kotlin - 第一次调用 `ArraysKt.contains` 很慢

Question

考虑一下:

import kotlin.system.measureTimeMillis

fun main() {
  // Uncomment, and make it >=2 elements will make [timeInMillis] 0.
  // Changing [setOf] to [arrayOf] doesn't help.
  // setOf(1, 2)

  val timeInMillis = measureTimeMillis {
    3 in arrayOf(4)
  }
  println("$timeInMillis ms")
}

我相信 arrayOf(4) 中的 3 相当于 ArraysKt.contains(new Integer[]{4}, 3); Java 代码。

出于某种原因，在 JVM 中的 Linux 上，timeInMillis 最多可能需要 30 毫秒。我在对 Android 上的同等产品进行基准测试时发现了这一点，在 Pixel 2 设备上，它可能需要长达 90 毫秒的时间。考虑到工作量，这些数字似乎相当大。

我的猜测是 Kotlin stdlib 中正在进行某种惰性初始化，从而导致了这种情况。我如何了解更多有关正在发生的事情？

Answer 1

My guess is that there's some sort of lazy initialization going on in Kotlin stdlib which causes this.

确实存在延迟初始化，这与 Kotlin 无关，而是与 JVM 有关。这就是 JVM 加载类的方式。您可以使用 -verbose:class JVM 选项来找出哪些类已初​​始化。

println("Measure Start!")
val timeInMillis = measureNanoTime {
    3 in arrayOf(4)
}
println("Measure End!")
println("$timeInMillis ns")

在我的 macOS 机器上使用 IntelliJ 运行此命令并使用 -verbose:class 打印(仅显示输出的相关部分):

