Practice · Processes, Threads and Resource Management

Q1

Which resource is preemptable?

A An exclusive write lock in the middle of an update B A DVD burner writing a disc C A printer halfway through printing a document D The CPU

Q2

A message sent from one process to another is used up when it is received. It is a…

A preemptable resource B consumable resource C reusable resource D sharable resource

Q3

What is the difference between a program and a process?

A There is no difference. B A program is a passive file of instructions; a process is an active instance of a program with its own state and resources. C A program always has several processes. D A process is stored on disk; a program runs in memory.

Q4

Where are a function's local variables and return address stored?

A Stack B Data segment C Heap D Text segment

Q5

Which item is not normally stored in a process control block?

A The saved program counter and registers B The list of open files C The process state D The source code of the program

Q6

A running process requests to read a file from disk. Which state does it move to?

A Ready B Blocked (waiting) C Terminated D New

Q7

The disk read of a blocked process completes. What happens next?

A The process immediately moves to Running. B The process terminates. C The process moves to Ready and waits to be dispatched by the scheduler. D The process stays blocked forever.

Q8

Which transition is invalid in the five-state model?

A Running → Ready B Running → Terminated C Ready → Blocked D Blocked → Ready

Q9

A running process's time slice expires. Which transition occurs?

A Running → Ready (timeout / preemption) B Running → New C Running → Suspended-blocked D Running → Blocked

Q10

Memory is full, and the OS moves a blocked process's memory to disk. Which state does it enter?

A Suspended-ready B Running C Suspended-blocked D Terminated

Q11

The time slice is q = 1 ms and a context switch costs s = 0.1 ms. What fraction of CPU time is useful work?

A 90.91% B 50.00% C 99.01% D 10.00%

Q12

20 processes take turns with q = 10 ms and s = 0.1 ms. What is the maximum time a process may wait before its next turn?

A 100 ms B 191.9 ms C 202 ms D 10.1 ms

Q13

Why is a context switch considered overhead?

A The CPU saves and loads state (and caches become cold) without doing any useful work for the processes. B It only happens at boot time. C It runs user code faster. D It creates a new process.

Q14

What does fork() return in the child process?

A The parent's PID B 0 C The child's own PID D −1

Q15

How many times is "hi" printed?

fork();
fork();
fork();
printf("hi\n");

A 6 B 4 C 3 D 8

Q16

How many new processes (not counting the original) are created by for (i = 0; i < 4; i++) fork();?

A 16 B 15 C 4 D 8

Q17

What does execve do?

A Waits for a child to finish B Replaces the calling process's program with a new program, keeping the same PID C Creates a copy of the calling process D Sends a signal

Q18

ps shows many processes in state Z. What is the most likely cause?

A The processes are using too much CPU. B The disk is too slow. C A parent process creates children but never calls wait() to collect their exit status. D The processes are orphans adopted by PID 1.

Q19

Which is shared among the threads of one process?

A The heap and global variables B The program counter C The stack D The registers

Q20

A program uses many user-level threads mapped onto a single kernel thread (many-to-one). One thread makes a blocking disk read. What happens?

A The OS creates a new process. B The disk read becomes non-blocking automatically. C The whole process may block, because the kernel sees only one thread. D Only that thread blocks; the others continue on other cores.

Q21

Which threading model do Linux and Windows use for ordinary threads?

A Many-to-one B None; they do not support threads C Zero-to-many D One-to-one

Q22

Why do web and edge servers use a thread pool instead of creating one thread per request?

A Thread pools disable multitasking. B Threads cannot be created after startup. C Thread pools make each request use more memory. D Reusing a fixed number of threads avoids repeated creation cost and prevents thousands of threads from exhausting memory under load.

Q23

One thread in a process dereferences a null pointer and crashes. What happens to the other threads of the same process?

A The whole process — all its threads — is terminated. B They become zombies. C They continue normally. D They are moved to another process.

Q24

Where does an object created with new in Java (or malloc in C) live?

A In the text segment B In the process control block C In a CPU register D On the heap

Q25

Java 21 virtual threads let a server run a million concurrent tasks on a few kernel threads. Which threading model is this closest to?

A Single-threaded batch B One-to-one C Many-to-many (many lightweight threads multiplexed over fewer kernel threads) D One process per task

Q26

Which Linux mechanism limits the CPU and memory usable by a group of processes (the basis of container resource limits)?

A cgroups (control groups) B The file allocation table C The interrupt vector table D The boot loader

Q27 Short answer

Draw (in words or ASCII) the process state diagram with seven states (new, ready, running, blocked, terminated, suspended-ready, suspended-blocked) and name the event for each transition.

Q28 Short answer

A time-sharing server runs 12 interactive processes. The context-switch cost is 0.2 ms. Compute the CPU efficiency and the worst-case wait before a process runs again for q = 2 ms and q = 20 ms. Which q would you choose if users need a response within 100 ms?

Q29 Short answer

Explain what a zombie process and an orphan process are, how each arises, and how the OS deals with each.

Q30 Short answer

EdgeCampus runs a video-analytics service that handles 40 camera streams. Compare three designs: (a) one process per camera, (b) one process with one thread per camera, (c) one process with a thread pool of 8 workers. Discuss isolation, memory, CPU use on an 8-core server and behaviour under failures.