Question

I have a for cylce that calls threads:

if(toModify[j]==1)
{
    getUpdate(methods_list[j],username, password);
}

getUpdate is a method which contains something like this:

new Thread(new Runnable() {
  public void run() {
      // *** some operations***
  }
}).start();

Through for cycle I can run each Thread simultaneously.
But if I want that each Thread starts only after the previous has stopped, can I use the following trick?

if(toModify[j]==1)
{
  int returnValue =  getUpdate(methods_list[j],username, password);
}

and add at the end of getUpdate method this code line (outside of run method):

return 1;

Using the above code each thread can start only if the previus has stopped? Or I’m wrong?

Answer 1

You can use RetrantLock

private final ReentrantLock lock = new ReentrantLock();

if(toModify[j]==1)        
  {   
      lock.lock();  // block until condition holds
 try {
   getUpdate(methods_list[j],username, password);         
 } finally {
   lock.unlock()
 }

} 

Also you will need to call join() on thread that is started from getUpdate() method.

Thread thread = new Thread(new Runnable() { 
        public void run() { 
        // *** some operations*** 
        } 
        }); 
    thread.start();
    thread.join();