编译二进制文件比运行“ go run”要慢

Question

I'm trying to solve the advent of code puzzles (so spoiler alert for those of you who haven't completed day 1), and I encountered something which I can't wrap my head around.

I have a function which generates a list of numbers based on some other list of numbers, and it returns the first number which is encountered for the second time:

func findFirstDoubleFrequency(freqs []int) int {
    seen := map[int]bool{0: true}
    freq := 0

    for {
        for _, f := range freqs {
            freq += f

            if seen[freq] == true {
                return freq
            }

            seen[freq] = true
        }
    }
}

When I run my code with go run, the function takes ~15ms to complete. But when I build an executable with go build and run that, it takes ~40ms to complete. I really would like to know why there is such a difference in execution time between those runs. Shouldn't they be the same? Or is something like GC slowing things down with the go build executable?

Answer 1

Stack Overflow

Questions seeking debugging help ("why isn't this code working?") must include the desired behavior, a specific problem or error and the shortest code necessary to reproduce it in the question itself.

---

Your benchmark is invalid. It's incomplete. It's not reproducible.

---

In Go, use the testing package to benchmark code. For example,

package main

import (
    "math/rand"
    "testing"
)

func findFirstDoubleFrequency(freqs []int) int {
    seen := map[int]bool{0: true}
    freq := 0

    for {
        for _, f := range freqs {
            freq += f

            if seen[freq] == true {
                return freq
            }

            seen[freq] = true
        }
    }
}

func BenchmarkFirstFrequency(b *testing.B) {
    freqs := make([]int, 1000)
    for i := range freqs {
        freqs[i] = rand.Intn(len(freqs)/10)
    }
    b.ReportAllocs()
    b.ResetTimer()
    for N := 0; N < b.N; N++ {
        findFirstDoubleFrequency(freqs)
    }
}

Output:

$ go test t94_test.go -bench=.
goos: linux
goarch: amd64
BenchmarkFirstFrequency-4        1000000    7206 ns/op    3342 B/op    16 allocs/op
$ 

---

WARNING: You have a possibly infinite loop:

package main

import (
    "math/rand"
    "testing"
)

func findFirstDoubleFrequency(freqs []int) int {
    seen := map[int]bool{0: true}
    freq := 0

    for {
        for _, f := range freqs {
            freq += f

            if seen[freq] == true {
                return freq
            }

            seen[freq] = true
        }
    }
}

func BenchmarkFirstFrequency(b *testing.B) {
    freqs := make([]int, 1000)
    for i := range freqs {
        freqs[i] = rand.Intn(len(freqs))
    }
    b.ReportAllocs()
    b.ResetTimer()
    for N := 0; N < b.N; N++ {
        findFirstDoubleFrequency(freqs)
    }
}

Output:

$ go test t94_test.go -bench=.
goos: linux
goarch: amd64
BenchmarkFirstFrequency-4       fatal error: runtime: out of memory