Non Preemptive Priority

Operating systems use the scheduling algorithm non-preemptive priority scheduling to choose the sequence in which processes are carried out. Each process is given a priority value based on specific criteria, and the procedure with the highest priority is carried out first.

In this article, we will be discussing Non-Preemptive Priority, the much-needed Process of Prioritization with some examples, and some strategies to prevent starvation in terms of Non-Preemptive Priority.

What is Non-Preemptive Priority?

A process in non-preemptive priority scheduling keeps running until it is finished or voluntarily enters a waiting state. A higher-priority process is not halted by the scheduler to make room for a lower-priority process. This means that a lower-priority process could have to wait until the higher-priority process that is now running completes.

The quantity of CPU time needed, the significance of the operation, or the deadline related to the process can all affect the priority value assigned to processes. Depending on the specific implementation or operating system, the precise mechanism of assigning priorities may change.

Non-preemptive priority scheduling has the disadvantage of perhaps causing a condition known as "starvation." Because there are always higher-priority processes running in the system, starvation happens when a low-priority process is never given the chance to run. Some implementations may have aging methods, which gradually raise a process' priority as it waits, preventing starvation by making sure that all processes eventually have a chance to run.

What is Process Prioritization and what are some of its elements?

Process prioritization is the process of giving processes in an operating system or scheduling algorithm priority values. The order in which a process is executed in relation to other processes is determined by the priority given to it.

The following are some critical elements of process prioritization−

Criteria for Priority Assignment − Different criteria might be taken into account when determining the priorities of processes. Some typical standards include−

• CPU Burst Time − Since they can finish their execution more rapidly, processes with shorter CPU burst periods could be given higher priority.

Example − To ensure fast playing and real-time reaction, real-time multimedia programs such as video editing software prioritize operations involved in rendering or encoding.

• Deadline Requirements − Processes with stringent deadline constraints could receive greater priority treatment in order to finish on time.

  Example − High-priority activities in air traffic management, like collision detection and resolution, have strict time constraints to guarantee the safety of aircraft.

• Importance − Due to their nature or criticality, some processes may be viewed as being more significant than others. Higher priorities may be given to certain procedures.

  Example − In order to respond quickly to life-threatening circumstances, emergency service processing systems like 911 call centers and ambulance dispatch systems are given top priority.

• I/O Intensive vs. CPU Intensive − Processes that heavily rely on I/O operations may be prioritized differently than those that are CPU-bound, depending on the system's characteristics.

  Example − CPU-intensive operations are given priority in complex simulations involving substantial computational calculations in order to speed up the production of results.

Priority Levels or Ranges − Priorities are frequently expressed as numbers or priority levels. Depending on the specific operating system or scheduling mechanism, the range of priority levels can change. A system might, for instance, utilize a value range from 0 to 99, where a greater number denotes a higher priority.

Priorities can be static or dynamic, depending on the situation.

• Static Priority − During their execution, processes are given a fixed priority that never changes.

• Dynamic Priority − Based on certain circumstances or occurrences, priorities may vary while a program is running. For instance, if a process has used a lot of CPU time, its priority may drop in a feedback-based scheduling mechanism.

Priority Inversion − Priority inversion is the phenomenon that happens when a resource needed by a high-priority process is held by a low-priority activity. The high-priority process's execution may be delayed as a result. Priority inversion is prevented or mitigated by using methods like priority inheritance or priority ceiling protocols.

Algorithms for Priority Scheduling − A number of scheduling algorithms employ process priorities to decide which tasks should be completed first. Preemptive priority scheduling, where a higher-priority process can preempt the execution of a lower-priority process, and non-preemptive priority scheduling, where the highest-priority process runs to completion before the next process is picked, are two examples of these algorithms.

Interplay with Other Scheduling Policies − Process prioritization can interact with other scheduling procedures such as round-robin or first-come, first-served (FCFS), among others. For instance, in a multi-level feedback queue scheduling method, processes may initially be given priorities based on their traits and then have those priorities dynamically changed based on their behavior.

How to Prevent Starvation in Terms of non-preemptive Priority Scheduling?

In the context of non-preemptive priority scheduling, starvation prevention strategies are crucial because they make sure that lower-priority operations are not continuously delayed and provide them a fair chance to be executed alongside higher-priority processes.

In the context of non-preemptive priority scheduling, strategies to prevent starvation include the following −

Aging − Gradually increasing the priority of waiting processes over time ensures that lower-priority processes eventually get a chance to execute alongside higher-priority processes.

Priority Boosting − Regularly raising the priority of processes that have been waiting for a long time provides them an opportunity to be executed, even if they have lower priorities.

Fair Share Scheduling − Distributing system resources proportionally among processes prevents any single process from monopolizing all resources. This ensures fairness and equal opportunities for all processes.

Priority Inheritance Protocols − When a lower-priority process holds a resource required by a higher-priority process, priority inheritance protocols temporarily raise the priority of the lower-priority process. This prevents resource deadlock and allows higher-priority processes to continue execution.

By implementing these preventive measures, non-preemptive priority scheduling can maintain fairness, avoid unnecessary delays, and provide every process with a chance to complete. Applying these techniques in operating systems can enhance system responsiveness and overall performance.

Conclusion

Operating systems use the scheduling algorithm non-preemptive priority scheduling to choose the sequence in which processes are carried out. Based on parameters like CPU burst time, deadline demands, importance, or other reasons, it provides priority levels to processes. A process begins running when it is given the greatest priority and continues until it is finished or voluntarily suspended.

Processes can be prioritized according to their importance or urgency using non-preemptive priority scheduling, which is quick and effective. With no interruptions, it makes sure that higher-priority processes run before lower-priority ones. However, if higher-priority processes keep arriving, low-priority processes may have to wait indefinitely, creating the problem of famine.