Java8 병렬처리 프로그램 성능분석

- 단순계산을 parallel 프로그래밍 하면 오히려 더 느려짐.(아래 코드에서 peek() 부분을 빼고 실행해보면 됨)

public class ParallelPerformanceExcamples1 {

public static void main(String[] args) {

// final long n = 10_000_000;

final long n = 1000;

// System.out.println((1+n)*(n/2)); //가우스 수식

final long start1 = System.currentTimeMillis();

System.out.println("iterativeSum:" + iterativeSum(n));

System.out.println("elapsed " + (System.currentTimeMillis()-start1) + " ms.\n");

final long start2 = System.currentTimeMillis();

System.out.println("sequentialSum:" + sequentialSum(n));

System.out.println("elapsed " + (System.currentTimeMillis()-start2) + " ms.\n");

final long start3 = System.currentTimeMillis();

System.out.println("parallelSum:" + parallelSum(n));

System.out.println("elapsed " + (System.currentTimeMillis()-start3) + " ms.\n");

final long start4 = System.currentTimeMillis();

System.out.println("rangedSum:" + rangedSum(n));

System.out.println("elapsed " + (System.currentTimeMillis()-start4) + " ms.\n");

final long start5 = System.currentTimeMillis();

System.out.println("parallelRangedSum:" + parallelRangedSum(n));

System.out.println("elapsed " + (System.currentTimeMillis()-start5) + " ms.\n");

}

public static long iterativeSum(long n){

long result = 0;

for(long i = 0; i <= n; i++){

result += i; 

slowDown();

}

return result;

}

public static long sequentialSum(long n){

return Stream.iterate(1L, i -> i + 1).limit(n).peek(i->slowDown()).reduce(Long::sum).get();

}

public static long parallelSum(long n){

//단순계산은 parallel처리 시 더 오래 걸림.

//reduce는 초기값이 필요한데 병렬처리 시 초기값을 알 수 있을 때가지 기다려야 하므로 더 느려짐.

return Stream.iterate(1L, i -> i + 1).limit(n).parallel().peek(i->slowDown()).reduce(Long::sum).get();

}

public static long rangedSum(long n){

return LongStream.rangeClosed(1, n).peek(i->slowDown()).reduce(Long::sum).getAsLong();

}

public static long parallelRangedSum(long n){

return LongStream.rangeClosed(1, n).parallel().peek(i->slowDown()).reduce(Long::sum).getAsLong();

}

public static void slowDown(){

try {

TimeUnit.MILLISECONDS.sleep(10L);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

위 결과.

iterativeSum:500500

elapsed 10082 ms.

sequentialSum:500500

elapsed 10209 ms.

parallelSum:500500

elapsed 2521 ms.

rangedSum:500500

elapsed 10033 ms.

parallelRangedSum:500500

elapsed 2535 ms.