[英]How to build a more efficient functional code ? Java FP
當我在Euler項目上訓練自己時,我幾乎沒有找到一種使用功能性方法解決問題5的方法。
目的是找到可被2到20的所有整數整除的數字。
我首先用經典Java解決了這一問題(我知道我的代碼不好用,對此感到抱歉),然后我想用FP獲得結果,認為效率會更高。
普通的舊Java花費了750毫秒才能找到結果。 流/ FP大約花費了750毫秒。
關於FP方式為什么需要這么多時間來完成,您是否有任何想法/解釋? 我猜我的代碼不是更好的代碼,不是普通的舊Java代碼還是FP代碼。
但是我想了解我在哪里肯定出錯了。
請注意,並行化Stream處理可獲得約130 ms(750 ms-> 620 ms)的收益。
注意2:從9699690L
(即: 2*3*5*7*9*11*13*17*19
)開始很好,但對於該應用程序來說似乎非常寬松(對於這兩個Plain Old Java而言)和FP方式)開始...為什么?
這是普通的舊Java代碼:
@Test
void test() {
long start = System.currentTimeMillis();
boolean foundValue = false;
long valueToFindOut = 20L;
List<Long> divisors = Arrays.asList(2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L,
19L, 20L);
while (!foundValue) {
boolean found = false;
for (long div : divisors) {
if (isDivisible(valueToFindOut, div)) {
found = true;
} else {
found = false;
break;
}
}
if (!found) {
valueToFindOut += 20L;
} else {
foundValue = true;
System.out.println("Valeur trouvée = " + valueToFindOut);
}
}
for (long div : divisors) {
assertTrue(isDivisible(valueToFindOut, div));
}
long end = System.currentTimeMillis();
System.out.println("Résultat obtenu en " + (end - start) + " millisecondes");
}
private boolean isDivisible(long toDivide, long divisor) {
return toDivide % divisor == 0;
}
功能代碼如下:
@Test
void testLambda() {
long start = System.currentTimeMillis();
List<Long> divisors = Arrays.asList(2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L,
19L, 20L);
Predicate<Long> predicate = longPredicate(divisors);
long result = generateLongStream().filter(predicate).findFirst().get();
long end = System.currentTimeMillis();
System.out.println("Resultat = " + result + " obtenu en " + (end - start) + " millisecondes.");
}
private boolean isDivisible(long toDivide, long divisor) {
return toDivide % divisor == 0;
}
private Stream<Long> generateLongStream() {
return Stream.iterate(20L, l -> l + 20L).parallel();
}
private Predicate<Long> longPredicate(List<Long> longs) {
long start = System.currentTimeMillis();
Predicate<Long> predicate = null;
if(!(longs.isEmpty())) {
List<Predicate<Long>> predicates = new ArrayList<Predicate<Long>>(longs.size());
longs.forEach(divisor -> {
predicates.add(valueToTest -> isDivisible(valueToTest, divisor));
});
for(int i = 0; i < predicates.size(); i++) {
if(i == 0) {
predicate = predicates.get(i);
} else {
predicate = predicate.and(predicates.get(i));
}
}
}
long end = System.currentTimeMillis();
System.out.println("Predicate construit en " + (end - start) + " millisecondes.");
return predicate;
}
預先感謝您的所有建議。
我們可以替換循環遍歷所有東西...
for( Thing thing : things ){
process(thing);
}
...具有更多功能...
things.forEach( thing -> process( thing ) );
...但是實際發生的情況非常相似:我們必須遍歷列表,為列表的每個元素調用process
方法。 功能版本甚至可能會稍微慢一些,因為在調用有用方法之前,有一個額外的方法調用lambda。
因此,我認為功能版本花費與原始版本相似的時間並不奇怪。
功能版本的優勢可能是
但是這些都不會對性能有所幫助。
首先,我將回答我的評論:在處理基於long
算法的算法時,應避免使用Long
並偏愛long。
您絕對不能忽略(取消)裝箱操作的成本:我使用long
, long[]
, LongPredicate
和LongStream
重寫了您的代碼,在我的Ryzen 7 2700X上它花費了以下時間:
┌─────────────────┬───────┐
│ Method │ Time │
├─────────────────┼───────┤
│ LongStream │ 129ms │
│ Old Java (Long) │ 336ms │
│ Old Java (long) │ 273ms │
└─────────────────┴───────┘
下面給出了實現(很抱歉,如果時間太長,我不知道如何將文件附加到Stackoverflow,並且我認為pastebin也不會這樣做)。
LongStream
方法是這里的贏家,但是我認為基准是錯誤的:
System::currentTimeMillis
替補。 此方法返回當前時間,該時間可能會更改(例如,由於NTP調整了時鍾)。 您必須使用System::nanoTime
。 longPredicate
方法做了太多的工作:
List<Predicate>
即可將其轉換為一個Predicate
。 predicate = predicate.and(...)
