How to run parallel python scripts from java using the ProcessBuilder

Question

this is my first question here. I am trying to run parallel python scripts (that is multiple instances of a same script) from java periodically using the ScheduledThreadPoolExecutor. What i tried to do was using the ProcessBuilder class. To test the concept i have put first script into infinite loop while the second writes something to file and exits. Python scripts i need to make should be identical to each other so i tried to run these two from multiple instaces of a same class that implements runnable.

However the second script never starts. I managed to solve this by creating many classes that have exactly same runnable. But it seems highly impractical to have 10-20 classes that are same. So can i do this somehow within one runnable? Here is the code that shows how i tried to run scripts using the ProcessBuilder:

public class TestScripts{

public static void main(String[] args){
       ScheduledThreadPoolExecutor threadPool = new ScheduledThreadPoolExecutor(2);
       threadPool.scheduleAtFixedRate(new MyTask1(), 1,2, TimeUnit.SECONDS);
       threadPool.scheduleAtFixedRate(new MyTask1(), 1,2, TimeUnit.SECONDS);
        }
  }


class MyTask1 implements Runnable{
public void run(){
     System.out.println("Task1 is running");
     ProcessBuilder processBuilder = new ProcessBuilder("C:\\Python27\\python.exe",
                                                        "C:\\Python27\\test.py");
     ProcessBuilder processBuilder2 = new ProcessBuilder("C:\\Python27\\python.exe",
                                                           "C:\\Python27\\test2.py");
    processBuilder.redirectOutput(Redirect.INHERIT);

    try {
        Process process = processBuilder.start();
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    try {
        Process process2 = processBuilder.start();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}
}

pajton · Accepted Answer · 2014-02-28 09:58:23Z

1

There is a typo in the line starting 2nd process:

Process process2 = processBuilder.start();

should be of course:

Process process2 = processBuilder2.start();

Besides you are scheduling 2 tasks, where each task starts 2 processes. So each 2 seconds there are 4 processes started (2x test.py, 2x test2.py). If I understand correctly what you're trying to do, scheduling only one MyTask1 should be enough.

answered Feb 28, 2014 at 9:58

pajton

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1 Comment

John Over a year ago

Ohh, that was exactly the cause of problem. didn't notice the typo! I needed to schedule n number of worker threads from the thread pool where each thread runs same script few times before next period. Thank you sir

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