Первая часть — разбор самой холиварной задачи из четырёх:
void forEach(List<Integer> values, PrintStream ps) {
values.forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
Под катом условие задач, история их появления, а также разбор первой задачи и статистика её правильных решений среди участников конференции.
Предисловие
Коллега за десять дней до конференции пришёл с предложением подготовить задачи для розыгрыша призов, где топовыми призами стали бы несколько книг Effective Java от Джошуа Блоха (последнее третье издание). Под такие призы нужны соответствующие задачи. И так, вызов принят.
Для начала определимся, что мы хотим получить:
- задачи должны быть на код (я не мастер придумывать логические задачи, а брать готовые не хотелось)
- в задачах должен быть очевидный неправильный ответ
- задачи не должны быть все простыми или все сложными
- если закодить задачу, то это не должно дать 100% ответа, но может помочь в поиске верного решения
- в идеале задачи должны «зацепить», чтобы после конференции было желание докопаться до истины.
Так я решился подготовить задачи про перформанс в следующем виде:
- несколько вариантов алгоритмов, делающих что-то похожее
- требуется упорядочить их по скорости работы
- и объяснить, почему алгоритмы упорядочены именно таким образом.
Задачи
Комментарий ко всем задачам:
- Упорядочить методы по скорости их работы и вписать номера методов в соответствующую ячейку.
- Если методы дают незначительно отличающиеся результаты, тогда вписать их в одну ячейку.
- По каждой задаче написать разъяснение, почему одни методы быстрее других.
void forEach(List<Integer> values, PrintStream ps) {
values.forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
String format(String user, String grade, String company, String message) {
return String.format(
"Он, %s, придумал такие %s задачи. Приду на стенд %s и скажу ему %s",
user, grade, company, message);
}
String format(String user, String grade, String company, String message) {
return "Он, " + user
+ ", придумал такие " + grade
+ " задачи. Приду на стенд " + company
+ " и скажу ему " + message;
}
String format(String user, String grade, String company, String message) {
return new StringBuilder("Он, ")
.append(user)
.append(", придумал такие ")
.append(grade)
.append(" задачи. Приду на стенд ")
.append(company)
.append(" и скажу ему ")
.append(message)
.toString();
}
public static double compute(
double x1, double y1, double z1,
double x2, double y2, double z2) {
double x = y1 * z2 - z1 * y2;
double y = z1 * x2 - x1 * z2;
double z = x1 * y2 - y1 * x2;
return x * x + y * y + z * z;
}
public static double compute(
double x1, double y1, double z1,
double x2, double y2, double z2) {
Vector v1 = new Vector(x1, y1, z1);
Vector v2 = new Vector(x2, y2, z2);
return v1.crossProduct(v2).squared();
}
public final static class Vector {
private final double x, y, z;
public Vector(double x, double y, double z) {
this.x = x; this.y = y; this.z = z;
}
public double squared() {
return x * x + y * y + z * z;
}
public Vector crossProduct(Vector v) {
return new Vector(
y * v.z - z * v.y,
z * v.x - x * v.z,
x * v.y - y * v.x);
}
}
public double octaPow(double a) {
return Math.pow(a, 8);
}
public double octaPow(double a) {
return a * a * a * a * a * a * a * a;
}
public double octaPow(double a) {
return Math.pow(Math.pow(Math.pow(a, 2), 2), 2);
}
public double octaPow(double a) {
a *= a; a *= a; return a * a;
}
Предполагается, что код запускается в HotSpot 64-bit VM (JRE 1.8.0_161). В выбранной версии JRE нет ничего специфического, кроме того, что она одна из последних и уже у меня стояла — разумеется, что все задачи я должен был заранее проверить.
Неявно предполагается, что код запускается на многоядерном железе с архитектурой intel 64 (x86-64). Возможно, стоило это указать явно, но и дополнительные условия могли ввести в заблуждение. При этом, если пояснение к ответу в задаче учитывало специфику другого железа, то решение бы засчитывалось.
Задача №1
«foreach — это быстро», «Стримы тормозят», «Параллельно значит быстро» частенько доносилось из обсуждений Stream API, которому вот уже стукнет 4 года (если считать с даты публичного релиза Java 8). Так и я поддался пошёл на провокацию:
void forEach(List<Integer> values, PrintStream ps) {
values.forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
void forEach(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
Очевидный неправильный ответ: 3 вариант самый быстрый.
У многих сработал триггер «Параллельно значит быстро» и они попали в ловушку с PrintStream
.
Фрагмент исходного кода PrintStream
:
public void println(Object x) {
String s = String.valueOf(x);
synchronized (this) {
print(s);
newLine();
}
}
На практике это означает, что никакой выгоды от параллельного выполнения мы не получим независимо от размеров списка values
. Напротив, мы получим деградацию производительности, так как виртуальной машине придётся постоянно разруливать множественные блокировки на PrintStream
.
List.stream().forEach()
vs List.parallelStream().forEach()
Ниже бенчмарк для сравнения обычного последовательного и параллельного Stream
.
