如果一个结果为假，请停止多个FutureTask

Question

这个程序出了什么问题？如果其中一个结果返回false，我想立即停止所有FutureTask。参见第100行及以下内容。我有一份未来任务的清单。然后我实例化一个executor服务并添加所有任务。然后，我执行任务并遍历任务列表，以检查一个任务是否返回false。

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
public class PrimeIterator {
private boolean longBased = true;
private long startLong;
private BigInteger startBI;
public PrimeIterator(BigInteger start) {
if (start.compareTo(BigInteger.valueOf(Long.MAX_VALUE)) > 0) {
longBased = false;
}
if (longBased) {
startLong = start.longValue();
} else {
startBI = start;
}
}
public BigInteger nextPrime() {
BigInteger b;
while (true) {
if (longBased) {
if (isPrime(startLong)) {
b = BigInteger.valueOf(startLong);
increase();
return b;
}
} else {
if (isPrime(startBI)) {
b = startBI;
increase();
return b;
}
}
increase();
}
}
private boolean isPrime(long toTest) {
if (toTest % 2 == 0) {
return false;
}
long sqrt = (long) Math.sqrt(startLong);
for (long i = 3; i <= sqrt; i += 2) {
if (toTest % i == 0) {
return false;
}
}
return true;
}
private static class MyTask implements Callable<Boolean> {
private final BigInteger toTest;
private final BigInteger part;
private final int multiplier;
private static volatile boolean hasFalseResult;
private MyTask(BigInteger toTest, BigInteger part, int multiplier) {
this.toTest = toTest;
this.part = part;
this.multiplier = multiplier;
hasFalseResult = false;
}
@Override
public Boolean call() throws Exception {
BigInteger from = part.multiply(BigInteger.valueOf(multiplier)).add(BigInteger.valueOf(3));
BigInteger to = part.multiply(BigInteger.valueOf(multiplier + 1)).add(BigInteger.valueOf(3));
System.out.println("starting: " + toTest + " " + from + " " + to + " " + toTest.sqrt());
return isPrime(toTest, from, to);
}
private boolean isPrime(BigInteger b, BigInteger from, BigInteger to) {
for (BigInteger i = from; to.compareTo(i) > 0; i = i.add(BigInteger.TWO)) {
if (hasFalseResult) {
return false;
}
if (b.mod(i).compareTo(BigInteger.ZERO) == 0) {
hasFalseResult = true;
return false;
}
}
return true;
}
}
private boolean isPrime(BigInteger toTest) {
// if (toTest.isProbablePrime(5)) {
if (toTest.mod(BigInteger.TWO).compareTo(BigInteger.ZERO) == 0) {
return false;
}
BigInteger sqrt = toTest.sqrt();
BigInteger part = sqrt.divide(BigInteger.valueOf(10)).add(BigInteger.ONE);
List<FutureTask<Boolean>> taskList = new ArrayList<FutureTask<Boolean>>();
for (int i = 0; i < 10; i++) {
taskList.add(new FutureTask<>(new MyTask(toTest, part, i)));
}
ExecutorService executor = Executors.newFixedThreadPool(3);
for (FutureTask<Boolean> futureTask : taskList) {
executor.execute(futureTask);
}
try {
for (FutureTask<Boolean> futureTask : taskList) {
if (!futureTask.get()) {
return false;
}
}
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
return false;
}
return true;
// }
// return false;
}
private void increase() {
if (longBased) {
if (startLong == Long.MAX_VALUE) {
longBased = false;
startBI = BigInteger.valueOf(Long.MAX_VALUE).add(BigInteger.ONE);
} else {
startLong++;
}
} else {
startBI = startBI.add(BigInteger.ONE);
}
}
public static void main(String[] args) {
PrimeIterator pi = new PrimeIterator(BigInteger.valueOf(1));
for (int i = 0; i < 20; i++) {
System.out.println(pi.nextPrime());
}
pi = new PrimeIterator(BigInteger.valueOf(Long.MAX_VALUE - 10));
for (int i = 0; i < 5; i++) {
System.out.println(pi.nextPrime());
}
}
}

Answer 1

FutureTasks在后台线程中运行。一旦返回false，isPrime()方法将立即返回。但它不会阻止其他FutureTask完成，因为它们在单独的线程中运行。