使用goroutine组合

Question

I'm trying to get a code to work that pretty much involves channels in goroutine (in a yield-like behavior in C#)

The code involves getting an iterable matrix from a slice like so:

elements := []float64{1, 2, 3, 4}

expected := [][]float64{
    {1},
    {2},
    {3},
    {4},
    {1, 2},
    {1, 3},
    {2, 3},
    {1, 4},
    {2, 4},
    {3, 4},
    {1, 2, 3},
    {1, 2, 4},
    {1, 3, 4},
    {2, 3, 4},
    {1, 2, 3, 4},
}

I've tried applying Knuth's by doing:

func Combinadic(values []float64) <-chan []float64 {
    ch := make(chan []float64)
    go func() {
        for i := 0; i < len(values); i++ {

            for value := range CombinadicK(values, i+1) {
                ch <- value
            }

        }
        close(ch)
    }()

    return ch

}

func CombinadicK(values []float64, k int) <-chan []float64 {
    chnl := make(chan []float64)
    go func() {
        n := len(values)

        t := k

        c := make([]int, t+3)
        current := make([]float64, t)

        x := 0
        j := 0

        for j = 1; j <= t; j++ {
            c[j] = j - 1
        }

        c[t+1] = n
        c[t+2] = 0

        j = t

        for {
            for i := 0; i < len(current); i++ {
                current[i] = values[c[i+1]]
            }

            chnl <- current

            if j > 0 {
                x = j
            } else {
                if c[1]+1 < c[2] {
                    c[1]++
                    continue
                } else {
                    j = 2
                }
            }

            for {
                c[j-1] = j - 2
                x = c[j] + 1
                if x == c[j+1] {
                    j++
                } else {
                    break
                }
            }

            c[j] = x
            j--

            if j >= t {
                break
            }
        }

        close(chnl)
    }()

    return chnl
}

It appears to give out random number per row, but the structure of the expected (the count of items per row) appears to be ok.

The code in Go Playground

Answer 1

You have a data race. Your results are undefined.

$ go run -race racer.go
==================
WARNING: DATA RACE
Read at 0x00c00009c010 by main goroutine:
  reflect.typedmemmove()
      /home/peter/go/src/runtime/mbarrier.go:177 +0x0
  reflect.packEface()
      /home/peter/go/src/reflect/value.go:119 +0x103
  reflect.valueInterface()
      /home/peter/go/src/reflect/value.go:1027 +0x16f
  fmt.(*pp).printValue()
      /home/peter/go/src/reflect/value.go:997 +0x38f7
  fmt.(*pp).printValue()
      /home/peter/go/src/fmt/print.go:868 +0xec7
  fmt.(*pp).printArg()
      /home/peter/go/src/fmt/print.go:715 +0x2ee
  fmt.(*pp).doPrintln()
      /home/peter/go/src/fmt/print.go:1172 +0xad
  fmt.Fprintln()
      /home/peter/go/src/fmt/print.go:263 +0x65
  main.main()
      /home/peter/go/src/fmt/print.go:273 +0x14b

Previous write at 0x00c00009c010 by goroutine 8:
  main.CombinadicK.func1()
      /home/peter/racer.go:48 +0x1e6

Goroutine 8 (running) created at:
  main.CombinadicK()
      /home/peter/racer.go:26 +0x96
  main.Combinadic.func1()
      /home/peter/racer.go:12 +0xda
==================
[3]
[3]
[4]
[4]
[2 3]
[2 4]
[1 4]
[3 4]
[3 4]
[3 4]
[1 3 4]
[1 3 4]
[1 3 4]
[2 3 4]
[1 2 3 4]
Found 1 data race(s)
exit status 66
$ 

racer.go:

package main

import (
    "fmt"
)

func Combinadic(values []float64) <-chan []float64 {
    ch := make(chan []float64)
    go func() {
        for i := 0; i < len(values); i++ {

            for value := range CombinadicK(values, i+1) {
                ch <- value
            }

        }
        close(ch)
    }()

    return ch

}

func CombinadicK(values []float64, k int) <-chan []float64 {
    chnl := make(chan []float64)
    go func() {
        n := len(values)

        t := k

        c := make([]int, t+3)
        current := make([]float64, t)

        x := 0
        j := 0

        for j = 1; j <= t; j++ {
            c[j] = j - 1
        }

        c[t+1] = n
        c[t+2] = 0

        j = t

        for {
            for i := 0; i < len(current); i++ {
                current[i] = values[c[i+1]]
            }

            chnl <- current

            if j > 0 {
                x = j
            } else {
                if c[1]+1 < c[2] {
                    c[1]++
                    continue
                } else {
                    j = 2
                }
            }

            for {
                c[j-1] = j - 2
                x = c[j] + 1
                if x == c[j+1] {
                    j++
                } else {
                    break
                }
            }

            c[j] = x
            j--

            if j >= t {
                break
            }
        }

        close(chnl)
    }()

    return chnl
}

func main() {
    elements := []float64{1, 2, 3, 4}
    for v := range Combinadic(elements) {
        fmt.Println(v)
    }
}

Playground: https://play.golang.org/p/hhQgVdqe6l1

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Go: Data Race Detector