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0)
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.MICROSECONDS)
@BenchmarkMode(Mode.AverageTime)
public class StreamDefaultBenchmark {
static int N = 1000;
static List<Integer> values;
static {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@State(value = Scope.Benchmark)
public static class PrintStreamHolder {
PrintStream ps;
@Setup(value = Level.Iteration)
public void setup() {
ps = new PrintStream(new NullOutputStream());
}
}
@Benchmark
public void forEachStreamBenchmark(PrintStreamHolder psh) {
forEachStream(values, psh.ps);
}
@Benchmark
public void forEachParallelStreamBenchmark(PrintStreamHolder psh) {
forEachParallelStream(values, psh.ps);
}
public void forEachStream(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
public void forEachParallelStream(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamDefaultBenchmark.forEachParallelStreamBenchmark
# Run progress: 0,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 905,302 us/op
# Warmup Iteration 2: 876,525 us/op
# Warmup Iteration 3: 921,153 us/op
# Warmup Iteration 4: 898,899 us/op
# Warmup Iteration 5: 873,496 us/op
Iteration 1: 920,439 us/op
Iteration 2: 894,216 us/op
Iteration 3: 917,930 us/op
Iteration 4: 906,970 us/op
Iteration 5: 929,685 us/op
Iteration 6: 883,136 us/op
Iteration 7: 883,996 us/op
Iteration 8: 882,597 us/op
Iteration 9: 921,612 us/op
Iteration 10: 885,576 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamDefaultBenchmark.forEachParallelStreamBenchmark":
902,616 ±(99.9%) 28,296 us/op [Average]
(min, avg, max) = (882,597, 902,616, 929,685), stdev = 18,716
CI (99.9%): [874,320, 930,911] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamDefaultBenchmark.forEachStreamBenchmark
# Run progress: 50,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 285,837 us/op
# Warmup Iteration 2: 265,208 us/op
# Warmup Iteration 3: 157,321 us/op
# Warmup Iteration 4: 157,447 us/op
# Warmup Iteration 5: 157,689 us/op
Iteration 1: 157,192 us/op
Iteration 2: 161,511 us/op
Iteration 3: 161,464 us/op
Iteration 4: 156,948 us/op
Iteration 5: 158,526 us/op
Iteration 6: 163,035 us/op
Iteration 7: 159,140 us/op
Iteration 8: 158,476 us/op
Iteration 9: 158,884 us/op
Iteration 10: 159,072 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamDefaultBenchmark.forEachStreamBenchmark":
159,425 ±(99.9%) 2,976 us/op [Average]
(min, avg, max) = (156,948, 159,425, 163,035), stdev = 1,969
CI (99.9%): [156,448, 162,401] (assumes normal distribution)
# Run complete. Total time: 00:01:00
Benchmark Mode Cnt Score Error Units
StreamDefaultBenchmark.forEachParallelStreamBenchmark avgt 10 902,616 ± 28,296 us/op
StreamDefaultBenchmark.forEachStreamBenchmark avgt 10 159,425 ± 2,976 us/op
Понятно, что при однопоточном исполнении блокировка никуда не девается. Но виртуальная машина может поступать достаточно хитро, а именно не делать настоящую (на уровне OS) блокировку, а ограничиваться так называемой biased locking, если отсутствует contention на ресурсе.
Можем отключить biased locking и посмотреть, что получится:
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0, jvmArgsAppend = "-XX:-UseBiasedLocking")
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.MICROSECONDS)
@BenchmarkMode(Mode.AverageTime)
public class StreamWithoutBiasedLockingBenchmark {
static int N = 1000;
static List<Integer> values;
static {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@State(value = Scope.Benchmark)
public static class PrintStreamHolder {
PrintStream ps;
@Setup(value = Level.Iteration)
public void setup() {
ps = new PrintStream(new NullOutputStream());
}
}
@Benchmark
public void forEachStreamBenchmark(PrintStreamHolder psh) {
forEachStream(values, psh.ps);
}
@Benchmark
public void forEachParallelStreamBenchmark(PrintStreamHolder psh) {
forEachParallelStream(values, psh.ps);
}
public void forEachStream(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
public void forEachParallelStream(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: -XX:-UseBiasedLocking
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithoutBiasedLockingBenchmark.forEachParallelStreamBenchmark
# Run progress: 0,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 754,310 us/op
# Warmup Iteration 2: 723,277 us/op
# Warmup Iteration 3: 682,845 us/op
# Warmup Iteration 4: 696,635 us/op
# Warmup Iteration 5: 690,811 us/op
Iteration 1: 702,129 us/op
Iteration 2: 729,542 us/op
Iteration 3: 689,514 us/op
Iteration 4: 716,482 us/op
Iteration 5: 734,766 us/op
Iteration 6: 684,455 us/op
Iteration 7: 682,483 us/op
Iteration 8: 706,857 us/op
Iteration 9: 690,011 us/op
Iteration 10: 694,427 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithoutBiasedLockingBenchmark.forEachParallelStreamBenchmark":
703,067 ±(99.9%) 28,058 us/op [Average]
(min, avg, max) = (682,483, 703,067, 734,766), stdev = 18,559
CI (99.9%): [675,008, 731,125] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: -XX:-UseBiasedLocking
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithoutBiasedLockingBenchmark.forEachStreamBenchmark
