ForkJoinFramework

The fork/join framework provides a very straightforward and intuitive structure to implement recursive and divide and conquer problems that can be solved concurrently. You start with the big problem and break it down in smaller work units until each work unit can be solved directly.
The algorithm takes this form:

Result solve(Problem problem) {
  if (problem is small)
    directly solve problem
  else {
    split problem into independent parts
    fork new subtasks to solve each part
    join all subtasks
    compose result from subresults
  }
}

As the ForkJoin Framework is standard in Java 8 and Java 7, you can view the official documentation here and the javadoc for all subclasses in the ForkJoin framework here.

Task parallelism / Functional parallelism

Task parallelism focuses on distributing tasks concurrently and execute those tasks by processes or threads across different processors. You can consider the fork/join framework if you want to perform some task parallelism on your project. Thus dividing each your program into asynchronous tasks operating in parallel.

There are only 2-4 classes you need to know about to perform parallel tasks:

• ForkJoinPool: An instance of this class is used to run all your fork-join tasks in the whole program.
• RecursiveTask(V): You run a subclass of this in a pool and have it return a result.
• RecursiveAction: just like RecursiveTask except it does not return a result
• ForkJoinTask(V): superclass of RecursiveTask and RecursiveAction. fork and join are methods defined in this class.

In this Repo:

• SumArray: performing the sum of an array in sequentail & in parallel (using ForkJoin framework) and calculating the overall speedup.
• MergeSort: parallel merge sort, with calculating the total speedup between regular merge sort & parallel merge sort.