Last Updated on July 28, 2023 by Mayank Dham
In the world of operating systems, efficiency and fairness in resource allocation are critical factors that impact the overall system performance and user experience. However, in complex multi-process environments, there is a phenomenon known as "Starvation" that can significantly affect the system’s behavior and hinder its optimal functioning.
Starvation occurs when a process or a thread is perpetually deprived of the resources it needs to execute, leading to its prolonged or indefinite wait. This unfortunate situation arises when certain processes, often referred to as "starved processes," are unable to acquire the required resources due to the presence of other higher-priority processes or scheduling algorithms that prioritize certain tasks over others.
What is Starvation in Operating Systems?
Starvation in operating systems refers to a situation where a process or a thread is unable to make progress or execute its task due to a lack of essential resources, such as CPU time, memory, or I/O operations. It occurs when other processes or threads with higher priority continuously occupy or monopolize the necessary resources, preventing the starved process from getting its fair share of resources.
Starvation can lead to significant performance issues and impact the overall system’s responsiveness and efficiency. When a process is starved, it remains in a waiting state indefinitely, unable to complete its designated task or computation. This not only affects the starved process’s performance but may also cause delays or inefficiencies in other related processes, leading to a cascading effect on the entire system.
The occurrence of starvation can be attributed to various factors, such as improper resource allocation policies, priority inversion, or scheduling algorithms that favor specific processes over others. In multi-process environments, the challenge lies in maintaining a balance between fair resource allocation and meeting the needs of high-priority tasks without neglecting lower-priority ones.
Usually, when a process is delayed for an endless amount of time, starvation results. Resources required for the operating system to respond to process requests:
- CPU time
- Disk space
- network bandwidth
- I/O access to a network or disc
What Causes Starvation in OS?
Starvation in operating systems can be caused by various factors and situations. Some of the common causes of starvation are:
- Priority Inversion: Priority inversion occurs when a low-priority task is holding a resource that a high-priority task needs. As a result, the high-priority task cannot proceed until the low-priority task releases the resource. This situation can lead to the high-priority task being starved for an extended period, impacting its execution.
- Priority-Based Scheduling: Some scheduling algorithms in operating systems, such as priority-based scheduling, can prioritize certain processes over others based on their priority levels. If there are processes with very low priorities or continuously arriving high-priority tasks, lower-priority tasks may be starved and struggle to get CPU time.
- Resource Mismanagement: Inefficient resource management can lead to starvation. For example, if a process requires a specific resource, and other processes are continuously utilizing that resource without giving it up, the starved process will not get access to the required resource.
- Deadlock: In certain cases of deadlock, multiple processes are stuck in a circular wait, where each process is waiting for a resource held by another process. This can lead to starvation of these processes as they remain indefinitely blocked.
- Priority Aging: Priority aging is a technique used to mitigate the effects of priority inversion. By periodically boosting the priority of waiting processes, priority aging prevents long-term starvation and ensures that lower-priority tasks get a chance to execute.
- Overload: When a system is overloaded with too many processes or tasks, the operating system may struggle to allocate sufficient resources to all tasks, leading to starvation of some processes.
- Insufficient Resource Quotas: In some multi-user systems, resource quotas may be set for different users or processes. If a user or group exceeds their allocated quotas, their processes may be starved of the required resources.
Scheduling Algorithms to Prevent Starvation in OS
To prevent starvation in operating systems, various scheduling algorithms and techniques are employed to ensure fair resource allocation and give every process a chance to execute. Some of the commonly used scheduling algorithms to prevent starvation are:
- Round Robin Scheduling: Round Robin is a popular time-sharing scheduling algorithm. It allocates each process a fixed time slice or quantum of CPU time. Once a process’s time slice expires, it is moved to the end of the ready queue, allowing other processes to get a chance to execute. This way, every process gets a fair share of CPU time, reducing the risk of starvation.
- Priority-Based Scheduling with Aging: Priority-based scheduling assigns priorities to processes based on their importance or urgency. To avoid starvation of low-priority processes, priority aging is used. In priority aging, the priority of waiting processes gradually increases over time, ensuring that low-priority processes eventually get a chance to execute.
- Lottery Scheduling: Lottery scheduling assigns each process a certain number of lottery tickets. The CPU scheduler then randomly selects a ticket from the pool and allocates CPU time to the process holding that ticket. Processes with more tickets have a higher chance of getting CPU time, but every process has at least one ticket, preventing starvation.
- Fair Share Scheduling: Fair share scheduling ensures that each user or group gets a fair share of CPU time and other resources. It allocates resources based on predefined quotas, and when a process reaches its quota, it is temporarily paused, allowing other processes to run.
- Multilevel Queue Scheduling: Multilevel queue scheduling categorizes processes into multiple queues based on their priorities or characteristics. Each queue has its own scheduling algorithm. This approach ensures that every process gets a chance to execute, regardless of its priority, as it will be placed in an appropriate queue.
- Priority Inheritance: Priority inheritance is a technique used to prevent priority inversion and subsequent starvation. When a low-priority task holds a resource required by a high-priority task, priority inheritance temporarily elevates the priority of the low-priority task to the priority of the highest waiting task, ensuring prompt resource release.
Example of Starvation in OS
The P2 process in the provided example is given the highest priority, while P1 is given the lowest priority. There are n processes that are ready to be executed, as shown in the diagram. As a result, P2 will enter the CPU as the process with the greatest priority, while P1 will continue to wait for its turn because P1 is low on the priority list for all other processes. Starvation is the term used to describe the state in which the process is waiting.
In conclusion, understanding the concept of starvation in operating systems is crucial for system designers, developers, and administrators to ensure efficient resource management and fair process execution. Starvation occurs when certain processes or threads are deprived of essential resources due to the presence of higher-priority tasks or inefficient scheduling algorithms. As a result, starved processes may be unable to make progress and get stuck in indefinite waiting states.
To mitigate the risk of starvation, modern operating systems employ various scheduling algorithms and techniques. Round Robin, Priority-Based Scheduling with Aging, Lottery Scheduling, Fair Share Scheduling, Multilevel Queue Scheduling, and Priority Inheritance are some of the approaches used to prevent resource starvation and ensure equitable resource allocation.
FAQ on Starvation in OS:
Here are a few FAQs on Starvation in OS.
Q1. Why is preventing starvation important?
A1. Preventing starvation is essential for maintaining system stability, responsiveness, and optimal performance. It ensures that all processes get a fair share of resources, leading to a balanced and efficiently functioning operating system.
Q2. What causes starvation in operating systems?
A2. Starvation can be caused by factors like priority inversion, priority-based scheduling, resource mismanagement, deadlock, overload, and insufficient resource quotas.
Q3. How does starvation affect system performance?
A3. Starvation can impact system performance by delaying critical tasks of starved processes, reducing system responsiveness, and inefficiently utilizing available resources.
Q4. How can operating systems prevent starvation?
A4. Operating systems use various scheduling algorithms and techniques like priority aging, round-robin scheduling, fair share scheduling, and priority inheritance to prevent starvation and ensure fair resource allocation.