370 #5 - Concurrency, Interprocess Communication And Deadlock

A binary semaphore is a synchronization primitive that can have only two states - 0 or 1. When initialized to 1, it works like a lock where only one process can access the shared resource at a time. The incorrect answers do not accurately describe the purpose of a binary semaphore.

The correct answer explains how negative semaphore values provide information about the status of threads waiting for resources in the queue, resources being free, and the overall state of the semaphore.

The Readers/Writers Problem is a classic synchronization problem where multiple threads need to access shared data. The correct answer outlines the main rules that need to be followed to ensure data integrity. The incorrect answers provided misinterpret the basic principles of the problem and do not align with the requirements for readers and writers accessing the shared data.

The Readers/Writers problem deals with synchronization issues in concurrent programming. In this problem, multiple threads or processes compete for access to a shared resource, such as a database. The different solutions include Writer preferred (giving priority to writers over readers), Reader preferred (giving priority to readers over writers), and Neither preferred (no preference between readers and writers).

In the Writer Preferred solution for Readers/Writers problem, waiting writers are given priority over waiting readers. This strategy ensures that writers do not face indefinite postponement, as they are allowed access to the resource once all remaining readers have finished. Allowing readers to go before waiting writers or giving access to both simultaneously can cause various issues like data inconsistency or deadlock situations, making them incorrect options.

The correct answer follows the reader preferred approach in readers/writers solutions where waiting readers are given priority over waiting writers. This approach can potentially lead to an indefinite postponement of writers as readers continue to access the resource.

In Readers/Writers Solutions, fairness is key in order to balance the needs of readers and writers without showing preference to either side. By focusing on a single queue and allowing parallel readers when possible, the system can maintain efficiency and equitable access to data.

Concurrency can lead to issues such as race conditions, deadlocks, and resource contention due to multiple threads accessing shared resources simultaneously.

A Race Condition in programming occurs when the order of execution of threads can lead to unexpected and unpredictable results, as programmers have no control over the exact timing of thread execution.

In a critical section of code, it is essential to allow only one thread to be active at a time to avoid race conditions and ensure data integrity.

Mutual Exclusion involves restricting access to a critical section to only one thread at a time to prevent interference and maintain data integrity.

Starvation due to mutual exclusion can occur in multi-threaded environments when certain threads are unable to access a shared resource indefinitely, leading to issues such as deadlock and indefinite postponement. Other causes of starvation can include resource exhaustion, livelock, and thread starvation.

The correct answer highlights the issues of busy waiting, lack of control over lock release prioritization, and potential race conditions. The first incorrect answer misinterprets the presence of spinning in the scenario. The second incorrect answer inaccurately states that threads do not have access to the lock variable. The third incorrect answer incorrectly assumes that once a thread sets the lock to true, it cannot be changed by another thread, which is not the case in the described scenario.

Spin-Lock // Busy Wait involves continuously checking for a condition to be satisfied instead of waiting or sleeping. This can result in the wastage of CPU cycles without any productive work being done, thereby reducing efficiency and potentially causing delays in other processes.

Peterson's Solution version 1 works specifically on shared memory multiprocessors with certain limitations and requirements.

Peterson's Solution is a synchronization algorithm used for achieving mutual exclusion in critical sections. While it is effective in some scenarios, it has limitations such as only working with two threads and involving busy waiting, which consumes CPU resources unnecessarily.

The correct answer involves raising the interrupt priority level to prevent any other process from running while the lock is being tested. Lowering the interrupt priority level (option A) would not help in preventing the gap between checking and setting the lock. Keeping the priority level unchanged (option B) would not address the issue. Implementing a time-based lock-checking mechanism (option C) may introduce new complexities and overhead. Using a different synchronization mechanism (option D) could be a valid approach but does not directly address the specific issue with Peterson's solution.

Interrupt Priority Levels can pose challenges in managing processes and system resources, especially in scenarios where not all processes need to be stopped at the current interrupt priority level. This can lead to inefficiencies on multiprocessors and delays in communication among processors.

Test and Set is a mechanism used to ensure that certain operations on shared variables are performed atomically, without interference from other threads. It is necessary for synchronization in multi-threaded environments to prevent race conditions. The correct answer explains the key characteristics of Test and Set, including its indivisibility and interruptability. The incorrect answers provide misleading information about how Test and Set operates.

The correct answer highlights that in this scenario, one thread can be made to wait while another thread gets access to the resource multiple times, potentially leading to unfairness in resource allocation.

The question revolves around the impact of priority levels in spin locks. High priority threads getting prior access can make the mechanism more effective but increases the risk of indefinite postponement due to lower priority tasks being constantly preempted.

Priority Inversion is a phenomenon in scheduling where a higher priority task is delayed by a lower priority task due to resource contention. It typically involves three threads with different priorities and the situation described in the correct answer illustrates how priority inversion can occur.

Priority Inheritance is a mechanism used to solve the problem of priority inversion in scheduling algorithms. It ensures that a higher priority task inherits the priority of a lower priority task holding shared resources.

Priority Inheritance is a technique used in real-time systems to prevent priority inversion problem. It ensures that a high priority process waiting for a resource held by a lower priority process will be temporarily given the priority of the lower priority process to prevent indefinite blocking.

Putting a thread that must wait in a queue helps in solving fairness and wasting processor cycles by ensuring that threads do not continuously compete for lock resources, leading to a more efficient and equitable system operation.

Placing a thread that must wait on a queue and stopping it from running can potentially free up pages for other processes and provide visibility into the number of threads waiting for the resource, thus aiding in resource management. Incorrect answers include allowing the thread to consume additional resources, improving system performance without proper context, and increasing the risk of deadlock.

The correct answer highlights the issue of nothing waiting on the queue while the lock is held, which can lead to threads going to sleep unnecessarily. The solution provided involves using a spin lock to prevent this scenario.