# Run progress: 50,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 271,938 us/op
# Warmup Iteration 2: 258,261 us/op
# Warmup Iteration 3: 257,976 us/op
# Warmup Iteration 4: 256,103 us/op
# Warmup Iteration 5: 255,863 us/op
Iteration 1: 266,376 us/op
Iteration 2: 258,158 us/op
Iteration 3: 278,038 us/op
Iteration 4: 271,354 us/op
Iteration 5: 256,021 us/op
Iteration 6: 254,590 us/op
Iteration 7: 254,944 us/op
Iteration 8: 255,525 us/op
Iteration 9: 256,339 us/op
Iteration 10: 257,311 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithoutBiasedLockingBenchmark.forEachStreamBenchmark":
260,866 ±(99.9%) 12,366 us/op [Average]
(min, avg, max) = (254,590, 260,866, 278,038), stdev = 8,180
CI (99.9%): [248,499, 273,232] (assumes normal distribution)
# Run complete. Total time: 00:01:00
Benchmark Mode Cnt Score Error Units
StreamWithoutBiasedLockingBenchmark.forEachParallelStreamBenchmark avgt 10 703,067 ± 28,058 us/op
StreamWithoutBiasedLockingBenchmark.forEachStreamBenchmark avgt 10 260,866 ± 12,366 us/op
Ожидаемо просела производительность обычного ArrayList.forEach()
. При этом по прогревочным итерациям в предыдущем бенчмарке заметно ускорение, начиная с третьей итерации, — это не случайность. Дело в том, что по умолчанию biased locking включается спустя 4000 мс с момента запуска виртуальной машины. Это значение можно потюнить и посмотреть, что получится:
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0, jvmArgsAppend = "-XX:BiasedLockingStartupDelay=6000")
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.MICROSECONDS)
@BenchmarkMode(Mode.AverageTime)
public class StreamWithNewBiasedLockingStartupDelayBenchmark {
static int N = 1000;
static List<Integer> values;
static {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@State(value = Scope.Benchmark)
public static class PrintStreamHolder {
PrintStream ps;
@Setup(value = Level.Iteration)
public void setup() {
ps = new PrintStream(new NullOutputStream());
}
}
@Benchmark
public void forEachStreamBenchmark(PrintStreamHolder psh) {
forEachStream(values, psh.ps);
}
@Benchmark
public void forEachParallelStreamBenchmark(PrintStreamHolder psh) {
forEachParallelStream(values, psh.ps);
}
public void forEachStream(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
public void forEachParallelStream(List<Integer> values, PrintStream ps) {
values.parallelStream().forEach(ps::println);
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: -XX:BiasedLockingStartupDelay=6000
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithNewBiasedLockingStartupDelayBenchmark.forEachParallelStreamBenchmark
# Run progress: 0,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 954,533 us/op
# Warmup Iteration 2: 866,854 us/op
# Warmup Iteration 3: 907,109 us/op
# Warmup Iteration 4: 914,717 us/op
# Warmup Iteration 5: 924,102 us/op
Iteration 1: 912,619 us/op
Iteration 2: 947,812 us/op
Iteration 3: 925,730 us/op
Iteration 4: 933,807 us/op
Iteration 5: 935,927 us/op
Iteration 6: 852,369 us/op
Iteration 7: 882,498 us/op
Iteration 8: 852,625 us/op
Iteration 9: 898,787 us/op
Iteration 10: 1150,831 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithNewBiasedLockingStartupDelayBenchmark.forEachParallelStreamBenchmark":
929,301 ±(99.9%) 128,179 us/op [Average]
(min, avg, max) = (852,369, 929,301, 1150,831), stdev = 84,783
CI (99.9%): [801,121, 1057,480] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: -XX:BiasedLockingStartupDelay=6000
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithNewBiasedLockingStartupDelayBenchmark.forEachStreamBenchmark
# Run progress: 50,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 346,853 us/op
# Warmup Iteration 2: 280,643 us/op
# Warmup Iteration 3: 264,425 us/op
# Warmup Iteration 4: 169,200 us/op
# Warmup Iteration 5: 167,981 us/op
Iteration 1: 171,230 us/op
Iteration 2: 169,891 us/op
Iteration 3: 169,124 us/op
Iteration 4: 167,938 us/op
Iteration 5: 167,471 us/op
Iteration 6: 176,187 us/op
Iteration 7: 171,791 us/op
Iteration 8: 170,127 us/op
Iteration 9: 169,563 us/op
Iteration 10: 169,062 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.StreamWithNewBiasedLockingStartupDelayBenchmark.forEachStreamBenchmark":
170,238 ±(99.9%) 3,736 us/op [Average]
(min, avg, max) = (167,471, 170,238, 176,187), stdev = 2,471
CI (99.9%): [166,503, 173,974] (assumes normal distribution)
# Run complete. Total time: 00:01:00
Benchmark Mode Cnt Score Error Units
StreamWithNewBiasedLockingStartupDelayBenchmark.forEachParallelStreamBenchmark avgt 10 929,301 ± 128,179 us/op
StreamWithNewBiasedLockingStartupDelayBenchmark.forEachStreamBenchmark avgt 10 170,238 ± 3,736 us/op
Как и ожидалось, эффект от biased locking наступил только спустя 6 секунд с начала выполнения бенчмарка — это видно по разнице во времени выполнения третьей и четвёртой прогревочной итерации.
List.forEach() vs List.stream().forEach()
Теперь пришло время разобраться, что быстрее: List.forEach()
или List.stream().forEach()
. Правильный ответ «зависит от». На результат влияет размер списка, тип списка, возможность применения инлайнинга и других оптимизаций JIT-компилятором. Возможно, нам удастся выявить общее правило. Ниже результат для ArrayList
:
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0)
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.MICROSECONDS)
@BenchmarkMode(Mode.AverageTime)
