chapter 27 - interlude: thread API

Question 1

How do you create a new thread in POSIX?

Answer 1

Use pthread_create

Question 2

What does the fourth argument of pthread_create() do?

Answer 2

It passes a void* argument to the new thread’s function - allowing any type of data to be passed

Question 3

How do you wait for a thread to finish in POSIX?

Answer 3

Use pthread_join(pthread_t thread, void **retval);

Question 4

Why should you not return a pointer to a stack variable from a thread?

Answer 4

Because the stack is destroyed when the thread ends — leading to undefined behavior

Question 5

What should you pass to pthread_join() if you don’t care about the return value?

Answer 5

NULL

Question 6

What functions are used to protect critical sections in pthreads?

Answer 6

pthread_mutex_lock()

pthread_mutex_unlock()

Question 7

What is pthread_mutex_trylock() used for?

Answer 7

It tries to acquire the lock without blocking — returns immediately if the lock is bus

Question 8

What is pthread_mutex_timedlock() used for?

Answer 8

Waits for a lock up to a specified timeout

Question 9

What is a condition variable used for in pthreads?

Answer 9

To allow threads to wait for a condition to become true — enables signaling between threads

Question 10

What do you need to include and link to use pthreads in C?

Answer 10

Include <pthread.h></pthread.h>

Compile with the -pthread flag