Module java.base

Class RecursiveTask<V>

java.lang.Object
java.util.concurrent.ForkJoinTask<V>
java.util.concurrent.RecursiveTask<V>
All Implemented Interfaces:
Serializable, Future<V>

public abstract class RecursiveTask<V> extends ForkJoinTask<V>
A recursive result-bearing ForkJoinTask.

For a classic example, here is a task computing Fibonacci numbers:

 
 class Fibonacci extends RecursiveTask<Integer> {
   final int n;
   Fibonacci(int n) { this.n = n; }
   protected Integer compute() {
     if (n <= 1)
       return n;
     Fibonacci f1 = new Fibonacci(n - 1);
     f1.fork();
     Fibonacci f2 = new Fibonacci(n - 2);
     return f2.compute() + f1.join();
   }
 }
However, besides being a dumb way to compute Fibonacci functions (there is a simple fast linear algorithm that you'd use in practice), this is likely to perform poorly because the smallest subtasks are too small to be worthwhile splitting up. Instead, as is the case for nearly all fork/join applications, you'd pick some minimum granularity size (for example 10 here) for which you always sequentially solve rather than subdividing.

Since:
1.7
See Also:
Serialized Form
  • Constructor Details

    • RecursiveTask

      public RecursiveTask()
      Constructor for subclasses to call.
  • Method Details

    • compute

      protected abstract V compute()
      The main computation performed by this task.
      Returns:
      the result of the computation
    • getRawResult

      public final V getRawResult()
      Description copied from class: ForkJoinTask
      Returns the result that would be returned by ForkJoinTask.join(), even if this task completed abnormally, or null if this task is not known to have been completed. This method is designed to aid debugging, as well as to support extensions. Its use in any other context is discouraged.
      Specified by:
      getRawResult in class ForkJoinTask<V>
      Returns:
      the result, or null if not completed
    • setRawResult

      protected final void setRawResult(V value)
      Description copied from class: ForkJoinTask
      Forces the given value to be returned as a result. This method is designed to support extensions, and should not in general be called otherwise.
      Specified by:
      setRawResult in class ForkJoinTask<V>
      Parameters:
      value - the value
    • exec

      protected final boolean exec()
      Implements execution conventions for RecursiveTask.
      Specified by:
      exec in class ForkJoinTask<V>
      Returns:
      true if this task is known to have completed normally