another thread question

[arie zwijnsma]

suppose 2 threads are concurrently using the same integer m_i.
as in m_i++; or if ( m_i == 1 ) or j = m_i%2==0?m_i:-1
i am wondering are these statements thread safe 'on their own' ???
i mean is it possible that the os switches to the 2nd thread when
the 1st thread has not yet finished the statement it was working on ?
(see also code below)
thanks arie.

public class A extends Thread {
  static int m_i;
  public static void main(String args[]){
    (new A()).start();
    (new A()).start();
  }
  public void run() {
    while(true) {
      //is this thread safe ?
       m_i++;
      // or should i use ?
      safe_inc();
    
    }
  }
  static synchronized int safe_inc() {
    return m_i++;
  }
}

[tvs sundaram]

volatile.??!!!

[Manfred Leonhardt]

Hi Arie,
I would say that the statements ARE NOT thread safe because it is quite possible for a time-sharing thread handler to remove one thread when its' time is up and it has not completely finsihed the statement. Since thread handling is up to each vendor you can never be completely sure what will happen to threads.
Regards,
Manfred.