Measure Start!
[0.132s][info][class,load] java.net.SocketAddress source: jrt:/java.base
[0.132s][info][class,load] java.net.InetSocketAddress source: jrt:/java.base
[0.132s][info][class,load] java.net.InetAddress source: shared objects file
[0.133s][info][class,load] jdk.internal.access.JavaNetInetAddressAccess source: shared objects file
[0.133s][info][class,load] java.net.InetAddress$1 source: shared objects file
[0.133s][info][class,load] java.net.InetAddress$InetAddressHolder source: shared objects file
[0.133s][info][class,load] java.util.SortedSet source: shared objects file
[0.133s][info][class,load] java.util.NavigableSet source: shared objects file
[0.133s][info][class,load] java.util.concurrent.ConcurrentSkipListSet source: shared objects file
[0.134s][info][class,load] java.util.SortedMap source: shared objects file
[0.134s][info][class,load] java.util.NavigableMap source: shared objects file
[0.134s][info][class,load] java.util.concurrent.ConcurrentNavigableMap source: shared objects file
[0.134s][info][class,load] java.util.concurrent.ConcurrentSkipListMap source: shared objects file
[0.134s][info][class,load] java.util.concurrent.ConcurrentSkipListMap$Index source: shared objects file
[0.134s][info][class,load] java.util.concurrent.atomic.Striped64 source: shared objects file
[0.134s][info][class,load] java.util.concurrent.atomic.LongAdder source: shared objects file
[0.134s][info][class,load] java.util.concurrent.ConcurrentSkipListMap$Node source: shared objects file
[0.134s][info][class,load] java.net.InetAddressImplFactory source: shared objects file
[0.134s][info][class,load] java.net.InetAddressImpl source: shared objects file
[0.134s][info][class,load] java.net.Inet6AddressImpl source: shared objects file
[0.134s][info][class,load] java.lang.Class$1 source: shared objects file
[0.135s][info][class,load] java.net.InetAddress$NameService source: shared objects file
[0.135s][info][class,load] java.net.InetAddress$PlatformNameService source: shared objects file
[0.135s][info][class,load] java.net.Inet4Address source: shared objects file
[0.135s][info][class,load] java.net.InetSocketAddress$InetSocketAddressHolder source: jrt:/java.base
[0.135s][info][class,load] java.net.SocketOptions source: jrt:/java.base
[0.135s][info][class,load] java.net.SocketImpl source: jrt:/java.base
[0.136s][info][class,load] java.net.SocketImpl$$Lambda$14/0x0000000800b69840 source: java.net.SocketImpl
[0.136s][info][class,load] sun.net.NetProperties source: jrt:/java.base
[0.136s][info][class,load] sun.net.NetProperties$1 source: jrt:/java.base
[0.136s][info][class,load] java.util.Properties$LineReader source: shared objects file
[0.137s][info][class,load] sun.net.PlatformSocketImpl source: jrt:/java.base
[0.138s][info][class,load] sun.nio.ch.NioSocketImpl source: jrt:/java.base
[0.138s][info][class,load] sun.nio.ch.NativeDispatcher source: jrt:/java.base
[0.138s][info][class,load] sun.nio.ch.SocketDispatcher source: jrt:/java.base
[0.138s][info][class,load] sun.nio.ch.IOUtil source: jrt:/java.base
[0.140s][info][class,load] java.util.concurrent.locks.AbstractQueuedSynchronizer source: shared objects file
[0.140s][info][class,load] java.util.concurrent.locks.ReentrantLock$Sync source: shared objects file
[0.140s][info][class,load] java.util.concurrent.locks.ReentrantLock$NonfairSync source: shared objects file
[0.140s][info][class,load] java.net.SocksConsts source: jrt:/java.base
[0.140s][info][class,load] java.net.DelegatingSocketImpl source: jrt:/java.base
[0.140s][info][class,load] java.net.SocksSocketImpl source: jrt:/java.base
[0.140s][info][class,load] sun.nio.ch.Net source: jrt:/java.base
[0.140s][info][class,load] java.net.ProtocolFamily source: jrt:/java.base
[0.140s][info][class,load] sun.nio.ch.Net$1 source: jrt:/java.base
[0.141s][info][class,load] sun.net.ext.ExtendedSocketOptions source: jrt:/java.base
[0.141s][info][class,load] jdk.net.ExtendedSocketOptions source: jrt:/jdk.net
[0.141s][info][class,load] java.net.SocketOption source: jrt:/java.base
[0.141s][info][class,load] jdk.net.ExtendedSocketOptions$ExtSocketOption source: jrt:/jdk.net
[0.141s][info][class,load] jdk.net.SocketFlow source: jrt:/jdk.net
[0.141s][info][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions source: jrt:/jdk.net
[0.141s][info][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions$1 source: jrt:/jdk.net
[0.141s][info][class,load] jdk.net.MacOSXSocketOptions source: jrt:/jdk.net
[0.143s][info][class,load] kotlin.collections.ArraysKt__ArraysJVMKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] kotlin.collections.ArraysKt__ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] kotlin.collections.ArraysKt___ArraysJvmKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] kotlin.collections.ArraysKt___ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] kotlin.collections.ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] jdk.net.ExtendedSocketOptions$1 source: jrt:/jdk.net
[0.144s][info][class,load] java.net.Inet6Address source: shared objects file
[0.145s][info][class,load] java.net.Inet6Address$Inet6AddressHolder source: shared objects file
[0.151s][info][class,load] kotlin.jvm.internal.Intrinsics source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.151s][info][class,load] kotlin.KotlinNullPointerException source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.152s][info][class,load] kotlin.UninitializedPropertyAccessException source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.152s][info][class,load] java.lang.AssertionError source: jrt:/java.base
[0.152s][info][class,load] java.lang.IllegalStateException source: jrt:/java.base
[0.152s][info][class,load] java.lang.UnsupportedOperationException source: jrt:/java.base
[0.152s][info][class,load] java.net.StandardProtocolFamily source: jrt:/java.base
Measure End!
20704379 ns

记下时间戳。

当您在 arrayOf(4) 中执行 3 时，加载了很多类，因为这是您第一次使用这些类。请特别注意 kotlin.collections.ArraysKt 已加载。

如果你先这样做怎么办？

println("Calling setOf")
println(setOf(1, 2))

输出变为:

