For example, a thread T1 running at priority 4 gets preempted by a higher-priority thread T2 with a priority of 8 after acquiring a lock. Subsequently, a thread T3 with a priority of 12 arrives, preempts T2, and gets blocked trying to acquire the lock held by T1.
Example. Suppose that both H and L require some shared resource. If L acquires this shared resource (entering a critical section), and H subsequently requires it, H will block until L releases it (leaving its critical section).
The Priority Ceiling protocol assigns priority ceilings to resources and prevents lower-priority tasks from blocking higher-priority ones, while Priority Inheritance allows tasks to temporarily inherit higher priorities. The former can prevent deadlocks, while the latter only mitigates their impact.
In the priority inheritance protocol, the mutex holder inherits the priority of the highest-priority blocked thread. When a thread tries to lock a mutex using this protocol and is blocked, the mutex owner temporarily receives the blocked thread's priority, if that priority is higher than the owner's.
In one line, Priority Inversion is a problem while Priority Inheritance is a solution. Priority Inversion means that the priority of tasks gets inverted and Priority Inheritance means that the priority of tasks gets inherited. Both of these phenomena happen in priority scheduling.
If a thread that had already locked a mutex, tries to lock the mutex again, it will enter into the waiting list of that mutex, which results in a deadlock. It is because no other thread can unlock the mutex.
Because priority inversion results in the execution of a lower-priority task blocking the high-priority task, it can lead to reduced system responsiveness or even the violation of response time guarantees. A similar problem called deadline interchange can occur within earliest deadline first scheduling (EDF).
Multilevel Inheritance - In this type of inheritance, a subclass derives properties from another subclass which in turn derives properties from another sub class or the super class. Hierarchical Inheritance - In this type of inheritance, multiple sub classes derive properties from a single super class.
A heap is a concrete implementation of the priority queue using an array (it can conceptually be represented as a particular kind of binary tree) to hold elements and specific algorithms to enforce invariants.
Another way to prevent priority inversion is to ensure that all tasks that access a common resource have the same priority. Although one task might still wait while another task uses the resource, no priority inversion will occur because both tasks have the same priority.
It dynamically assigns priorities to tasks, where the priority of a waiting task is raised to the priority of the task it is waiting for. This protocol helps in avoiding ineffective priority queues and enables scheduling decisions to be made at the time of action.
In this example, Animal is the superclass, Dog is the subclass of Animal, and Labrador is the subclass of Dog. The Labrador class inherits the eat() method from the Animal class and the bark() method from the Dog class.
Priority ceiling was created to avoid priority inversion. A well implemented algorithm would always give each process the highest priority that is associated with each of the resources held by that process (in this case semaphores).
A chord (triad, seventh chord, or any other chord) with the third scale degree in the bass and the root somewhere above is said to be in first inversion. For example, a C major chord instead of being played C-E-G, would be played E-G-C (3-5-1), or E-C-G (3-1-5).
In general, an operating system (OS) is responsible for managing the hardware resources of a computer and hosting applications that run on the computer. An RTOS performs these tasks, but is also specially designed to run applications with very precise timing and a high degree of reliability.
An example of hierarchical inheritance is when a 'Car' class is derived from both a 'Vehicle' class and a 'Gasoline' class. The 'Car' class would then be able to inherit both the properties of the 'Vehicle' class (such as its color and speed) and the properties of the 'Gasoline' class (such as its fuel efficiency).
In Java, the Diamond Problem is a common issue that arises with multiple inheritance. When a class inherits from multiple parent classes that have the same method or field, the compiler gets confused on which one to choose. This can lead to unexpected behavior and errors in the program.
The key difference between Multiple and Multilevel Inheritance is that Multiple Inheritance is when a class inherits from many base classes while Multilevel Inheritance is when a class inherits from a derived class making that derived class a base class for a new class.
The problem arises if Thread 3 should become ready while Thread 2 has the resource locked. Thread 3 preempts Thread 2. This situation is called priority inversion, because a lower priority thread (Thread 3) is effectively preventing a higher priority thread (Thread 1) from executing.
Starvation in OS is a problem that occurs when low-priority processes are indefinitely blocked from executing due to high-priority processes. This typically happens in a scheduling system, where certain low-priority processes are repeatedly overlooked in favor of high-priority ones.
To keep it simple: Deadlock occurs when no process is able to proceed further due to circular waiting amongst the processes. Livelock occurs when there is multiple processes are live(ready/running) but blocked together due to Priority Inversion Problem.
Semaphores allow multiple threads or processes to access a shared resource with limited capacity, while mutexes only allow one thread or process to access a shared resource at a time. Both mechanisms help prevent race conditions and ensure that shared resources are accessed in a controlled and synchronized manner.
One of the simplest and most effective ways to avoid deadlocks is to follow a consistent order of locking resources when executing transactions. For example, if you have two transactions that need to access tables A and B, make sure they both lock A before B, or vice versa.
Yes, you lock the mutex or critical section but forget to unlock it (say in a certain exit code path). The next thread that tries to access this code is a deadlock.