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What is the forkjoin framework in the concurrent programming series?
2022-07-01 15:43:00 【51CTO】
What is concurrent programming ForkJoin frame ？
1、 What is? ForkJoin frame
ForkJoin The frame is java Of JUC It's in the bag , Used to handle some heavy tasks , Will divide this big task into several small tasks , After multiple small tasks are processed, the results will be summarized to Result, It embodies a kind of “ Divide and rule ” Thought . First step , Split fork Mission , Divide large tasks into small tasks ; The second step , Merger join, The processing results of small tasks will be merged into one result .
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2、ForkJoinTask
ForkJoinTask yes ForkJoin Tasks provided by the framework API,ForkJoinTask Is an abstract class , There are two main implementation classes ,RecursiveTask and RecursiveAction, among RecursiveTask and RecursiveAction The main difference is ,RecursiveAction no return value , and RecursiveTask There is a return value
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3、ForkJoinPool
ForkJoinPool Class is forkjoin The thread pool implementation of the framework , be based on ExecutorService Interface . This thread pool is jdk1.7 Just joined in , For managing threads , perform forkjoin The task of . For the use of thread pools , We use ThreadPoolExecutor More , Can be in idea Take a look inside uml Class diagram , It can be seen that ForkJoinPool and ThreadPoolExecutor Achieve almost .
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Several important parameters ：
- parallelism： Parallelism , Parallel execution threads , You can specify , Or not , Not specified , It's based on cpu The core creates available threads
- ForkJoinWorkerThreadFactory： Create a factory implementation of threads
- UncaughtExceptionHandler ： Callback processing for unknown exception interrupt
- asyncMode： Asynchronous or not , The default is false
When using , Can be created directly ForkJoinPool, It's OK not to pass on the parameters , If you don't pass the parameters , The number of thread parallelism specified by default is Runtime.getRunTime().availableProcessors();, Express basis cpu Number of threads available for core creation
It can also be used to pass parameters , Specifies the degree of parallelism public ForkJoinPool(int parallelism), parallelism Parallelism , Execute several threads in parallel
take forkjoin Add tasks to FrokJoinPool There are several ways to thread pool
- execute()： Call its fork Method splits work between multiple threads .
- invoke()： stay ForkJoinPool Call... On the thread pool invoke Method
- submit()： Return to one Future object ,Future Can be monitored , After the task is completed, the result is returned
4、 Print Fibonacci series
ForkJoin The framework can be used in some recursive traversal scenarios , For Fibonacci series , You can be familiar with , Because sometimes I often ask , The characteristic of Fibonacci sequence is that the result of the last term is equal to the sum of the first two terms
package com.example.concurrent.forkjoin;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
/**
* <pre>
* Fibonacci sequence
* </pre>
* <p>
* <pre>
* @author nicky.ma
* Modify the record
* Revised version : Modifier ： modification date : 2021/10/12 16:22 Modify the content :
* </pre>
*/
public class Fibonacci extends RecursiveTask<Integer>{
private int n;
public Fibonacci(int n) {
this.n = n;
}
@Override
protected Integer compute() {
if (n <= 1)
return n;
Fibonacci f1 = new Fibonacci(n - 1);
f1.fork();
Fibonacci f2 = new Fibonacci(n - 2);
f2.fork();
return f1.join() + f2.join();
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
ForkJoinPool pool = new ForkJoinPool();
for (int i = 0; i< 10; i++) {
ForkJoinTask task = pool.submit(new Fibonacci(i));
System.out.println(task.get());
}
}
}
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5、ForkJoin Merge sort
Interview questions ： Quickly sort an array with a length of millions
difficulty ： You can use merge sort , How do multithreads organize and implement merge sorting
package com.example.concurrent.forkjoin;
import java.util.Arrays;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
/**
* <pre>
* Large array sort
* </pre>
* <p>
* <pre>
* @author mazq
* Modify the record
* Revised version : Modifier ： modification date : 2021/10/12 17:04 Modify the content :
* </pre>
*/
public class ArraySortTask extends RecursiveAction{
final long[] array; final int lo, hi;
ArraySortTask(long[] array, int lo, int hi) {
this.array = array; this.lo = lo; this.hi = hi;
}
ArraySortTask(long[] array) { this(array, 0, array.length); }
@Override
protected void compute() {
if (hi - lo < THRESHOLD)
// Less than threshold , Use Arrays.sort Quick line up
sortSequentially(lo, hi);
else {
/* Merge sort */
// Median value
int mid = (lo + hi) >>> 1;
// Split the task
invokeAll(new ArraySortTask(array, lo, mid),
new ArraySortTask(array, mid, hi));
// The result of amalgamation
merge(lo, mid, hi);
}
}
// implementation details follow:
static final int THRESHOLD = 1000;
void sortSequentially(int lo, int hi) {
Arrays.sort(array, lo, hi);
}
void merge(int lo, int mid, int hi) {
long[] buf = Arrays.copyOfRange(array, lo, mid);
for (int i = 0, j = lo, k = mid; i < buf.length; j++)
array[j] = (k == hi || buf[i] < array[k]) ?
buf[i++] : array[k++];
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
int size = 10_000;
long[] array = new long[size];
Random random = new Random();
for (int i = 0; i< size; i++) {
array[i] = random.nextInt();
}
ForkJoinPool forkJoinPool = new ForkJoinPool();
ArraySortTask task = new ArraySortTask(array , 0 , size);
forkJoinPool.submit(task);
task.get();
for (long a : array) {
System.out.println(a);
}
}
}
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