Java Thread Fork/join Framework __java

The Fork/join framework is to solve the problem by using multithreading to realize the divide-and-conquer method. Fork refers to the problem of constantly narrowing the scale, join refers to the results of the calculation of the child problem, to obtain a higher level of results.

The use of the FORK/JOIN framework has certain constraints:

1. In addition to the fork () and join () methods, threads must not use other synchronization tools. Thread is best not to sleep ()

2. Threads must not do I/O operations

3. Threads must not throw checked exception

This framework has several core classes: Forkjoinpool is the thread pool that implements the work-stealing algorithm. Forkjointask is the task class, he has 2 subclasses: Recursiveaction no return value, Recursivetask has a return value, in the definition of their own tasks, usually from the 2 classes, the way to define their own new classes. Because the Forkjointask class implements the Serializable interface, the Serialversionuid attribute should be defined when defining its own task class.

When writing a task, the recommended wording is this:

[Java] view plain copy If (problem size > Default size) {Task s = divide (Task);   Execute (tasks);   else {resolve problem using another algorithm; }

Forkjoinpool implements the work-stealing algorithm (work-stealing), where threads proactively look for newly created tasks to execute to ensure higher threading utilization. It uses a daemon thread (Deamon) to perform the task, so it is not necessary to close the call shutdown () that he displays. In general, a program needs only one forkjoinpool, so it should be created as follows:

Static final Forkjoinpool Mainpool = new Forkjoinpool (); The number of threads equals the core number of CPUs

Here's a very simple example of a feature that adds 1 to the value of each element in an array. The implementation is: the large array is continuously decomposed into a shorter array, when the length of the sub-array is not more than 10, all elements of which are added 1 operations.

[Java]  View Plain  copy public class test {              public final static ForkJoinPool mainPool = new  Forkjoinpool ();              public static  void main (String[] args) {           int  n = 26;           int[] a = new  int[n];           for (int i=0; i<n; i + +)  {               a[i] =  i;           }            subtask task = new subtask (a, 0, n);             mainpool.invoke (Task);           for (int  i=0; i<n; i++)  {                system.out.print (a[i]+ " ");            }       }  }      class subtask extends  RecursiveAction {          private static final  long serialVersionUID = 1L;               private int[] a;       private int beg;        private int end;               public subtask (int[] a, int beg, int end)  {     &nbsP;     super ();   &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;THIS.A  = a;           this.beg = beg;            this.end = end;        }           @Override        protected  void compute ()  {           if