。 請注意,由於您將無法引用i
,因此我必須使用返回lambda的方法:
for (int i = 1; i < longs.length; ++i) {
predicate = predicate.and(n -> isDisivisble(n, longs[i])); // fail because i is not final
}
您還可以創建一個新的局部變量(這是通過我的方法中的參數完成的。)
因此,這是JMH給出的結果:
┌─────────────────────────────────┬────────┬───────┬───────────┬───────────┬────────┐
│ Benchmark │ Mode │ Cnt │ Score │ Error │ Units │
├─────────────────────────────────┼────────┼───────┼───────────┼───────────┼────────┤
│ PlainOldJavaLongPrimitive.test │ avgt │ 10 │ 188,072 │ 1,002 │ ms/op │
│ PlainOldJavaLongWrapper.test │ avgt │ 10 │ 265,649 │ 0,920 │ ms/op │
│ StreamLongPrimitive.testLambda │ avgt │ 10 │ 86,046 │ 1,829 │ ms/op │
│ StreamLongWrapper.testLambda │ avgt │ 10 │ 230,158 │ 34,122 │ ms/op │
│ PlainOldJavaLongPrimitive.test │ ss │ 10 │ 198,192 │ 37,573 │ ms/op │
│ PlainOldJavaLongWrapper.test │ ss │ 10 │ 268,587 │ 7,378 │ ms/op │
│ StreamLongPrimitive.testLambda │ ss │ 10 │ 116,108 │ 65,161 │ ms/op │
│ StreamLongWrapper.testLambda │ ss │ 10 │ 532,534 │ 335,032 │ ms/op │
└─────────────────────────────────┴────────┴───────┴───────────┴───────────┴────────┘
-
要運行此JMH項目:
mvn install
java -jar target/microbenchmarks.jar -rff bench
文件:
/pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.stackoverflow.nodatafound</groupId>
<artifactId>stackoverflow-56622173</artifactId>
<version>1</version>
<packaging>jar</packaging>
<properties>
<project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>${project.build.sourceEncoding}</project.reporting.outputEncoding>
<maven.compiler.release>11</maven.compiler.release>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<version>1.21</version>
</dependency>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-generator-annprocess</artifactId>
<version>1.21</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-enforcer-plugin</artifactId>
<version>3.0.0-M2</version>
<executions>
<execution>
<id>enforce-maven</id>
<inherited>true</inherited>
<goals>
<goal>enforce</goal>
</goals>
<configuration>
<rules>
<requireMavenVersion>
<version>[3.6.1,)</version>
</requireMavenVersion>
<requireJavaVersion>
<version>[11.0.0,)</version>
</requireJavaVersion>
</rules>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.1</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<finalName>microbenchmarks</finalName>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>org.openjdk.jmh.Main</mainClass>
</transformer>
</transformers>
<filters>
<filter>
<artifact>*:*</artifact>
<excludes>
<exclude>META-INF/services/javax.annotation.processing.Processor</exclude>
</excludes>
</filter>
</filters>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
/src/main/java/com/stackoverflow/nodatafound/q56622173/PlainOldJavaLongPrimitive.java
package com.stackoverflow.nodatafound.q56622173;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
@State(Scope.Benchmark)
@Warmup(iterations = 2)
@Fork(1)
@Measurement(iterations = 10)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@BenchmarkMode({ Mode.AverageTime, Mode.SingleShotTime })
public class PlainOldJavaLongPrimitive {
@Benchmark
public Object test() {
boolean foundValue = false;
long valueToFindOut = 20L;
final long[] divisors = new long[] { 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L,
19L, 20L };
while (!foundValue) {
boolean found = false;
for (final long div : divisors) {
if (isDivisible(valueToFindOut, div)) {
found = true;
} else {
found = false;
break;
}
}
if (!found) {
valueToFindOut += 20L;
} else {
foundValue = true;
}
}
for (final long div : divisors) {
if (!isDivisible(valueToFindOut, div)) {
throw new AssertionError("valueToFindOut: " + valueToFindOut + ", div: " + div);
}
}
return Long.valueOf(valueToFindOut);
}
private boolean isDivisible(final long toDivide, final long divisor) {
return toDivide % divisor == 0;
}
}
/src/main/java/com/stackoverflow/nodatafound/q56622173/PlainOldJavaLongWrapper.java
