我試圖執行一個簡單的計算(它調用Math.random()
10000000次)。令人驚訝的是,使用簡單方法運行它比使用ExecutorService要快得多。ExecutorService緩慢多線程性能
我已閱讀另一個線程ExecutorService's surprising performance break-even point --- rules of thumb?,並試圖遵循執行Callable
使用批次的答案,但表現依然糟糕
如何提高性能的基礎上我當前的代碼?
import java.util.*;
import java.util.concurrent.*;
public class MainTest {
public static void main(String[]args) throws Exception {
new MainTest().start();;
}
final List<Worker> workermulti = new ArrayList<Worker>();
final List<Worker> workersingle = new ArrayList<Worker>();
final int count=10000000;
public void start() throws Exception {
int n=2;
workersingle.add(new Worker(1));
for (int i=0;i<n;i++) {
// worker will only do count/n job
workermulti.add(new Worker(n));
}
ExecutorService serviceSingle = Executors.newSingleThreadExecutor();
ExecutorService serviceMulti = Executors.newFixedThreadPool(n);
long s,e;
int tests=10;
List<Long> simple = new ArrayList<Long>();
List<Long> single = new ArrayList<Long>();
List<Long> multi = new ArrayList<Long>();
for (int i=0;i<tests;i++) {
// simple
s = System.currentTimeMillis();
simple();
e = System.currentTimeMillis();
simple.add(e-s);
// single thread
s = System.currentTimeMillis();
serviceSingle.invokeAll(workersingle); // single thread
e = System.currentTimeMillis();
single.add(e-s);
// multi thread
s = System.currentTimeMillis();
serviceMulti.invokeAll(workermulti);
e = System.currentTimeMillis();
multi.add(e-s);
}
long avgSimple=sum(simple)/tests;
long avgSingle=sum(single)/tests;
long avgMulti=sum(multi)/tests;
System.out.println("Average simple: "+avgSimple+" ms");
System.out.println("Average single thread: "+avgSingle+" ms");
System.out.println("Average multi thread: "+avgMulti+" ms");
serviceSingle.shutdown();
serviceMulti.shutdown();
}
long sum(List<Long> list) {
long sum=0;
for (long l : list) {
sum+=l;
}
return sum;
}
private void simple() {
for (int i=0;i<count;i++){
Math.random();
}
}
class Worker implements Callable<Void> {
int n;
public Worker(int n) {
this.n=n;
}
@Override
public Void call() throws Exception {
// divide count with n to perform batch execution
for (int i=0;i<(count/n);i++) {
Math.random();
}
return null;
}
}
}
輸出此代碼
Average simple: 920 ms
Average single thread: 1034 ms
Average multi thread: 1393 ms
編輯:性能遭受由於的Math.random()是一個同步的方法。與新Random對象改變的Math.random()爲每個線程之後中,性能改進
輸出爲新的代碼(具有隨機取代的Math.random()爲每個線程之後)
Average simple: 928 ms
Average single thread: 1046 ms
Average multi thread: 642 ms
啊,你是對的!我沒有意識到Math.random()是同步的。一旦我爲每個Worker添加了新的Random對象,性能就大大提高了 – GantengX
只是一個簡單的問題,如果我試圖共享Random對象,性能仍會受到影響。你知道這是爲什麼嗎? Random.nextDouble不同步,它調用Random.next(int),後者又調用AtomicLong.compareAndSet ..我不明白爲什麼這會影響性能 – GantengX
我猜想,因爲你只是回到讓多個線程再次爭用相同的資源:在這種情況下的AtomicLong。一次只有一個線程可以更新其值,並且每次調用nextDouble()時都會更新兩次。 –