我想要对简单for循环和等效的流实现进行性能测量和比较。我相信流会比等效的非流代码稍微慢一些,但我想确保我正在测量正确的东西。
我在这里包含了整个jmh类。
import java.util.ArrayList;
import java.util.List;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
@State(Scope.Benchmark)
public class MyBenchmark {
List<String> shortLengthListConstantSize = null;
List<String> mediumLengthListConstantSize = null;
List<String> longerLengthListConstantSize = null;
List<String> longLengthListConstantSize = null;
@Setup
public void setup() {
shortLengthListConstantSize = populateList(2);
mediumLengthListConstantSize = populateList(12);
longerLengthListConstantSize = populateList(300);
longLengthListConstantSize = populateList(300000);
}
private List<String> populateList(int size) {
List<String> list = new ArrayList<>();
for (int ctr = 0; ctr < size; ++ ctr) {
list.add("xxx");
}
return list;
}
@Benchmark
public long shortLengthConstantSizeFor() {
long count = 0;
for (String val : shortLengthListConstantSize) {
if (val.length() == 3) { ++ count; }
}
return count;
}
@Benchmark
public long shortLengthConstantSizeForEach() {
IntHolder intHolder = new IntHolder();
shortLengthListConstantSize.forEach(s -> { if (s.length() == 3) ++ intHolder.value; } );
return intHolder.value;
}
@Benchmark
public long shortLengthConstantSizeLambda() {
return shortLengthListConstantSize.stream().filter(s -> s.length() == 3).count();
}
@Benchmark
public long shortLengthConstantSizeLambdaParallel() {
return shortLengthListConstantSize.stream().parallel().filter(s -> s.length() == 3).count();
}
@Benchmark
public long mediumLengthConstantSizeFor() {
long count = 0;
for (String val : mediumLengthListConstantSize) {
if (val.length() == 3) { ++ count; }
}
return count;
}
@Benchmark
public long mediumLengthConstantSizeForEach() {
IntHolder intHolder = new IntHolder();
mediumLengthListConstantSize.forEach(s -> { if (s.length() == 3) ++ intHolder.value; } );
return intHolder.value;
}
@Benchmark
public long mediumLengthConstantSizeLambda() {
return mediumLengthListConstantSize.stream().filter(s -> s.length() == 3).count();
}
@Benchmark
public long mediumLengthConstantSizeLambdaParallel() {
return mediumLengthListConstantSize.stream().parallel().filter(s -> s.length() == 3).count();
}
@Benchmark
public long longerLengthConstantSizeFor() {
long count = 0;
for (String val : longerLengthListConstantSize) {
if (val.length() == 3) { ++ count; }
}
return count;
}
@Benchmark
public long longerLengthConstantSizeForEach() {
IntHolder intHolder = new IntHolder();
longerLengthListConstantSize.forEach(s -> { if (s.length() == 3) ++ intHolder.value; } );
return intHolder.value;
}
@Benchmark
public long longerLengthConstantSizeLambda() {
return longerLengthListConstantSize.stream().filter(s -> s.length() == 3).count();
}
@Benchmark
public long longerLengthConstantSizeLambdaParallel() {
return longerLengthListConstantSize.stream().parallel().filter(s -> s.length() == 3).count();
}
@Benchmark
public long longLengthConstantSizeFor() {
long count = 0;
for (String val : longLengthListConstantSize) {
if (val.length() == 3) { ++ count; }
}
return count;
}
@Benchmark
public long longLengthConstantSizeForEach() {
IntHolder intHolder = new IntHolder();
longLengthListConstantSize.forEach(s -> { if (s.length() == 3) ++ intHolder.value; } );
return intHolder.value;
}
@Benchmark
public long longLengthConstantSizeLambda() {
return longLengthListConstantSize.stream().filter(s -> s.length() == 3).count();
}
@Benchmark
public long longLengthConstantSizeLambdaParallel() {
return longLengthListConstantSize.stream().parallel().filter(s -> s.length() == 3).count();
}
public static class IntHolder {
public int value = 0;
}
}
我正在一台Windows 7笔记本电脑上运行这些程序。我不关心绝对的测量结果,只关心相对的。以下是它们的最新结果:
Benchmark Mode Cnt Score Error Units
MyBenchmark.longLengthConstantSizeFor thrpt 200 2984.554 ± 57.557 ops/s
MyBenchmark.longLengthConstantSizeForEach thrpt 200 2971.701 ± 110.414 ops/s
MyBenchmark.longLengthConstantSizeLambda thrpt 200 331.741 ± 2.196 ops/s
MyBenchmark.longLengthConstantSizeLambdaParallel thrpt 200 2827.695 ± 682.662 ops/s
MyBenchmark.longerLengthConstantSizeFor thrpt 200 3551842.518 ± 42612.744 ops/s
MyBenchmark.longerLengthConstantSizeForEach thrpt 200 3616285.629 ± 16335.379 ops/s
MyBenchmark.longerLengthConstantSizeLambda thrpt 200 2791292.093 ± 12207.302 ops/s
MyBenchmark.longerLengthConstantSizeLambdaParallel thrpt 200 50278.869 ± 1977.648 ops/s
MyBenchmark.mediumLengthConstantSizeFor thrpt 200 55447999.297 ± 277442.812 ops/s
MyBenchmark.mediumLengthConstantSizeForEach thrpt 200 57381287.954 ± 362751.975 ops/s
MyBenchmark.mediumLengthConstantSizeLambda thrpt 200 15925281.039 ± 65707.093 ops/s
MyBenchmark.mediumLengthConstantSizeLambdaParallel thrpt 200 60082.495 ± 581.405 ops/s
MyBenchmark.shortLengthConstantSizeFor thrpt 200 132278188.475 ± 1132184.820 ops/s
MyBenchmark.shortLengthConstantSizeForEach thrpt 200 124158664.044 ± 1112991.883 ops/s
MyBenchmark.shortLengthConstantSizeLambda thrpt 200 18750818.019 ± 171239.562 ops/s
MyBenchmark.shortLengthConstantSizeLambdaParallel thrpt 200 474054.951 ± 1344.705 ops/s
在早期的问题中,我确认这些基准测试似乎是“功能等效的”(只是寻求额外的眼睛)。这些数字是否与这些基准测试的独立运行相一致?
另一件我一直不确定的事情是JMH输出中究竟代表什么,特别是吞吐量数字。例如,“Cnt”列中的“200”到底代表什么?吞吐量单位是“每秒操作次数”,那么“操作”究竟代表什么,是执行一次基准测试方法的调用吗?例如,在最后一行中,这将代表一秒钟内对基准测试方法进行474k次执行。
更新:
我注意到当我将“for”与“lambda”进行比较时,从“short”列表开始到更长的列表,它们之间的比率非常大,但会逐渐降低,直到“long”列表,其中比率甚至比“short”列表还要大(14%,29%,78%和11%)。我觉得这很奇怪。我本来期望随着实际业务逻辑的工作量增加,流开销的比率会降低。您有任何想法吗?