Calling setOf
[0.126s][info][class,load] jdk.internal.access.JavaNetInetAddressAccess source: shared objects file
[0.126s][info][class,load] java.net.InetAddress$1 source: shared objects file
[0.126s][info][class,load] java.net.InetAddress$InetAddressHolder source: shared objects file
[0.126s][info][class,load] java.util.SortedSet source: shared objects file
[0.126s][info][class,load] java.util.NavigableSet source: shared objects file
[0.126s][info][class,load] java.util.concurrent.ConcurrentSkipListSet source: shared objects file
[0.126s][info][class,load] java.util.SortedMap source: shared objects file
[0.126s][info][class,load] java.util.NavigableMap source: shared objects file
[0.126s][info][class,load] java.util.concurrent.ConcurrentNavigableMap source: shared objects file
[0.126s][info][class,load] java.util.concurrent.ConcurrentSkipListMap source: shared objects file
[0.126s][info][class,load] java.util.concurrent.ConcurrentSkipListMap$Index source: shared objects file
[0.126s][info][class,load] java.util.concurrent.atomic.Striped64 source: shared objects file
[0.126s][info][class,load] java.util.concurrent.atomic.LongAdder source: shared objects file
[0.126s][info][class,load] java.util.concurrent.ConcurrentSkipListMap$Node source: shared objects file
[0.126s][info][class,load] java.net.InetAddressImplFactory source: shared objects file
[0.127s][info][class,load] java.net.InetAddressImpl source: shared objects file
[0.127s][info][class,load] java.net.Inet6AddressImpl source: shared objects file
[0.127s][info][class,load] kotlin.collections.SetsKt__SetsJVMKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.127s][info][class,load] kotlin.collections.SetsKt__SetsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.127s][info][class,load] java.lang.Class$1 source: shared objects file
[0.127s][info][class,load] kotlin.collections.SetsKt___SetsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.127s][info][class,load] kotlin.collections.SetsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.127s][info][class,load] java.net.InetAddress$NameService source: shared objects file
[0.127s][info][class,load] java.net.InetAddress$PlatformNameService source: shared objects file
[0.127s][info][class,load] java.net.Inet4Address source: shared objects file
[0.127s][info][class,load] java.net.InetSocketAddress$InetSocketAddressHolder source: jrt:/java.base
[0.128s][info][class,load] java.net.SocketOptions source: jrt:/java.base
[0.128s][info][class,load] java.net.SocketImpl source: jrt:/java.base
[0.128s][info][class,load] kotlin.jvm.internal.Intrinsics source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.128s][info][class,load] java.net.SocketImpl$$Lambda$14/0x0000000800b6a040 source: java.net.SocketImpl
[0.128s][info][class,load] kotlin.KotlinNullPointerException source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.129s][info][class,load] sun.net.NetProperties source: jrt:/java.base
[0.129s][info][class,load] sun.net.NetProperties$1 source: jrt:/java.base
[0.129s][info][class,load] java.util.Properties$LineReader source: shared objects file
[0.129s][info][class,load] kotlin.UninitializedPropertyAccessException source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.129s][info][class,load] java.lang.AssertionError source: jrt:/java.base
[0.129s][info][class,load] java.lang.IllegalStateException source: jrt:/java.base
[0.129s][info][class,load] java.lang.UnsupportedOperationException source: jrt:/java.base
[0.130s][info][class,load] sun.net.PlatformSocketImpl source: jrt:/java.base
[0.130s][info][class,load] sun.nio.ch.NioSocketImpl source: jrt:/java.base
[0.130s][info][class,load] sun.nio.ch.NativeDispatcher source: jrt:/java.base
[0.130s][info][class,load] sun.nio.ch.SocketDispatcher source: jrt:/java.base
[0.130s][info][class,load] sun.nio.ch.IOUtil source: jrt:/java.base
[0.132s][info][class,load] java.util.concurrent.locks.AbstractQueuedSynchronizer source: shared objects file
[0.132s][info][class,load] java.util.concurrent.locks.ReentrantLock$Sync source: shared objects file
[0.132s][info][class,load] java.util.concurrent.locks.ReentrantLock$NonfairSync source: shared objects file
[0.132s][info][class,load] java.net.SocksConsts source: jrt:/java.base
[0.132s][info][class,load] java.net.DelegatingSocketImpl source: jrt:/java.base
