Linux kernel quiz: Why is this program so slow and takes around 50ms to run?
What line do you have to add to make it run in 3ms instead without interfering with what this program does?

user@debian12:/test$ cat > slow.c
#include 
#include 
#include 
#include 

static void open_sockets(void) {
 for (int i=0; i<256; i++) {
 int sock = socket(AF_INET, SOCK_STREAM, 0);
 if (sock == -1)
 err(1, "socket");
 }
}

static void *thread_fn(void *dummy) {
 open_sockets();
 return NULL;
}

int main(void) {
 pthread_t thread;
 if (pthread_create(&thread, NULL, thread_fn, NULL))
 errx(1, "pthread_create");
 open_sockets();
 if (pthread_join(thread, NULL))
 errx(1, "pthread_join");
 return 0;
}
user@debian12:/test$ gcc -O2 -o slow slow.c -Wall
user@debian12:/test$ time ./slow

real 0m0.041s
user 0m0.003s
sys 0m0.000s
user@debian12:/test$ time ./slow

real 0m0.053s
user 0m0.003s
sys 0m0.000s
user@debian12:/test$