pthread_self() returns the same value across after fork()

output

kostja@atlas ~ % gcc -pthread foo.c; ./a.out
thread id: 140508398954304
thread id: 140508398954304
thread id: 140508398954304

pthread_self

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int main()
{
	printf("thread id: %llu\n", (unsigned long long) pthread_self());
	fork();
	printf("thread id: %llu\n", (unsigned long long) pthread_self());
}