Starvation - TarisMajor/5143-OpSystems GitHub Wiki

starvation-in-os-operating-system-1

Starvation in the context of operating systems and concurrent programming refers to a situation where a process or thread is perpetually denied the necessary resources to proceed with its execution. This typically occurs because other processes or threads are continuously being allocated the resources that the starving process needs. Starvation can significantly affect system performance and fairness, making it a critical issue to address in system design.

Key Characteristics of Starvation

  1. Indefinite Blocking: The affected process or thread remains in a waiting state indefinitely, unable to progress because it cannot acquire the required resources.
  2. Resource Allocation: Starvation is often a result of resource allocation policies that favor certain processes or threads over others.
  3. Priority-Based Scheduling: Starvation frequently occurs in priority-based scheduling systems where higher-priority processes consistently preempt lower-priority ones.

Causes of Starvation

  1. Priority Inversion: Lower-priority processes may starve if higher-priority processes continually receive the resources they need.
  2. Inadequate Resource Management: Poorly designed resource allocation mechanisms can lead to some processes never getting access to the required resources.
  3. Frequent Preemption: In systems with frequent preemptions, certain processes may repeatedly lose out on resources to other processes.
  4. Static Priorities: In systems with static priorities, low-priority processes may be overshadowed by higher-priority processes that continually enter the system.

Solutions for Preventing Starvation

  1. Aging: A technique where the priority of a waiting process gradually increases over time, ensuring that it eventually gets access to the required resources. This prevents indefinite blocking.
  2. Fairness Algorithms: Implementing fairness in scheduling algorithms, such as Round Robin or fair share scheduling, ensures that all processes get a fair share of CPU time and resources.
  3. Dynamic Priority Adjustment: Dynamically adjusting the priorities of processes based on their waiting time and resource requirements can help prevent starvation.
  4. Resource Allocation Policies: Designing and implementing resource allocation policies that consider fairness and prevent perpetual denial of resources to any process.

Use Cases for Starvation Prevention

  1. Operating Systems: Ensuring fairness and preventing starvation in operating systems is critical for maintaining system stability and performance.
  2. Multithreaded Applications: In multithreaded applications, preventing starvation ensures that all threads can make progress and contribute to the application's functionality.
  3. Real-Time Systems: In real-time systems, preventing starvation is essential to meet deadlines and ensure timely execution of critical tasks.

Example of Starvation

Consider a priority scheduling system with three processes:

  1. Process P1: High-priority process.
  2. Process P2: Medium-priority process.
  3. Process P3: Low-priority process.

If P1 and P2 continually require CPU time, P3 may never get scheduled, leading to starvation.

Solution with Aging:

  • P3's priority can be gradually increased the longer it waits. Eventually, its priority will surpass P1 and P2, allowing it to be scheduled and preventing starvation.

Sources for Further Reading