@State(Scope.Benchmark)
public class ArrayListVsStreamBenchmark {
@Param(value = {"1", "10", "100", "1000", "10000"})
public int N;
private List<Integer> values;
@Setup
public void setup() {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@State(value = Scope.Benchmark)
public static class PrintStreamHolder {
PrintStream ps;
@Setup(value = Level.Iteration)
public void setup() {
ps = new PrintStream(new NullOutputStream());
}
}
@Benchmark
public void forEachListBenchmark(PrintStreamHolder psh) {
forEachList(values, psh.ps);
}
@Benchmark
public void forEachStreamBenchmark(PrintStreamHolder psh) {
forEachStream(values, psh.ps);
}
public void forEachList(List<Integer> values, PrintStream ps) {
values.forEach(ps::println);
}
public void forEachStream(List<Integer> values, PrintStream ps) {
values.stream().forEach(ps::println);
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark
# Parameters: (N = 1)
# Run progress: 0,00% complete, ETA 00:05:00
# Fork: 1 of 1
# Warmup Iteration 1: 0,288 us/op
# Warmup Iteration 2: 0,277 us/op
# Warmup Iteration 3: 0,178 us/op
# Warmup Iteration 4: 0,177 us/op
# Warmup Iteration 5: 0,178 us/op
Iteration 1: 0,177 us/op
Iteration 2: 0,178 us/op
Iteration 3: 0,178 us/op
Iteration 4: 0,178 us/op
Iteration 5: 0,178 us/op
Iteration 6: 0,178 us/op
Iteration 7: 0,178 us/op
Iteration 8: 0,179 us/op
Iteration 9: 0,178 us/op
Iteration 10: 0,180 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark":
0,178 ±(99.9%) 0,001 us/op [Average]
(min, avg, max) = (0,177, 0,178, 0,180), stdev = 0,001
CI (99.9%): [0,177, 0,179] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark
# Parameters: (N = 10)
# Run progress: 10,00% complete, ETA 00:04:33
# Fork: 1 of 1
# Warmup Iteration 1: 2,933 us/op
# Warmup Iteration 2: 2,839 us/op
# Warmup Iteration 3: 1,661 us/op
# Warmup Iteration 4: 1,675 us/op
# Warmup Iteration 5: 1,674 us/op
Iteration 1: 1,682 us/op
Iteration 2: 1,653 us/op
Iteration 3: 1,658 us/op
Iteration 4: 1,656 us/op
Iteration 5: 1,659 us/op
Iteration 6: 1,655 us/op
Iteration 7: 1,656 us/op
Iteration 8: 1,657 us/op
Iteration 9: 1,661 us/op
Iteration 10: 1,660 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark":
1,660 ±(99.9%) 0,013 us/op [Average]
(min, avg, max) = (1,653, 1,660, 1,682), stdev = 0,008
CI (99.9%): [1,647, 1,672] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark
# Parameters: (N = 100)
# Run progress: 20,00% complete, ETA 00:04:02
# Fork: 1 of 1
# Warmup Iteration 1: 27,633 us/op
# Warmup Iteration 2: 27,184 us/op
# Warmup Iteration 3: 15,046 us/op
# Warmup Iteration 4: 15,064 us/op
# Warmup Iteration 5: 15,060 us/op
Iteration 1: 15,039 us/op
Iteration 2: 15,057 us/op
Iteration 3: 15,065 us/op
Iteration 4: 15,062 us/op
Iteration 5: 15,086 us/op
Iteration 6: 15,060 us/op
Iteration 7: 15,110 us/op
Iteration 8: 15,070 us/op
Iteration 9: 15,111 us/op
Iteration 10: 15,079 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark":
15,074 ±(99.9%) 0,035 us/op [Average]
(min, avg, max) = (15,039, 15,074, 15,111), stdev = 0,023
CI (99.9%): [15,039, 15,109] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark
# Parameters: (N = 1000)
# Run progress: 30,00% complete, ETA 00:03:32
# Fork: 1 of 1
# Warmup Iteration 1: 291,532 us/op
# Warmup Iteration 2: 267,136 us/op
# Warmup Iteration 3: 170,432 us/op
# Warmup Iteration 4: 170,388 us/op
# Warmup Iteration 5: 169,797 us/op
Iteration 1: 170,036 us/op
Iteration 2: 176,614 us/op
Iteration 3: 176,396 us/op
Iteration 4: 175,895 us/op
Iteration 5: 176,984 us/op
Iteration 6: 172,085 us/op
Iteration 7: 170,193 us/op
Iteration 8: 171,333 us/op
Iteration 9: 170,293 us/op
Iteration 10: 171,006 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark":
173,084 ±(99.9%) 4,518 us/op [Average]
(min, avg, max) = (170,036, 173,084, 176,984), stdev = 2,988
CI (99.9%): [168,566, 177,601] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark
# Parameters: (N = 10000)
# Run progress: 40,00% complete, ETA 00:03:01
# Fork: 1 of 1
# Warmup Iteration 1: 2890,241 us/op
# Warmup Iteration 2: 2784,740 us/op
# Warmup Iteration 3: 1725,390 us/op
# Warmup Iteration 4: 1726,138 us/op
# Warmup Iteration 5: 1733,212 us/op
Iteration 1: 1726,084 us/op
Iteration 2: 1712,973 us/op
Iteration 3: 1715,916 us/op
Iteration 4: 1750,530 us/op
Iteration 5: 1721,900 us/op
Iteration 6: 1711,158 us/op
Iteration 7: 1709,659 us/op
Iteration 8: 1726,751 us/op
Iteration 9: 1737,237 us/op
Iteration 10: 1734,220 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachListBenchmark":
1724,643 ±(99.9%) 19,861 us/op [Average]
(min, avg, max) = (1709,659, 1724,643, 1750,530), stdev = 13,137
CI (99.9%): [1704,782, 1744,504] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark
# Parameters: (N = 1)
# Run progress: 50,00% complete, ETA 00:02:31
# Fork: 1 of 1
# Warmup Iteration 1: 0,301 us/op
# Warmup Iteration 2: 0,289 us/op
# Warmup Iteration 3: 0,181 us/op
# Warmup Iteration 4: 0,180 us/op
# Warmup Iteration 5: 0,181 us/op
Iteration 1: 0,179 us/op
Iteration 2: 0,178 us/op
Iteration 3: 0,179 us/op
Iteration 4: 0,180 us/op
Iteration 5: 0,179 us/op
Iteration 6: 0,179 us/op
Iteration 7: 0,180 us/op
Iteration 8: 0,179 us/op
Iteration 9: 0,180 us/op
