slice in comparison to the processes that are waiting, and consequently, which routine gets the next time slice?) How, would you guess, do many operating systems avoid this problem?

Short answer

Starvation in traffic or processes is avoided by ensuring fairness, like implementing policies for lighter traffic and priority aging for processes.

Step-by-step solution

Understanding Starvation in Traffic Systems

In part (a), the scenario described involves traffic lights managing cars as they approach an intersection. If the light prioritizes the heavier traffic flow, the lighter traffic could effectively face indefinite waiting times, leading to starvation. Starvation is avoided in this context by implementing a fairness policy—such as occasionally giving the green light to lighter traffic regardless of volume—ensuring all traffic gets a chance to move.

Analyzing Starvation in Priority-Based Scheduling

Part (b) examines how processes might starve under a fixed-priority system within an operating system. If priorities are fixed, a process with lower priority can indefinitely wait for a time slice as higher priority processes continuously preempt it. This is termed as starvation, where the waiting process never gets CPU time because newly arriving higher-priority requests keep preempting it.

Solution to Process Starvation

Operating systems often mitigate process starvation by implementing techniques such as "priority aging," where the priority of a waiting process is gradually increased the longer it waits, eventually allowing it to gain priority over newer arrivals. Alternatively, some systems use a round-robin method within priority levels, ensuring all processes get a chance to execute.

Key concepts

Priority-Based Scheduling

Priority-based scheduling in operating systems is a strategy used to determine the sequence in which processes are given the CPU time they need to execute. Each process is assigned a priority level, and the process with the highest priority is selected first for CPU allocation. This can make the system efficient by ensuring that important tasks are completed quickly.

There are different types of priority-based scheduling:

• Static Priority Scheduling: Where priorities are assigned when a process is created and remain unchanged during execution.
• Dynamic Priority Scheduling: Where priorities can change based on the system state or process behavior.

While effective, priority-based scheduling can lead to challenges if not managed well. One significant issue is process starvation, where lower priority tasks may never get the CPU time they need if higher priority tasks are always arriving.

Process Starvation

Process starvation occurs when a process is perpetually overlooked due to the scheduling policy, often found in systems using priority-based scheduling. It happens when a process waits in the queue indefinitely because other processes with higher priorities continue to be scheduled first.

To imagine this, think of being in a long line waiting for service, but new people keep jumping the line. Eventually, it feels like you'll never get served!

• Lower priority tasks might face long waits and delay.
• Starvation can lead to system inefficiencies and decreased performance.

To combat process starvation, operating systems can incorporate mechanisms such as priority aging or can use a hybrid scheduling strategy to ensure fairness across processes.

Traffic Light Fairness Policy

In non-computer systems like traffic management, a fairness policy ensures every direction of traffic gets a fair share of green light time, so vehicles don’t starve at intersections. This is similar to preventing process starvation in computing systems.

Traffic lights use sensors to detect the flow of traffic and manage intersection control. Without fairness policies, lighter traffic directions could be neglected indefinitely if the lights prioritize heavier flows continuously.


By implementing a fairness policy, lights may:

• Allow lighter traffic a turn regardless of flow.
• Rotate green lights in a predictable pattern to ensure no direction faces indefinite waits.

This concept highlights the importance of equitable resource distribution, a concept shared with operating systems managing process queues.

Resource Allocation

Resource allocation in operating systems is the process by which system resources like CPU time, memory, and I/O are distributed among processes and tasks. The goal is to optimize performance while ensuring fairness and preventing issues like starvation.

Operating systems must carefully manage resources to maintain optimal performance:

• Allocate resources dynamically according to system needs and process priority.
• Implement algorithms to keep track of system resource usage and adjust priorities.

These steps help maintain balance, ensuring that every process gets the necessary resources without one monopolizing everything. Effective resource allocation minimizes latency and maximizes system throughput, enhancing overall efficiency.

Priority Aging

Priority aging is a technique used to prevent starvation in priority-based scheduling systems. It gradually increases the priority of a process the longer it waits in the queue. By doing this, even low-priority processes eventually get their turn at execution, preventing indefinite waiting.

Imagine being bumped up a line if you've waited long enough, ensuring everyone gets served eventually.

• Priority is incremented over time for processes in the waitlist.
• This method ensures a balance between new and waiting processes.

Priority aging is crucial in maintaining system fairness, particularly in systems where process demands and load can vary widely. Through this technique, systems can handle processes dynamically while minimizing starvation risk.