pthread_create
- C course
- Advanced
- Lesson 19/83
- 5 min
Learn to create threads with pthread_create.
pthread_create
pthread_create creates a new thread. It takes four parameters: thread ID, attributes, start function and the argument to pass to the function.
The function signature must be void *(*start)(void *); it takes void * and returns void *. For example, pthread_create(&tid, NULL, worker, &value) runs worker in a new thread. NULL attributes use defaults. The thread starts running as soon as it is created.
Thread lifecycle
When a thread is created it starts running and lives until its function returns. When the function returns, the thread ends.
To wait for its end you use pthread_join(tid, NULL). It waits until the thread returns and releases resources. Calling join for every created thread is a good habit; you will see the details in the next lesson. The thread shares memory with the parent thread.
Practice Create and join a thread
Write void *worker(void *arg) with int *value = (int *)arg; *value = 42;. Declare int value = 0;. Call pthread_create(&tid, NULL, worker, &value); and pthread_join(tid, NULL);. Print with printf("value=%d\n", value);.
Starter code
#include <stdio.h>
#include <pthread.h>
// Write worker function
// Create with pthread_create
// Join and print
int main(void) {
return 0;
}Sample solution
#include <stdio.h>
#include <pthread.h>
void *worker(void *arg) {
int *value = (int *)arg;
*value = 42;
return NULL;
}
int main(void) {
pthread_t tid;
int value = 0;
pthread_create(&tid, NULL, worker, &value);
pthread_join(tid, NULL);
printf("value=%d\n", value);
return 0;
}Expected output
value=42
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the third parameter of pthread_create?
- Attributes
- The thread ID
- The start function Correct answer
- The return value
Explanation: The third parameter is the start function.
2 Thread creation
pthread_create(&tid, NULL, ____, &value);pthread_create(&tid, NULL, worker, &value);Explanation: The worker function runs in the new thread.
3 Match pthread_create parts
| Term | Meaning |
|---|---|
pthread_create |
Starts thread |
pthread_join |
Waits for end |
NULL |
Default attributes |
void * |
Argument and return type |