Iteration 10: 0,180 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark":
0,179 ±(99.9%) 0,001 us/op [Average]
(min, avg, max) = (0,178, 0,179, 0,180), stdev = 0,001
CI (99.9%): [0,178, 0,180] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark
# Parameters: (N = 10)
# Run progress: 60,00% complete, ETA 00:02:01
# Fork: 1 of 1
# Warmup Iteration 1: 2,660 us/op
# Warmup Iteration 2: 2,551 us/op
# Warmup Iteration 3: 1,558 us/op
# Warmup Iteration 4: 1,563 us/op
# Warmup Iteration 5: 1,563 us/op
Iteration 1: 1,557 us/op
Iteration 2: 1,553 us/op
Iteration 3: 1,567 us/op
Iteration 4: 1,555 us/op
Iteration 5: 1,569 us/op
Iteration 6: 1,570 us/op
Iteration 7: 1,562 us/op
Iteration 8: 1,561 us/op
Iteration 9: 1,564 us/op
Iteration 10: 1,580 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark":
1,564 ±(99.9%) 0,012 us/op [Average]
(min, avg, max) = (1,553, 1,564, 1,580), stdev = 0,008
CI (99.9%): [1,552, 1,576] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark
# Parameters: (N = 100)
# Run progress: 70,00% complete, ETA 00:01:30
# Fork: 1 of 1
# Warmup Iteration 1: 27,754 us/op
# Warmup Iteration 2: 26,859 us/op
# Warmup Iteration 3: 16,456 us/op
# Warmup Iteration 4: 16,548 us/op
# Warmup Iteration 5: 16,432 us/op
Iteration 1: 16,399 us/op
Iteration 2: 16,480 us/op
Iteration 3: 16,517 us/op
Iteration 4: 16,458 us/op
Iteration 5: 16,395 us/op
Iteration 6: 16,471 us/op
Iteration 7: 16,595 us/op
Iteration 8: 16,585 us/op
Iteration 9: 16,460 us/op
Iteration 10: 16,435 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark":
16,479 ±(99.9%) 0,104 us/op [Average]
(min, avg, max) = (16,395, 16,479, 16,595), stdev = 0,069
CI (99.9%): [16,376, 16,583] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark
# Parameters: (N = 1000)
# Run progress: 80,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 291,695 us/op
# Warmup Iteration 2: 282,896 us/op
# Warmup Iteration 3: 185,443 us/op
# Warmup Iteration 4: 187,851 us/op
# Warmup Iteration 5: 184,393 us/op
Iteration 1: 184,584 us/op
Iteration 2: 185,349 us/op
Iteration 3: 184,803 us/op
Iteration 4: 184,394 us/op
Iteration 5: 185,371 us/op
Iteration 6: 186,735 us/op
Iteration 7: 185,945 us/op
Iteration 8: 188,592 us/op
Iteration 9: 186,581 us/op
Iteration 10: 187,908 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark":
186,026 ±(99.9%) 2,142 us/op [Average]
(min, avg, max) = (184,394, 186,026, 188,592), stdev = 1,417
CI (99.9%): [183,884, 188,168] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark
# Parameters: (N = 10000)
# Run progress: 90,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 2896,624 us/op
# Warmup Iteration 2: 2816,471 us/op
# Warmup Iteration 3: 1732,597 us/op
# Warmup Iteration 4: 1798,371 us/op
# Warmup Iteration 5: 1758,489 us/op
Iteration 1: 1615,213 us/op
Iteration 2: 1518,388 us/op
Iteration 3: 1513,955 us/op
Iteration 4: 1520,570 us/op
Iteration 5: 1525,072 us/op
Iteration 6: 1527,055 us/op
Iteration 7: 1547,707 us/op
Iteration 8: 1532,163 us/op
Iteration 9: 1519,474 us/op
Iteration 10: 1529,969 us/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.ArrayListVsStreamBenchmark.forEachStreamBenchmark":
1534,957 ±(99.9%) 44,959 us/op [Average]
(min, avg, max) = (1513,955, 1534,957, 1615,213), stdev = 29,737
CI (99.9%): [1489,998, 1579,915] (assumes normal distribution)
# Run complete. Total time: 00:05:03
Benchmark (N) Mode Cnt Score Error Units
ArrayListVsStreamBenchmark.forEachListBenchmark 1 avgt 10 0,178 ± 0,001 us/op
ArrayListVsStreamBenchmark.forEachListBenchmark 10 avgt 10 1,660 ± 0,013 us/op
ArrayListVsStreamBenchmark.forEachListBenchmark 100 avgt 10 15,074 ± 0,035 us/op
ArrayListVsStreamBenchmark.forEachListBenchmark 1000 avgt 10 173,084 ± 4,518 us/op
ArrayListVsStreamBenchmark.forEachListBenchmark 10000 avgt 10 1724,643 ± 19,861 us/op
ArrayListVsStreamBenchmark.forEachStreamBenchmark 1 avgt 10 0,179 ± 0,001 us/op
ArrayListVsStreamBenchmark.forEachStreamBenchmark 10 avgt 10 1,564 ± 0,012 us/op
ArrayListVsStreamBenchmark.forEachStreamBenchmark 100 avgt 10 16,479 ± 0,104 us/op
ArrayListVsStreamBenchmark.forEachStreamBenchmark 1000 avgt 10 186,026 ± 2,142 us/op
ArrayListVsStreamBenchmark.forEachStreamBenchmark 10000 avgt 10 1534,957 ± 44,959 us/op
В действительности, накладные расходы на итерирование намного меньше, чем накладные расходы на вызов метода PrintStream.println()
. Чтобы убедиться в этом, достаточно заменить вызов метода PrintStrim.println()
на вызов Blackhole.consume()
(последний гарантирует, что JIT-компилятор не выпилит ставшую бесполезной часть кода и итерирование отработает). Обратите внимание, что результат уже не в микросекундах, а в наносекундах!
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0)
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.NANOSECONDS)
@BenchmarkMode(Mode.AverageTime)
@State(Scope.Benchmark)
public class BlackholeConsumingBenchmark {
@Param(value = {"1", "10", "100", "1000", "10000"})
public int N;
private List<Integer> values;
@Setup
public void setup() {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@Benchmark
public void forEachListBenchmark(Blackhole bh) {
forEachList(values, bh);
}
@Benchmark
public void forEachStreamBenchmark(Blackhole bh) {
forEachStream(values, bh);
}
