在subtask.fork()返回ForkJoinTask<Int>
个对象后会发生什么?之后多次调用compute()方法但是从哪里以及如何调用?
我是Java的新手,我正在尝试学习fork / join框架的概念。我在网上看到了下面的代码。我知道在阅读Java API后,subtask.fork()
返回ForkJoinTask<V>
的对象,在这种情况下为ForkJoinTask<Int>
。我无法理解的是之后会发生什么?输出表明compute()
方法在此之后已被多次调用,但是从哪里以及如何调用?
public class MyRecursiveAction extends RecursiveAction {
public static void main(String[] args) {
MyRecursiveAction mra1 = new MyRecursiveAction(100);
ForkJoinPool fjp1 = new ForkJoinPool();
fjp1.invoke(mra1);
}
private long workLoad = 0;
public MyRecursiveAction(long workLoad) {
this.workLoad = workLoad;
}
@Override
protected void compute() {
//if work is above threshold, break tasks up into smaller tasks
if(this.workLoad > 16) {
System.out.println("Splitting workLoad : " + this.workLoad);
List<MyRecursiveAction> subtasks =
new ArrayList<MyRecursiveAction>();
subtasks.addAll(createSubtasks());
for(RecursiveAction subtask : subtasks){
subtask.fork();
}
} else {
System.out.println("Doing workLoad myself: " + this.workLoad);
}
}
private List<MyRecursiveAction> createSubtasks() {
List<MyRecursiveAction> subtasks =
new ArrayList<MyRecursiveAction>();
MyRecursiveAction subtask1 = new MyRecursiveAction(this.workLoad / 2);
MyRecursiveAction subtask2 = new MyRecursiveAction(this.workLoad / 2);
subtasks.add(subtask1);
subtasks.add(subtask2);
return subtasks;
}
}
输出:
Splitting workLoad : 100
Splitting workLoad : 50
Splitting workLoad : 50
Splitting workLoad : 25
Doing workLoad myself: 12
Doing workLoad myself: 12
Splitting workLoad : 25
Doing workLoad myself: 12
Doing workLoad myself: 12
Splitting workLoad : 25
Doing workLoad myself: 12
Splitting workLoad : 25
Doing workLoad myself: 12
Doing workLoad myself: 12
Doing workLoad myself: 12
答案 0 :(得分:1)
你需要调用invokeAll,以便将你的工作分成两部分而不是手工完成,然后创建2个新的线程来计算&#39;你的结果,如果它不够小2个新线程等等,
您无法预测线程的执行顺序,因此每次运行此代码时,消息顺序都会有所不同。
CREATE TABLE STUDENT
(sID INTEGER PRIMARY KEY NOT NULL,
sFName VARCHAR(20),
sLName VARCHAR(20));
CREATE TABLE COURSE
(cID VARCHAR(20) PRIMARY KEY NOT NULL,
cName VARCHAR(20),
cr INTEGER);
CREATE TABLE PROF
(pID INTEGER PRIMARY KEY NOT NULL,
pFName VARCHAR(20),
pLName VARCHAR(20));
CREATE TABLE ENROLLED
(sID INTEGER NOT NULL,
cID VARCHAR(20) NOT NULL,
PRIMARY KEY (sID, cID),
FOREIGN KEY (sID) REFERENCES STUDENT,
FOREIGN KEY (cID) REFERENCES COURSE);
CREATE TABLE TEACHING
(pID INTEGER NOT NULL,
cID VARCHAR(20) NOT NULL,
PRIMARY KEY (pID, cID),
FOREIGN KEY (pID) REFERENCES PROF,
FOREIGN KEY (cID) REFERENCES COURSE);