Question

I’ve read about synchronized thread in Posix threads tutorial. They say that function pthread_join is used for waiting thread until it stops. But why doesn’t this idea work in that case?

Here is my code:

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

int a[5];

void* thread(void *params)
{
    cout << "Hello, thread!" << endl;

    cout << "How are you, thread? " << endl;

    cout << "I'm glad to see you, thread! " << endl;
}

void* thread2(void *params)
{
    cout << "Hello, second thread!" << endl;

    cout << "How are you, second thread? " << endl;

    cout << "I'm glad to see you, second thread! " << endl;

//    for (;;);

}

int main()
{
    pthread_t pt1, pt2;

    int iret = pthread_create(&pt1, NULL, thread, NULL);
    int iret2 = pthread_create(&pt2, NULL, thread2, NULL);

    cout << "Hello, world!" << endl;

    pthread_join(pt1, NULL);
    cout << "Hello, middle!" << endl;

    pthread_join(pt2, NULL);

    cout << "The END" << endl;
    return 0;
}

Answer 1

Threads are executed asynchronously, as someone already mentioned in answer to question you linked. Thread execution starts right after you create() it. So, at this point:

int iret = pthread_create(&pt1, NULL, thread, NULL);

thread() is already executing in another thread, possibly on another core (but it doesn’t really matter). If you add a for (;;); in your main() right after that, you will still see thread message being printed to console.

You also misunderstood what join() does. It waits for thread termination; as your threads don’t do any real work, they will (most probably) reach their ends and terminate way before you call join() on them. Once again: join() doesn’t start execution of thread in given place, but waits for it to terminate (or just returns, if it’s already terminated).