Priority Inheritance Protocol (PIP) in Synchronization

On a single CPU, many processes may operate simultaneously under an operating system that supports multitasking. Synchronization strategies are used to organize access to shared resources. Priority inversion, on the other hand, happens when a high-priority activity is obstructed by a lower-priority process that is holding a shared resource, and it can be caused via synchronization. The Priority Inheritance Protocol (PIP), a synchronization method used to resolve the priority inversion problem, will be explained in this article.

The priority inversion problem is solved using the Priority Inheritance Protocol (PIP), a synchronization method. PIP gives the task in possession of a shared resource the greatest priority among other jobs awaiting that resource. The shared resource will be accessible by the high-priority activity without being obstructed by a lower-priority task thanks to this priority inheritance. PIP is important since it stops priority inversion without affecting the task hierarchy's priority order. To put it another way, a task's priority does not change until it uses a shared resource. Real-time operating systems like VxWorks, QNX, and eCos frequently employ PIP.

Methods to Overcome Priority Inversion Problem

Prior to PIP, binary semaphores and priority ceiling were the two methods utilized to overcome the priority inversion problem. Priority ceiling elevates a task's priority to the priority ceiling whenever it uses a shared resource and gives it a set priority. On the other hand, binary semaphores only permit one process at a time to access a shared resource. These methods do have certain drawbacks, though.

Priority ceiling can result in the "ceiling priority inversion" phenomenon, in which a lower-priority job that is holding a shared resource with a higher-priority ceiling blocks a higher-priority task. When two or more jobs are waiting for a resource that is being held by another process, binary semaphores might result in a condition known as "deadlock." PIP was created as a result to get around these restrictions.

Other Techniques for Solving Priority Inversion Problem

Several methods are employed in addition to PIP to address the priority inversion issue. One of these is the "priority ceiling with inheritance" strategy, which gives the task in possession of the resource the job with the greatest priority of all tasks waiting for a shared resource. This method likewise gives a shared resource a priority ceiling, but the priority ceiling can be increased to match the priority of the task with the greatest priority waiting for the resource.

The "priority inheritance ceiling" technique, a PIP version, is another method. It elevates the priority of a task that is holding a resource to the priority ceiling and gives a priority ceiling to a shared resource. In contrast to PIP, it also increases the priority of any job awaiting a resource.

Advantages of PIP Over Other Methods

PIP provides a number of benefits over other methods for solving the priority inversion problem. One benefit is that it avoids priority inversion without interfering with the task hierarchy's priority order. PIP makes sure that a task's priority doesn't change until it makes use of a shared resource. With the help of this function, higher-priority actions are protected from being blocked by lower-priority ones.

PIP also has the benefit of being simple to deploy and requiring little overhead. Priority inheritance is successfully achieved with PIP by just adding a small number of extra instructions to the operating system scheduler. PIP is also simple to deploy on a variety of hardware platforms because it doesn't require any hardware changes or specialist hardware support.

PIP does not significantly impair performance and is also effective. PIP makes sure that high-priority processes may use shared resources freely, without being hindered by lower-priority tasks, and without adding much overhead or delay. The system can operate effectively and fulfill its real-time needs thanks to its efficiency.

PIP Algorithm

Here is how the PIP algorithm operates −

• The priority of the lower-priority job is momentarily elevated to that of the high-priority task if a high-priority activity tries to access a shared resource owned by a lower-priority process.

• The shared resource is being held by the lower-priority job, but its priority is still equal to that of the high-priority activity. The shared resource may be used by the high-priority activity without being obstructed by the lower-priority task thanks to this priority inheritance.

• The higher-priority activity's priority is returned to it when the lower-priority task releases the shared resource.

Use Cases of PIP in Synchronization Operating Systems

To prevent lower-priority operations from obstructing higher-priority tasks from accessing shared resources, synchronization operating systems employ PIP. In real-time systems, when missed deadlines or delays might have major repercussions, this capability is very helpful.

In embedded systems, where real-time limitations are crucial, PIP is frequently used. PIP, for instance, may make sure that essential actions, like monitoring a patient's vital signs or giving medicine, are not impeded or delayed by less important ones in medical equipment.

Real-World Examples of PIP Implementation

PIP has been applied in several real-world scenarios, such as −

• Aerospace and Defense − PIP is used in avionics systems to guarantee that crucial processes, like flight control, aren't slowed down or prevented by less important ones.

• Industrial Automation − PIP is used in industrial automation systems to make sure that crucial operations, like managing a robotic arm or keeping track of a production process, are not impeded or delayed by less important ones.

• Medical Devices − PIP is used in medical devices to make sure that crucial actions, like keeping track of a patient's vital signs or giving medicine, are not slowed down or prevented by less important ones.

Comparison of PIP With Other Synchronization Techniques

PIP is superior to other synchronization methods for solving the priority inversion problem in a number of ways. PIP prevents ceiling priority inversion by ensuring that a task's priority stays the same up until it uses a shared resource, as opposed to a priority ceiling. PIP enhances system performance by enabling numerous jobs to use a shared resource concurrently as opposed to binary semaphores.

PIP has a few drawbacks in comparison to other synchronization methods. PIP does not raise the priority ceiling to the priority of the highest-priority task awaiting the resource, in contrast to the priority ceiling with inheritance. PIP does not increase the priority of any job awaiting a resource compared to the priority inheritance ceiling.

Analysis of PIP

PIP is a synchronization strategy that is effective and efficient for resolving the priority inversion issue in real-time systems. PIP makes ensuring that high-priority tasks are able to utilise shared resources without being hindered by lower-priority activities, maintaining the task hierarchy's priority.

PIP is appropriate for a variety of hardware platforms since it is simple to implement and entails little overhead. Aerospace and defence, industrial automation, and medical equipment are just a few of the real-world uses for PIP.

PIP has a few drawbacks in comparison to other synchronization methods. PIP does not raise the priority ceiling to the priority of the highest-priority task awaiting the resource, in contrast to the priority ceiling with inheritance. PIP does not increase the priority of any job awaiting a resource compared to the priority inheritance ceiling.

PIP is a generally useful and successful approach to the priority inversion issue. Although it has significant disadvantages in comparison to other synchronization methods, real-time systems frequently choose it because of its simplicity, effectiveness, and convenience of implementation.

Conclusion

In synchronization operating systems, priority inversion is a frequent issue that can cause delays and missed deadlines. PIP is a synchronization method that real-time systems utilize to address the priority inversion issue. PIP makes ensuring that high-priority tasks are able to utilize shared resources without being hindered by lower-priority activities, maintaining the task hierarchy's priority.

PIP is appropriate for a variety of hardware platforms since it is simple to implement and entails little overhead. Aerospace and defense, industrial automation, and medical equipment are just a few of the real-world uses for PIP. PIP is a common option for real-time systems despite having certain drawbacks in comparison to other synchronization strategies due to its simplicity, effectiveness, and ease of implementation.