Groovy - Scheduling Threads

Groovy is a multi-threaded programming language where we can develop multi-threaded program using Groovy. A multi-threaded program contains two or more parts that can run concurrently and each part can handle a different task at the same time making optimal use of the available resources specially when your computer has multiple CPUs.

Multitasking vs Multithreading

Multitasking is when multiple processes share common processing resources such as a CPU. Multi-threading extends the idea of multitasking into applications where you can subdivide specific operations within a single application into individual threads. Each of the threads can run in parallel. The OS divides processing time not only among different applications, but also among each thread within an application.

Multi-threading enables you to write in a way where multiple activities can proceed concurrently in the same program.

Groovy uses a java.util.concurrent.ScheduledExecutorService interface which is a subinterface of ExecutorService interface, and supports future and/or periodic execution of tasks/threads. Following are few important and useful methods this interface.

ScheduledExecutorService Methods

Example - Scheduling a Task to run at Fixed Rate

The following TestThread program shows usage of ScheduledExecutorService interface in thread based environment to schedule a task to run after 2 seconds at interval of 2 seconds in time period of 10 seconds showcasing usage of scheduleAtFixedRate() and schedule() methods.

Example.groovy

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

class Example {
   static void main(final String[] arguments) throws InterruptedException {
      final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

      final ScheduledFuture<?> beepHandler = 
         scheduler.scheduleAtFixedRate(new BeepTask(), 2, 2, TimeUnit.SECONDS);

      scheduler.schedule(new Runnable() {
         @Override
         public void run() {
            beepHandler.cancel(true);
            scheduler.shutdown();			
         }
      }, 10, TimeUnit.SECONDS);
   }

   static class BeepTask implements Runnable {
      void run() {
         println("beep");      
      }
   }
}

Output

The above program produces the following output −

beep
beep
beep
beep
beep

Example - Scheduling a Task to run with Fixed Delay

The following TestThread program shows usage of ScheduledExecutorService interface in thread based environment to schedule a task to run after 2 seconds at interval of 2 seconds in time period of 10 seconds showcasing usage of scheduleWithFixedDelay() and schedule() methods.

Example.groovy

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

class Example {

   static void main(String[] args) throws InterruptedException {
      final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

      final ScheduledFuture<?> beepHandler = 
         scheduler.scheduleWithFixedDelay(new BeepTask(), 2, 2, TimeUnit.SECONDS);

      scheduler.schedule(new Runnable() {
         @Override
         public void run() {
            beepHandler.cancel(true);
            scheduler.shutdown();			
         }
      }, 10, TimeUnit.SECONDS);
   }

   static class BeepTask implements Runnable {     
      void run() {
         println("beep");      
      }
   }
}

Output

The above program produces the following output −

beep
beep
beep
beep

Example - Using schedule method to schedule threads

The following TestThread program shows usage of ScheduledExecutorService interface in thread based environment to schedule a task to run once after 2 seconds in time period of 10 seconds showcasing usage of schedule() method.

Example.groovy

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

class Example {

   static void main(String[] args) throws InterruptedException {
      final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

      final ScheduledFuture<?> beepHandler = 
         scheduler.schedule(new BeepTask(), 2, TimeUnit.SECONDS);

      scheduler.schedule(new Runnable() {

         @Override
         public void run() {
            beepHandler.cancel(true);
            scheduler.shutdown();			
         }
      }, 10, TimeUnit.SECONDS);
   }

   static class BeepTask implements Runnable {
      void run() {
         println("beep");      
      }
   }
}

Output

The above program produces the following output −

beep