public void forEachList(List<Integer> values, Blackhole bh) {
values.forEach(bh::consume);
}
public void forEachStream(List<Integer> values, Blackhole bh) {
values.stream().forEach(bh::consume);
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 1)
# Run progress: 0,00% complete, ETA 00:05:00
# Fork: 1 of 1
# Warmup Iteration 1: 6,866 ns/op
# Warmup Iteration 2: 6,865 ns/op
# Warmup Iteration 3: 6,528 ns/op
# Warmup Iteration 4: 6,524 ns/op
# Warmup Iteration 5: 6,521 ns/op
Iteration 1: 6,519 ns/op
Iteration 2: 6,542 ns/op
Iteration 3: 6,608 ns/op
Iteration 4: 6,590 ns/op
Iteration 5: 6,678 ns/op
Iteration 6: 6,658 ns/op
Iteration 7: 6,756 ns/op
Iteration 8: 6,933 ns/op
Iteration 9: 6,939 ns/op
Iteration 10: 6,811 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark":
6,703 ±(99.9%) 0,230 ns/op [Average]
(min, avg, max) = (6,519, 6,703, 6,939), stdev = 0,152
CI (99.9%): [6,474, 6,933] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 10)
# Run progress: 10,00% complete, ETA 00:04:32
# Fork: 1 of 1
# Warmup Iteration 1: 51,655 ns/op
# Warmup Iteration 2: 50,507 ns/op
# Warmup Iteration 3: 50,309 ns/op
# Warmup Iteration 4: 50,886 ns/op
# Warmup Iteration 5: 50,068 ns/op
Iteration 1: 51,218 ns/op
Iteration 2: 50,108 ns/op
Iteration 3: 52,343 ns/op
Iteration 4: 50,745 ns/op
Iteration 5: 51,461 ns/op
Iteration 6: 50,366 ns/op
Iteration 7: 49,976 ns/op
Iteration 8: 50,623 ns/op
Iteration 9: 50,223 ns/op
Iteration 10: 50,125 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark":
50,719 ±(99.9%) 1,138 ns/op [Average]
(min, avg, max) = (49,976, 50,719, 52,343), stdev = 0,753
CI (99.9%): [49,581, 51,857] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 100)
# Run progress: 20,00% complete, ETA 00:04:02
# Fork: 1 of 1
# Warmup Iteration 1: 574,874 ns/op
# Warmup Iteration 2: 557,543 ns/op
# Warmup Iteration 3: 557,260 ns/op
# Warmup Iteration 4: 556,273 ns/op
# Warmup Iteration 5: 556,025 ns/op
Iteration 1: 555,532 ns/op
Iteration 2: 558,421 ns/op
Iteration 3: 564,582 ns/op
Iteration 4: 573,368 ns/op
Iteration 5: 576,355 ns/op
Iteration 6: 562,087 ns/op
Iteration 7: 565,229 ns/op
Iteration 8: 574,557 ns/op
Iteration 9: 561,430 ns/op
Iteration 10: 574,486 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark":
566,605 ±(99.9%) 11,369 ns/op [Average]
(min, avg, max) = (555,532, 566,605, 576,355), stdev = 7,520
CI (99.9%): [555,236, 577,974] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 1000)
# Run progress: 30,00% complete, ETA 00:03:32
# Fork: 1 of 1
# Warmup Iteration 1: 4782,869 ns/op
# Warmup Iteration 2: 4920,389 ns/op
# Warmup Iteration 3: 4845,857 ns/op
# Warmup Iteration 4: 4847,470 ns/op
# Warmup Iteration 5: 4857,726 ns/op
Iteration 1: 4850,519 ns/op
Iteration 2: 4852,075 ns/op
Iteration 3: 4907,015 ns/op
Iteration 4: 4859,020 ns/op
Iteration 5: 4879,201 ns/op
Iteration 6: 4832,822 ns/op
Iteration 7: 4831,532 ns/op
Iteration 8: 4829,599 ns/op
Iteration 9: 4878,201 ns/op
Iteration 10: 4826,464 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark":
4854,645 ±(99.9%) 40,238 ns/op [Average]
(min, avg, max) = (4826,464, 4854,645, 4907,015), stdev = 26,615
CI (99.9%): [4814,407, 4894,883] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 10000)
# Run progress: 40,00% complete, ETA 00:03:01
# Fork: 1 of 1
# Warmup Iteration 1: 42925,340 ns/op
# Warmup Iteration 2: 47991,419 ns/op
# Warmup Iteration 3: 50854,318 ns/op
# Warmup Iteration 4: 51251,774 ns/op
# Warmup Iteration 5: 51756,902 ns/op
Iteration 1: 51102,960 ns/op
Iteration 2: 51420,802 ns/op
Iteration 3: 51744,142 ns/op
Iteration 4: 50985,401 ns/op
Iteration 5: 51125,197 ns/op
Iteration 6: 51223,229 ns/op
Iteration 7: 51424,190 ns/op
Iteration 8: 51457,326 ns/op
Iteration 9: 51410,258 ns/op
Iteration 10: 51419,014 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachListBenchmark":
51331,252 ±(99.9%) 335,358 ns/op [Average]
(min, avg, max) = (50985,401, 51331,252, 51744,142), stdev = 221,819
CI (99.9%): [50995,894, 51666,610] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 1)
# Run progress: 50,00% complete, ETA 00:02:31
# Fork: 1 of 1
# Warmup Iteration 1: 25,963 ns/op
# Warmup Iteration 2: 20,840 ns/op
# Warmup Iteration 3: 18,882 ns/op
# Warmup Iteration 4: 19,081 ns/op
# Warmup Iteration 5: 19,513 ns/op
Iteration 1: 19,411 ns/op
Iteration 2: 18,856 ns/op
Iteration 3: 19,049 ns/op
Iteration 4: 18,891 ns/op
Iteration 5: 19,136 ns/op
Iteration 6: 20,116 ns/op
Iteration 7: 19,490 ns/op
Iteration 8: 19,251 ns/op
Iteration 9: 19,767 ns/op
Iteration 10: 19,607 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark":
19,357 ±(99.9%) 0,607 ns/op [Average]
(min, avg, max) = (18,856, 19,357, 20,116), stdev = 0,401
CI (99.9%): [18,751, 19,964] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 10)
# Run progress: 60,00% complete, ETA 00:02:01
# Fork: 1 of 1
# Warmup Iteration 1: 59,828 ns/op
# Warmup Iteration 2: 52,901 ns/op
# Warmup Iteration 3: 44,941 ns/op
# Warmup Iteration 4: 44,833 ns/op
# Warmup Iteration 5: 44,962 ns/op
Iteration 1: 46,032 ns/op
Iteration 2: 45,802 ns/op
Iteration 3: 45,018 ns/op
Iteration 4: 45,704 ns/op
Iteration 5: 45,788 ns/op
Iteration 6: 46,674 ns/op
Iteration 7: 46,588 ns/op
Iteration 8: 48,083 ns/op