package com.stackoverflow.nodatafound.q56622173;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
@State(Scope.Benchmark)
@Warmup(iterations = 2)
@Fork(1)
@Measurement(iterations = 10)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@BenchmarkMode({ Mode.AverageTime, Mode.SingleShotTime })
public class PlainOldJavaLongWrapper {
@Benchmark
public Object test() {
boolean foundValue = false;
long valueToFindOut = 20L;
final List<Long> divisors = Arrays.asList(2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L,
18L, 19L, 20L);
while (!foundValue) {
boolean found = false;
for (final long div : divisors) {
if (isDivisible(valueToFindOut, div)) {
found = true;
} else {
found = false;
break;
}
}
if (!found) {
valueToFindOut += 20L;
} else {
foundValue = true;
}
}
for (final long div : divisors) {
if (!isDivisible(valueToFindOut, div)) {
throw new AssertionError("valueToFindOut: " + valueToFindOut + ", div: " + div);
}
}
return Long.valueOf(valueToFindOut);
}
private boolean isDivisible(final long toDivide, final long divisor) {
return toDivide % divisor == 0;
}
}
/src/main/java/com/stackoverflow/nodatafound/q56622173/StreamLongPrimitive.java
package com.stackoverflow.nodatafound.q56622173;
import java.util.concurrent.TimeUnit;
import java.util.function.LongPredicate;
import java.util.stream.LongStream;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
@State(Scope.Benchmark)
@Warmup(iterations = 2)
@Fork(1)
@Measurement(iterations = 10)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@BenchmarkMode({ Mode.AverageTime, Mode.SingleShotTime })
public class StreamLongPrimitive {
@Benchmark
public Object testLambda() {
final long[] divisors = new long[] { 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L,
19L, 20L };
final LongPredicate predicate = longPredicate(divisors);
return generateLongStream().filter(predicate).findFirst().getAsLong();
}
private LongPredicate divisiblePredicate(final long divisor) {
return n -> n % divisor == 0;
}
private LongStream generateLongStream() {
return LongStream.iterate(20L, l -> l + 20L).parallel();
}
private LongPredicate longPredicate(final long[] longs) {
if (longs.length == 0) {
throw new IllegalArgumentException("Pas de diviseurs");
}
LongPredicate predicate = divisiblePredicate(longs[0]);
for (int i = 1; i < longs.length; ++i) {
predicate = predicate.and(divisiblePredicate(longs[i]));
}
return predicate;
}
}
/src/main/java/com/stackoverflow/nodatafound/q56622173/StreamLongWrapper.java
package com.stackoverflow.nodatafound.q56622173;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.function.Predicate;
import java.util.stream.Stream;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
@State(Scope.Benchmark)
@Warmup(iterations = 2)
@Fork(1)
@Measurement(iterations = 10)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@BenchmarkMode({ Mode.AverageTime, Mode.SingleShotTime })
public class StreamLongWrapper {
@Benchmark
public Object testLambda() {
final List<Long> divisors = Arrays.asList(2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L,
18L, 19L, 20L);
final Predicate<Long> predicate = longPredicate(divisors);
return generateLongStream().filter(predicate).findFirst().get();
}
private boolean isDivisible(final long toDivide, final long divisor) {
return toDivide % divisor == 0;
}
private Stream<Long> generateLongStream() {
return Stream.iterate(20L, l -> l + 20L).parallel();
}
private Predicate<Long> longPredicate(final List<Long> longs) {
if (longs.isEmpty()) {
throw new IllegalArgumentException("Pas de diviseurs");
}
final List<Predicate<Long>> predicates = new ArrayList<>(longs.size());
longs.forEach(divisor -> {
predicates.add(valueToTest -> isDivisible(valueToTest, divisor));
});
Predicate<Long> predicate = predicates.get(0);
for (int i = 1; i < predicates.size(); i++) {
predicate = predicate.and(predicates.get(i));
}
return predicate;
}
}
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