[0.132s][info][class,load] java.net.SocksSocketImpl source: jrt:/java.base
[0.133s][info][class,load] sun.nio.ch.Net source: jrt:/java.base
[0.133s][info][class,load] java.net.ProtocolFamily source: jrt:/java.base
[0.133s][info][class,load] sun.nio.ch.Net$1 source: jrt:/java.base
[0.133s][info][class,load] sun.net.ext.ExtendedSocketOptions source: jrt:/java.base
[0.133s][info][class,load] jdk.net.ExtendedSocketOptions source: jrt:/jdk.net
[0.133s][info][class,load] java.net.SocketOption source: jrt:/java.base
[0.133s][info][class,load] jdk.net.ExtendedSocketOptions$ExtSocketOption source: jrt:/jdk.net
[0.133s][info][class,load] jdk.net.SocketFlow source: jrt:/jdk.net
[0.133s][info][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions source: jrt:/jdk.net
[0.133s][info][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions$1 source: jrt:/jdk.net
[0.133s][info][class,load] jdk.net.MacOSXSocketOptions source: jrt:/jdk.net
[0.135s][info][class,load] jdk.net.ExtendedSocketOptions$1 source: jrt:/jdk.net
[0.136s][info][class,load] java.net.Inet6Address source: shared objects file
[0.136s][info][class,load] java.net.Inet6Address$Inet6AddressHolder source: shared objects file
[0.139s][info][class,load] kotlin.collections.ArraysKt__ArraysJVMKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.139s][info][class,load] kotlin.collections.ArraysKt__ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.139s][info][class,load] kotlin.collections.ArraysKt___ArraysJvmKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.139s][info][class,load] kotlin.collections.ArraysKt___ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.139s][info][class,load] kotlin.collections.ArraysKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.143s][info][class,load] java.net.StandardProtocolFamily source: jrt:/java.base
[0.146s][info][class,load] sun.nio.ch.NioSocketImpl$$Lambda$15/0x0000000800b6a440 source: sun.nio.ch.NioSocketImpl
[0.146s][info][class,load] java.net.SocksSocketImpl$3 source: jrt:/java.base
[0.146s][info][class,load] java.net.ProxySelector source: jrt:/java.base
[0.146s][info][class,load] sun.net.spi.DefaultProxySelector source: jrt:/java.base
[0.146s][info][class,load] java.net.Proxy source: jrt:/java.base
[0.147s][info][class,load] java.net.Proxy$Type source: jrt:/java.base
[0.147s][info][class,load] sun.net.spi.DefaultProxySelector$1 source: jrt:/java.base
[0.147s][info][class,load] sun.net.spi.DefaultProxySelector$NonProxyInfo source: jrt:/java.base
[0.147s][info][class,load] sun.net.spi.DefaultProxySelector$3 source: jrt:/java.base
[0.147s][info][class,load] sun.net.NetHooks source: jrt:/java.base
[0.147s][info][class,load] sun.net.NetHooks$Provider source: jrt:/java.base
[0.147s][info][class,load] sun.net.sdp.SdpProvider source: jrt:/java.base
[0.148s][info][class,load] sun.nio.ch.NativeThread source: jrt:/java.base
[0.150s][info][class,load] kotlin.collections.MapsKt__MapWithDefaultKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.150s][info][class,load] kotlin.collections.MapsKt__MapsJVMKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.150s][info][class,load] kotlin.collections.MapsKt__MapsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.150s][info][class,load] kotlin.collections.MapsKt___MapsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.150s][info][class,load] kotlin.collections.MapsKt source: file:/Applications/IntelliJ%20IDEA%20CE.app/Contents/plugins/Kotlin/kotlinc/lib/kotlin-stdlib.jar
[0.150s][info][class,load] java.util.LinkedHashMap$LinkedKeySet source: jrt:/java.base
[0.151s][info][class,load] java.util.LinkedHashMap$LinkedHashIterator source: shared objects file
[0.151s][info][class,load] java.util.LinkedHashMap$LinkedKeyIterator source: jrt:/java.base
[1, 2]
Measure Start!
Measure End!
19515 ns

正如您所看到的，现在所有类加载都在开始测量之前完成。具体来说，kotlin.collections.ArraysKt 也已在此处加载(0.139 秒)。

但是，如果您首先调用 arrayOf 而不是 setOf，则它不会有效地工作，因为 arrayOf 是 内联。 Kotlin 编译器直接将 arrayOf(1, 2) 翻译为 new Integer[] { 1, 2 }，它不使用 ArraysKt 中的任何内容>，因此它不会导致 ArraysKt 被加载。

如果您使用一个元素调用 setOf，则会发生类似的情况。单个参数 setOf 调用 java.util.Collections.singleton，因此它不会使用 ArraysKt 中的任何内容:(

您还可以尝试使用 JVM 选项 -XX:+PrintCompilation。它向您显示每个方法何时进行 JIT 编译。 JIT 编译方法所需的时间也可能是第一次调用 in 速度慢的原因。

另请参阅:Why does the JVM require warmup?