Iteration 9: 46,862 ns/op
Iteration 10: 47,087 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark":
46,364 ±(99.9%) 1,321 ns/op [Average]
(min, avg, max) = (45,018, 46,364, 48,083), stdev = 0,874
CI (99.9%): [45,042, 47,685] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 100)
# Run progress: 70,00% complete, ETA 00:01:31
# Fork: 1 of 1
# Warmup Iteration 1: 382,038 ns/op
# Warmup Iteration 2: 347,846 ns/op
# Warmup Iteration 3: 337,712 ns/op
# Warmup Iteration 4: 335,078 ns/op
# Warmup Iteration 5: 344,895 ns/op
Iteration 1: 329,577 ns/op
Iteration 2: 328,436 ns/op
Iteration 3: 329,517 ns/op
Iteration 4: 330,736 ns/op
Iteration 5: 335,464 ns/op
Iteration 6: 338,727 ns/op
Iteration 7: 330,996 ns/op
Iteration 8: 330,809 ns/op
Iteration 9: 329,599 ns/op
Iteration 10: 330,580 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark":
331,444 ±(99.9%) 4,800 ns/op [Average]
(min, avg, max) = (328,436, 331,444, 338,727), stdev = 3,175
CI (99.9%): [326,645, 336,244] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 1000)
# Run progress: 80,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 3734,819 ns/op
# Warmup Iteration 2: 3534,547 ns/op
# Warmup Iteration 3: 3201,812 ns/op
# Warmup Iteration 4: 3151,474 ns/op
# Warmup Iteration 5: 3136,897 ns/op
Iteration 1: 3138,505 ns/op
Iteration 2: 3137,993 ns/op
Iteration 3: 3141,723 ns/op
Iteration 4: 3225,711 ns/op
Iteration 5: 3127,945 ns/op
Iteration 6: 3129,312 ns/op
Iteration 7: 3141,355 ns/op
Iteration 8: 3137,377 ns/op
Iteration 9: 3149,419 ns/op
Iteration 10: 3243,662 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark":
3157,300 ±(99.9%) 62,671 ns/op [Average]
(min, avg, max) = (3127,945, 3157,300, 3243,662), stdev = 41,453
CI (99.9%): [3094,629, 3219,972] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 10000)
# Run progress: 90,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 45988,758 ns/op
# Warmup Iteration 2: 45331,295 ns/op
# Warmup Iteration 3: 38213,299 ns/op
# Warmup Iteration 4: 31233,461 ns/op
# Warmup Iteration 5: 31321,451 ns/op
Iteration 1: 31470,793 ns/op
Iteration 2: 32267,081 ns/op
Iteration 3: 31619,772 ns/op
Iteration 4: 32155,094 ns/op
Iteration 5: 31304,547 ns/op
Iteration 6: 31484,244 ns/op
Iteration 7: 31709,801 ns/op
Iteration 8: 31297,118 ns/op
Iteration 9: 31305,782 ns/op
Iteration 10: 31320,821 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.BlackholeConsumingBenchmark.forEachStreamBenchmark":
31593,505 ±(99.9%) 537,786 ns/op [Average]
(min, avg, max) = (31297,118, 31593,505, 32267,081), stdev = 355,712
CI (99.9%): [31055,719, 32131,292] (assumes normal distribution)
# Run complete. Total time: 00:05:03
Benchmark (N) Mode Cnt Score Error Units
BlackholeConsumingBenchmark.forEachListBenchmark 1 avgt 10 6,703 ± 0,230 ns/op
BlackholeConsumingBenchmark.forEachListBenchmark 10 avgt 10 50,719 ± 1,138 ns/op
BlackholeConsumingBenchmark.forEachListBenchmark 100 avgt 10 566,605 ± 11,369 ns/op
BlackholeConsumingBenchmark.forEachListBenchmark 1000 avgt 10 4854,645 ± 40,238 ns/op
BlackholeConsumingBenchmark.forEachListBenchmark 10000 avgt 10 51331,252 ± 335,358 ns/op
BlackholeConsumingBenchmark.forEachStreamBenchmark 1 avgt 10 19,357 ± 0,607 ns/op
BlackholeConsumingBenchmark.forEachStreamBenchmark 10 avgt 10 46,364 ± 1,321 ns/op
BlackholeConsumingBenchmark.forEachStreamBenchmark 100 avgt 10 331,444 ± 4,800 ns/op
BlackholeConsumingBenchmark.forEachStreamBenchmark 1000 avgt 10 3157,300 ± 62,671 ns/op
BlackholeConsumingBenchmark.forEachStreamBenchmark 10000 avgt 10 31593,505 ± 537,786 ns/op
И становится интереснее: разница между ArrayList.forEach()
и ArrayList.stream().forEach()
получилась достаточно большой на длинных списках. Более того, прогрев никак не ускоряет ArrayList.forEach()
, тогда как ArrayList.stream().forEach()
заметно ускоряется.
Дело в том, что накладные расходы на создание Stream
оказывают влияние лишь на списках малого размера. В дальнейшем всё сводится к непосредственному итерированию.
Так выглядит ArrayList.forEach()
:
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
@SuppressWarnings("unchecked")
final E[] elementData = (E[]) this.elementData;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
action.accept(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
Так выглядит код ArrayList.ArrayListSpliterator.forEachRemaining()
:
public void forEachRemaining(Consumer<? super E> action) {
int i, hi, mc; // hoist accesses and checks from loop
ArrayList<E> lst; Object[] a;
if (action == null)
throw new NullPointerException();
if ((lst = list) != null && (a = lst.elementData) != null) {
if ((hi = fence) < 0) {
mc = lst.modCount;
hi = lst.size;
}
else
mc = expectedModCount;
if ((i = index) >= 0 && (index = hi) <= a.length) {
for (; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) a[i];
action.accept(e);
}
if (lst.modCount == mc)
return;
}
}
throw new ConcurrentModificationException();
}
Как видим, разница в коде не существенная (циклы for внутри методов): дальше в дело вступает JIT-компилятор. Андрей apangin помог разобраться в чём тут дело: Blackhole.consume()
не инлайнится и JIT-компилятор не может как следует оптимизировать код: в итоге остаётся и чтение поля modCount
, и проверка границ массива.
