for-loop - 并行 For 循环

Question

我希望 for 循环使用 go 例程并行。我尝试使用 channel ，但没有用。我的主要问题是，我想在继续之前等待所有迭代完成。这就是为什么在它不起作用之前简单地编写 go 的原因。我尝试使用 channel (我认为是错误的方式)但这让我的代码变得更慢

func createPopulation(populationSize int, individualSize int) []Individual {
    population := make([]Individual, populationSize)

    //i want this loop to be work parallel
    for i := 0; i < len(population); i++ {
        population[i] = createIndividual(individualSize)
    }

    return population
}

func createIndividual(size int) Individual {
    var individual = Individual{make([]bool, size), 0}

    for i := 0; i < len(individual.gene); i++ {
        if rand.Intn(2)%2 == 1 {
            individual.gene[i] = true
        } else {
            individual.gene[i] = false
        }
    }

    return individual
}

我的结构看起来像这样:

type Individual struct {
    gene []bool
    fitness int
}

Answer 1

所以基本上 goroutine 不应该返回一个值，而是将它插入一个 channel 。如果你想等待所有 goroutines 完成，你可以只计算 goroutines 的数量，或者使用 WaitGroup。在这个例子中，这是一个矫枉过正，因为大小是已知的，但无论如何这是一个很好的做法。这是一个修改后的例子:

package main

import (
    "math/rand"
    "sync"
)

type Individual struct {
    gene    []bool
    fitness int
}


func createPopulation(populationSize int, individualSize int) []Individual  {

    // we create a slice with a capacity of populationSize but 0 size
    // so we'll avoid extra unneeded allocations
    population := make([]Individual, 0, populationSize)

    // we create a buffered channel so writing to it won't block while we wait for the waitgroup to finish
    ch := make(chan Individual, populationSize)

    // we create a waitgroup - basically block until N tasks say they are done
    wg := sync.WaitGroup{}

    for i := 0; i < populationSize; i++ {

        //we add 1 to the wait group - each worker will decrease it back
        wg.Add(1)

        //now we spawn a goroutine
        go createIndividual(individualSize, ch, &wg)
    }

    // now we wait for everyone to finish - again, not a must.
    // you can just receive from the channel N times, and use a timeout or something for safety
    wg.Wait()

    // we need to close the channel or the following loop will get stuck
    close(ch)

    // we iterate over the closed channel and receive all data from it
    for individual := range ch {

        population = append(population, individual)
    }
    return population

}   

func createIndividual(size int, ch chan Individual, wg *sync.WaitGroup) {

    var individual = Individual{make([]bool, size), 0}

    for i := 0; i < len(individual.gene); i++ {
        if rand.Intn(2)%2 == 1 {
            individual.gene[i] = true
        } else {
            individual.gene[i] = false
        }
    }

    // push the population object down the channel
    ch <- individual
    // let the wait group know we finished
    wg.Done()

}