Lecture 06 - Threads

Question 1

What does each thread get its own copy of?

Answer 1

Automatic variables (function variables)

Question 2

What data do threads share?

Answer 2

• Open file handles and sockets
• Global variables
• Memory allocated with malloc

Question 3

Give four reasons threads are useful

Answer 3

• Increased responsiveness
• Ease of communication between threads
• Scalability
• Handling asynchronous events

Question 4

How do threads increase the responsiveness of a program?

Answer 4

There can be separate threads for IO while others do computation.

Question 5

What library implements POSIX threads?

Answer 5

pthreads

Question 6

What is the function used to create a new thread in C?

Answer 6

pthread_create()

Question 7

What is the function prototype of pthread_create?

Answer 7

int pthread_create(
        pthread_t *restrict thread,
        const pthread_attr_t *restrict attr,
        void *(*start_routine)(void*),
        void *restrict arg);

Question 8

What are two ways for a thread to exit?

Answer 8

• It returns from its start routine

- It calls pthread_exit

Question 9

What is the function prototype for pthread_exit?

Answer 9

void pthread_exit(void *value_ptr);

Question 10

What happens to threads when a process terminates?

Answer 10

They also terminate.

Question 11

What function is used to get the current thread’s ID?

Answer 11

pthread_self

Question 12

What is the function prototype for pthread_self?

Answer 12

pthread_t pthread_self(void);

Question 13

What makes a function thread-safe?

Answer 13

When the correct result is produced in the face of simultaneous execution.

Question 14

What gcc parameter is used to link the pthread library?

Answer 14

-pthread

Question 15

What function is used to wait for a thread to terminate?

Answer 15

pthread_join

Question 16

What does the pthread_join function do?

Answer 16

Waits for a thread to terminate and receives its return value.

Question 17

What is the function prototype for pthread_join?

Answer 17

int pthread_join(pthread_t thread, void **value_ptr);

Question 18

What function is used to request termination of another thread?

Answer 18

pthread_cancel

Question 19

What is the function prototype of pthread_cancel?

Answer 19

int pthread_cancel(pthread_t thread);

Question 20

What does the pthread_cancel function do?

Answer 20

Requests the termination of another thread.