Действительно, попробуем заменить Blackhole.consume()
на свой самопальный метод:
package ru.gnkoshelev.jbreak2018.perf_tests.for_each;
@Fork(value = 1, warmups = 0)
@Warmup(iterations = 5, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 2_000, timeUnit = TimeUnit.MILLISECONDS)
@OutputTimeUnit(value = TimeUnit.NANOSECONDS)
@BenchmarkMode(Mode.AverageTime)
@State(Scope.Benchmark)
public class TrickyConsumingBenchmark {
@Param(value = {"100", "10000"})
public int N;
private List<Integer> values;
@Setup
public void setup() {
Random rand = new Random(12345);
int size = N;
values = new ArrayList<>();
for (int i = 0; i < size; i++) {
values.add(rand.nextInt());
}
}
@Benchmark
public void forEachListBenchmark() {
forEachList(values);
}
@Benchmark
public void forEachStreamBenchmark() {
forEachStream(values);
}
public void forEachList(List<Integer> values) {
values.forEach(TrickyConsumer::consume);
}
public void forEachStream(List<Integer> values) {
values.stream().forEach(TrickyConsumer::consume);
}
public static class TrickyConsumer {
public static Integer value;
public static void consume(Integer value) {
if (! (value % 100 == 0)) {
TrickyConsumer.value = value;
}
}
}
}
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 100)
# Run progress: 0,00% complete, ETA 00:02:00
# Fork: 1 of 1
# Warmup Iteration 1: 205,489 ns/op
# Warmup Iteration 2: 205,514 ns/op
# Warmup Iteration 3: 216,056 ns/op
# Warmup Iteration 4: 208,956 ns/op
# Warmup Iteration 5: 204,900 ns/op
Iteration 1: 205,535 ns/op
Iteration 2: 210,834 ns/op
Iteration 3: 206,050 ns/op
Iteration 4: 205,962 ns/op
Iteration 5: 205,285 ns/op
Iteration 6: 205,581 ns/op
Iteration 7: 204,991 ns/op
Iteration 8: 209,290 ns/op
Iteration 9: 203,927 ns/op
Iteration 10: 204,977 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachListBenchmark":
206,243 ±(99.9%) 3,222 ns/op [Average]
(min, avg, max) = (203,927, 206,243, 210,834), stdev = 2,131
CI (99.9%): [203,021, 209,465] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachListBenchmark
# Parameters: (N = 10000)
# Run progress: 25,00% complete, ETA 00:01:30
# Fork: 1 of 1
# Warmup Iteration 1: 22733,300 ns/op
# Warmup Iteration 2: 22197,064 ns/op
# Warmup Iteration 3: 21640,616 ns/op
# Warmup Iteration 4: 21411,160 ns/op
# Warmup Iteration 5: 21702,499 ns/op
Iteration 1: 21921,831 ns/op
Iteration 2: 21970,321 ns/op
Iteration 3: 21409,419 ns/op
Iteration 4: 21171,131 ns/op
Iteration 5: 22011,961 ns/op
Iteration 6: 22063,926 ns/op
Iteration 7: 21825,015 ns/op
Iteration 8: 21820,783 ns/op
Iteration 9: 22089,657 ns/op
Iteration 10: 21626,934 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachListBenchmark":
21791,098 ±(99.9%) 456,511 ns/op [Average]
(min, avg, max) = (21171,131, 21791,098, 22089,657), stdev = 301,954
CI (99.9%): [21334,587, 22247,609] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 100)
# Run progress: 50,00% complete, ETA 00:01:00
# Fork: 1 of 1
# Warmup Iteration 1: 250,480 ns/op
# Warmup Iteration 2: 247,070 ns/op
# Warmup Iteration 3: 269,745 ns/op
# Warmup Iteration 4: 269,914 ns/op
# Warmup Iteration 5: 272,912 ns/op
Iteration 1: 269,779 ns/op
Iteration 2: 270,502 ns/op
Iteration 3: 269,128 ns/op
Iteration 4: 273,862 ns/op
Iteration 5: 275,447 ns/op
Iteration 6: 272,090 ns/op
Iteration 7: 271,189 ns/op
Iteration 8: 271,714 ns/op
Iteration 9: 269,121 ns/op
Iteration 10: 269,913 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachStreamBenchmark":
271,275 ±(99.9%) 3,144 ns/op [Average]
(min, avg, max) = (269,121, 271,275, 275,447), stdev = 2,079
CI (99.9%): [268,131, 274,418] (assumes normal distribution)
# JMH version: 1.20
# VM version: JDK 1.8.0_161, VM 25.161-b12
# VM invoker: C:Program FilesJavajre1.8.0_161binjava.exe
# VM options: <none>
# Warmup: 5 iterations, 2000 ms each
# Measurement: 10 iterations, 2000 ms each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachStreamBenchmark
# Parameters: (N = 10000)
# Run progress: 75,00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration 1: 22612,079 ns/op
# Warmup Iteration 2: 24943,260 ns/op
# Warmup Iteration 3: 23366,453 ns/op
# Warmup Iteration 4: 23445,251 ns/op
# Warmup Iteration 5: 23732,635 ns/op
Iteration 1: 23575,011 ns/op
Iteration 2: 23478,581 ns/op
Iteration 3: 23663,154 ns/op
Iteration 4: 23067,535 ns/op
Iteration 5: 23489,020 ns/op
Iteration 6: 23461,241 ns/op
Iteration 7: 23510,542 ns/op
Iteration 8: 23504,541 ns/op
Iteration 9: 24036,074 ns/op
Iteration 10: 24081,512 ns/op
Result "ru.gnkoshelev.jbreak2018.perf_tests.for_each.TrickyConsumingBenchmark.forEachStreamBenchmark":
23586,721 ±(99.9%) 442,736 ns/op [Average]
(min, avg, max) = (23067,535, 23586,721, 24081,512), stdev = 292,843
CI (99.9%): [23143,985, 24029,458] (assumes normal distribution)
# Run complete. Total time: 00:02:01
Benchmark (N) Mode Cnt Score Error Units
TrickyConsumingBenchmark.forEachListBenchmark 100 avgt 10 206,243 ± 3,222 ns/op
TrickyConsumingBenchmark.forEachListBenchmark 10000 avgt 10 21791,098 ± 456,511 ns/op
TrickyConsumingBenchmark.forEachStreamBenchmark 100 avgt 10 271,275 ± 3,144 ns/op
TrickyConsumingBenchmark.forEachStreamBenchmark 10000 avgt 10 23586,721 ± 442,736 ns/op
Всё вернулось на круги своя, а как уж тут отработал JIT — совсем другая история.
Выводы
1. Какой же в итоге правильный ответ? методы 1 и 2 в задаче дают незначительно отличающиеся результаты, а метод 3 значительно уступает в производительности.
2. В качестве правильно ответа принимались альтернативные варианты, что 1 быстрее 2 и 2 быстрее 1, если это было верно аргументировано.
3. Личный вывод: кроличья нора оказывается всегда глубже, чем думаешь.
Код бенчмарков можно взять на github: jbreak2018-forEach-perf-tests.
Статистика
Из 32 сданных вариантов было 8 правильных и 5 частично правильных. Ещё 7 человек попали в PrintStream
-ловушку, посчитав параллельный Stream
самым быстрым. Никто не поверил в последовательные стримы и не выбрал вариант 2 в качестве самого быстрого.
P.S.
Следующую часть постараюсь подготовить на следующих выходных.
Автор: Григорий Кошелев