Question

I have to do a benchmarking for performance difference between multi-threaded and multi-process architecture in java. This is the code i used to create new process

         for(int i=0;i<100;i++)
          {
            try {
                Process p = Runtime.getRuntime().exec("java -jar myjar.jar " + input);
            } catch (Exception e) {
                System.out.println("Exception in creating process");
                e.printStackTrace();
            }
          }

Is there a way to know when all the processes started by my main java program has finished execution?

Answer 1

Yes: call waitFor for each Process:

for (Process p: processes) // you must save your Process references somewhere :)
   p.waitFor(); 

If p is already finished the method returns inmediatly. If it’s not, it waits.

Edit: if you need to do other things in the mean time, execute this for/wait in another Thread. The thread will end the loop when all process are terminated, and you can do other things:

final List<Process> processes = new ArrayList<Process>();

// start processes
for (...) {
   p = ...
   processes.add(p);
}

// create and start "watchdog" thread
new Thread() {
   public void run() {
      for (p: processes) 
         p.waitFor();

      // at this point all processes are terminated
   }.start();

// ok, I've started the "watchdog" thread. now let's do fun stuff...

// do my stuff...