Multithreading in C interview questions

Q1. What exactly is a thread?

Ans: A thread is a brief sequence of instructions intended to be planned and carried out by the CPU apart from the parent process.

Q2. Can we create applications with several threads in C?

Ans: No, in contrast to Java, the C language standard does not support multithreading. The POSIX standard for threads is called POSIX Threads (or Pthreads). Only with the gcc compiler, pthread implementation is provided.

A C program to show multiple threads with global and static variables.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
 
// Make a global variable so we can modify it in threads.
int m = 0;
 
// The procedure that each thread will run
void *myThreadKam(void *vargp)
{
    // Specify the value of the thread's argument.
    int *myid = (int *)vargp;
 
    // To track changes in a static variable, let's construct one
    static int g = 0;
 
    // Change static and global variables
    ++g; ++m;
 
    // Print the argument, static and the global variables
    printf("Thread ID: %d, Static: %d, Global: %d\n", *myid, ++g, ++m);
}
 
int main()
{
    int i;
    pthread_t tid;
 
    // Let us create three threads
    for (i = 0; i < 3; i++)
        pthread_create(&tid, NULL, myThreadKam, (void *)&tid);
 
    pthread_exit(NULL);
    return 0;
}

Output

Q3. Describe multithreading.

Ans: Executing multiple threads at once is known as multithreading.

Q4. Why use multiple threads?

Ans: A common method for enhancing applications through parallelism is to use threads. For instance, many tabs in a browser could represent various threads. Multiple threads are used by MS Word; one thread is used to format the text, another to handle inputs, etc.

Q5. What are the thread's associated states?

Ans: State: ready, running, waiting, dead.

Q6. Explain about the Thread Life Cycle

Ans: A thread's life cycle is comparable to the processes that make up an operating system. Throughout its lifetime, the thread has the ability to change states at any time. But that depends on the procedure carried out on it.

Q7. What states are there in a thread?

Ans: New: A newly created thread is in its initial state. The thread enters the ready state after using some method regarding this. The thread scheduler then moves it to the runnable state.

Runnable: A thread that is prepared to run.

Running: A thread in running state is one that is actively working.

Blocked: This state has a blocked thread that is expecting a monitor lock. This can also happen when a thread changes states while performing an I/O operation.

Waiting: It is a thread that is holding up activity while another thread does the required action.

Timed_waiting: It's a thread that is awaiting action from another thread.

Terminated: This state describes a terminated thread.

Q9. What key distinctions exist between Thread and Process?

Ans: Process is a subset of the thread. There may be several threads in the process. The memory space that the process uses can vary, but all threads share the same memory area.

Q10. What is deadlock?

Ans: Deadlocks occur when two threads are waiting for object locks that one has already obtained while the other is waiting for a lock that the first thread already has.

Q11. What is LiveLock?

Ans: Due to the lack of necessary resources and the absence of unblocked threads, livelock occurs when all threads are blocked and unable to execute.

Q12. What does multi-busy threading's spin term mean?

Ans: Concurrent programmers use the busy spin technique to force a thread to wait until a specific condition is met. This differs significantly from conventional techniques like wait() and sleep(), which all involve giving up CPU control. Instead of turning off the CPU, this technique just executes the empty loop.

Q13. What does multi-threading context switch entail?

Ans: The process of saving and recovering CPU state is what it entails. This makes it easier to pick up thread execution from the same place at a later time. It is one of the key components of an operating system that supports multiple tasks at once and a multi-threaded environment.

Q14. Why does Thread behaviour fluctuate?

Ans: Because the execution of threads is dependent on the thread scheduler, we might conclude that thread behaviour is unpredictable. One should remember that each thread scheduler has a unique implementation on various operating systems, such as Windows, Unix, etc.

Q15. What does the term "Thread Priority" mean?

Ans: Each thread is given a priority. But in terms of execution, a greater priority also takes precedence. However, it also depends on how the OS implements the Thread Scheduler. Although the priority of the thread can be changed, there is no guarantee that a higher priority thread will be performed first.