Skip to content

Yet another programming solutions log

Sample bits from programming for the future generations.

Technologies Technologies
  • Algorithms and Data Structures
  • Java Tutorials
  • JUnit Tutorial
  • MongoDB Tutorial
  • Quartz Scheduler Tutorial
  • Spock Framework Tutorial
  • Spring Framework
  • Bash Tutorial
  • Clojure Tutorial
  • Design Patterns
  • Developer’s Tools
  • Productivity
  • About
Expand Search Form

Generate random numbers concurrently – ThreadLocalRandom

farenda 2016-12-20 0

Until Java 7 there was no simple and effective way to generate random numbers concurrently. Here we show ThreadLocalRandom to generate random numbers in a thread-safe way.

One of the most notable additions in Java 7 was Fork Join Framework. But not many people know that it came with a bunch of classes useful in parallel computations. One of them is java.util.concurrent.ThreadLocalRandom. The class used in concurrent programs causes less overhead and contention than shared Random (which is not thread-safe as you probably know).

Thread safe random number generator

The usage of ThreadLocalRandom is pretty simple. We need to call current() static method to obtain a ThreadLocal version and then just obtain random numbers as usual. Here we use ints() from Java 8 to get stream of random ints and collect them into a List:

package com.farenda.java.util.concurrent;

import java.util.List;
import java.util.concurrent.ThreadLocalRandom;

import static java.util.stream.Collectors.toList;

public class ConcurrentRandomNumbers {

    public List<Integer> randomRange(int from, int howMany) {
        return ThreadLocalRandom.current()
                .ints(howMany, from, from+howMany)
                .boxed()
                .collect(toList());
    }
}

In the below program we’re going to use this method from concurrently executed tasks.

Generating random numbers in ranges

Task executed concurrently

Simple task that will request random numbers in range:

package com.farenda.java.util.concurrent;

import java.util.List;
import java.util.concurrent.Callable;

class ConcurrentRange implements Callable<List<Integer>> {

    private ConcurrentRandomNumbers generator;
    private final int from;
    private final int howMany;

    public ConcurrentRange(ConcurrentRandomNumbers generator,
                           int from, int howMany) {
        this.generator = generator;
        this.from = from;
        this.howMany = howMany;
    }

    @Override
    public List<Integer> call() throws Exception {
        // request random numbers for this thread:
        return generator.randomRange(from, howMany);
    }
}

Generate ranges of random numbers

We create three tasks to concurrently generate numbers in specified ranges and then just print the results:

package com.farenda.java.util.concurrent;

import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadLocalRandom;

import static java.util.Arrays.asList;
import static java.util.stream.Collectors.toList;

public class ConcurrentRandomNumbers {

    private List<Integer> randomRange(int from, int howMany) {
        return ThreadLocalRandom.current()
                .ints(howMany, from, from+howMany)
                .boxed()
                .collect(toList());
    }

    public static void main(String[] args) throws Exception {
        ConcurrentRandomNumbers generator = new ConcurrentRandomNumbers();

        ExecutorService es = Executors.newCachedThreadPool();

        List<ConcurrentRange> randomRanges = asList(
                new ConcurrentRange(generator, 10, 10),
                new ConcurrentRange(generator, 20, 10),
                new ConcurrentRange(generator, 30, 10));
        List<Future<List<Integer>>> results = es.invokeAll(randomRanges);

        for (Future<List<Integer>> future : results) {
            System.out.println("Range: " + future.get());
        }

        es.shutdown();
    }
}

Output of sample execution:

Range: [11, 16, 10, 10, 16, 13, 10, 11, 10, 18]
Range: [24, 25, 26, 22, 26, 26, 24, 29, 27, 24]
Range: [32, 30, 32, 30, 37, 31, 34, 30, 31, 36]

References:

  • Java random integers in range
  • Java ThreadLocal – thread data separation
Share with the World!
Categories Java Tags java, java-concurrency, java8
Previous: Insertion Sort in Clojure
Next: Clojure transients – fast mutations in persistent world

Recent Posts

  • Java 8 Date Time concepts
  • Maven dependency to local JAR
  • Caesar cipher in Java
  • Java casting trick
  • Java 8 flatMap practical example
  • Linked List – remove element
  • Linked List – insert element at position
  • Linked List add element at the end
  • Create Java Streams
  • Floyd Cycle detection in Java

Pages

  • About Farenda
  • Algorithms and Data Structures
  • Bash Tutorial
  • Bean Validation Tutorial
  • Clojure Tutorial
  • Design Patterns
  • Java 8 Streams and Lambda Expressions Tutorial
  • Java Basics Tutorial
  • Java Collections Tutorial
  • Java Concurrency Tutorial
  • Java IO Tutorial
  • Java Tutorials
  • Java Util Tutorial
  • Java XML Tutorial
  • JUnit Tutorial
  • MongoDB Tutorial
  • Quartz Scheduler Tutorial
  • Software Developer’s Tools
  • Spock Framework Tutorial
  • Spring Framework

Tags

algorithms bash bean-validation books clojure design-patterns embedmongo exercises git gof gradle groovy hateoas hsqldb i18n java java-basics java-collections java-concurrency java-io java-lang java-time java-util java-xml java8 java8-files junit linux lists log4j logging maven mongodb performance quartz refactoring regex rest slf4j solid spring spring-boot spring-core sql unit-tests

Yet another programming solutions log © 2021

sponsored
We use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it.Ok