Concurrency and Multitasking in Operating Systems

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Questions and Answers

What happens when a thread blocks waiting for some file I/O?

It is terminated.
It is removed from the ready queue.
It is dispatched to run immediately.
It is moved to the end of the ready queue. (correct)

What is the purpose of the pthread_yield() function?

To exit the current thread.
To create a new thread.
To tell the scheduler to run another thread if available. (correct)
To wait for a thread to exit.

What happens when a newly created thread is added to the ready queue?

It is dispatched to run immediately.
It is added to the end of the ready queue. (correct)
It is removed from the ready queue.
It is added to the beginning of the ready queue.

What is the order of execution of threads in the ready queue?

Nondeterministic. (A) Signup and view all the answers

What is the purpose of the pthread_join() function?

To wait for a thread to exit and receive its return value. (D) Signup and view all the answers

What happens when a thread is context switched?

It is added to the end of the ready queue. (B) Signup and view all the answers

What is the purpose of the pthread_exit() function?

To destroy the current thread and return a pointer to its return value. (C) Signup and view all the answers

What is the effect of having multiple cores on thread scheduling?

It increases the number of threads that can run simultaneously. (C) Signup and view all the answers

What is the main difference between preemptive multitasking and parallelism?

Parallelism uses multiple processors, whereas multitasking uses a single processor. (A) Signup and view all the answers

What is the benefit of concurrency in multitasking OS?

It increases processor utilization. (B) Signup and view all the answers

What is the advantage of using threads over processes?

Threads take less system resources to create and manage. (B) Signup and view all the answers

Why do threads enable a single process to use multiple processors or cores?

Because threads enable parallelism. (D) Signup and view all the answers

What is an advantage of using threads for responsiveness?

One thread can be responsible for the user interface and others for loading a web page. (B) Signup and view all the answers

What is the benefit of using threads with different priorities?

Threads with higher priority get quicker access to the processor. (B) Signup and view all the answers

What does the kernel do when one process blocks?

The kernel runs another process. (B) Signup and view all the answers

What is the result of running A and B concurrently?

It takes less time for B to complete. (A) Signup and view all the answers

What is the purpose of a context switch in a program?

To switch from one thread running to another (A) Signup and view all the answers

What is preemption in the context of thread scheduling?

When the kernel involuntarily stops a thread (B) Signup and view all the answers

What is the primary purpose of a timer interrupt in a multi-threaded program?

To allow for different threads to have different sized quantums (A) Signup and view all the answers

What is a scheduling quantum in the context of thread scheduling?

The amount of time a thread executes on the processor core (C) Signup and view all the answers

What causes a context switch to occur in a multi-threaded program?

When a thread is waiting for a resource or I/O, or when a timer interrupt occurs (C) Signup and view all the answers

What is the purpose of a kernel thread in a multi-threaded program?

To handle device interrupts and context switches (D) Signup and view all the answers

What is the primary advantage of using multiple threads in a program?

Increased resource utilization and efficiency (C) Signup and view all the answers

What is the primary purpose of a system call in a multi-threaded program?

To request services from the kernel or operating system (C) Signup and view all the answers

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Study Notes

Concurrency and Multitasking

Preemptive multitasking (timesharing) allows multiple processes to run concurrently, rapidly switching between them to make progress.
Parallelism enables multiple processes to run simultaneously with hardware support (e.g., multiple processors or cores).
Multitasking OS can have multiple processes existing at the same time, with benefits including increased processor utilization and reduced latency.

Benefits of Timesharing

Increased processor utilization by overlapping computation time with I/O waiting time.
Reduced latency (time between launching a program and getting a response) compared to sequential execution.

Threads Abstraction

Threads are a lighter-weight abstraction than processes, requiring less system resources (processor time and memory) to create and manage.
Threads enable a single process to use multiple processors or cores in parallel, overlap I/O and computation, and prioritize tasks.

Thread Management

Context switching involves switching from one thread to another, which can happen due to thread yielding, blocking, or kernel preemption.
Newly created and unblocked threads are placed at the end of the ready queue, with nondeterministic running order.
POSIX thread API provides functions for creating threads (pthread_create), exiting threads (pthread_exit), joining threads (pthread_join), and yielding threads (pthread_yield).

Scheduling and Context Switching

Scheduling involves arranging threads to run concurrently, prioritizing tasks, and minimizing latency.
Context switching can occur due to thread yielding, blocking, or preemption by the kernel.
Preemption can occur due to timer interrupts, system calls, page faults, or device interrupts.