Stream.toList() 的性能会比 Collectors.toList() 更好吗?

2022-09-03 06:18:01

JDK 正在引入带有 JDK-8180352 的 API Stream.toList()。这是一个基准测试代码,我试图将其性能与现有代码进行比较:Collectors.toList

@BenchmarkMode(Mode.All)
@Fork(1)
@State(Scope.Thread)
@Warmup(iterations = 20, time = 1, batchSize = 10000)
@Measurement(iterations = 20, time = 1, batchSize = 10000)
public class CollectorsVsStreamToList {

    @Benchmark
    public List<Integer> viaCollectors() {
        return IntStream.range(1, 1000).boxed().collect(Collectors.toList());
    }

    @Benchmark
    public List<Integer> viaStream() {
        return IntStream.range(1, 1000).boxed().toList();
    }
}

结果摘要如下:

Benchmark                                                       Mode  Cnt   Score    Error  Units
CollectorsVsStreamToList.viaCollectors                         thrpt   20  17.321 ±  0.583  ops/s
CollectorsVsStreamToList.viaStream                             thrpt   20  23.879 ±  1.682  ops/s
CollectorsVsStreamToList.viaCollectors                          avgt   20   0.057 ±  0.002   s/op
CollectorsVsStreamToList.viaStream                              avgt   20   0.040 ±  0.001   s/op
CollectorsVsStreamToList.viaCollectors                        sample  380   0.054 ±  0.001   s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.00    sample        0.051            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.50    sample        0.054            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.90    sample        0.058            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.95    sample        0.058            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.99    sample        0.062            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.999   sample        0.068            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p0.9999  sample        0.068            s/op
CollectorsVsStreamToList.viaCollectors:viaCollectors·p1.00    sample        0.068            s/op
CollectorsVsStreamToList.viaStream                            sample  525   0.039 ±  0.001   s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.00            sample        0.037            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.50            sample        0.038            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.90            sample        0.040            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.95            sample        0.042            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.99            sample        0.050            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.999           sample        0.051            s/op
CollectorsVsStreamToList.viaStream:viaStream·p0.9999          sample        0.051            s/op
CollectorsVsStreamToList.viaStream:viaStream·p1.00            sample        0.051            s/op
CollectorsVsStreamToList.viaCollectors                            ss   20   0.060 ±  0.007   s/op
CollectorsVsStreamToList.viaStream                                ss   20   0.043 ±  0.006   s/op

当然,领域专家面临的第一个问题是基准测试程序是否正确?测试类是在 MacOS 上执行的。请让我知道所需的任何进一步细节。

随访,就我从读数中可以推断出的平均时间、通量和采样时间看起来比.这种理解是否正确?Stream.toListCollectors.toList


答案 1

Stream::toList建在上面,而不是 。有许多优化,使其可能比收集更快,尽管这在很大程度上取决于细节。如果流管道(从源到最终中间操作)是 ,则可以预先调整目标阵列的大小(而不是像收集器必须做的那样重新分配)。如果管道更远,那么并行执行不仅可以预先调整结果数组的大小,还可以计算出精确的每分片偏移量,因此每个子任务都可以将其结果放在正确的位置,从而无需将中间结果复制到最终结果中。toArraycollecttoArraySIZEDtoListSUBSIZED

因此,根据细节,可能比 快得多。toListcollect


答案 2

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