Question

我不太确定这里发生了什么，因此很难一概而论，但是我会尽力而为。

在几年前的一段视频中，马特·帕克（Matt Parker）敢于让观众发现2的幂，其中不包含任何2的幂的数字。（例如2 ^ 16 =65536。这些数字分别都不是2的幂）。最近，我开始学习Go语言，我认为这是一个很好的入门练习，可以习惯该语言。

我很快创建了它，然后我决定尝试使其并发以充分利用我的四核处理器。这是下坡的地方。

这里的目标是运行恒定数量的goroutine，每个goroutine处理不同数量的数字。我是这样实现程序的：

package main

import (
    "log"
    "math/big"
    "runtime"
)

//The maximum amount of goroutines
const routineAmt int = 3

//The amount of numbers for each routine to check
const rangeSize int64 = 5000

//The current start of the range to start checking
var rangeIndex int64 = 0

func main() {
    //loop forever
    for {
        //if we have less routines running than the maximum
        if runtime.NumGoroutine() < routineAmt {
            c := make(chan bool)
            // start a new one to check the next range:
            go checkRange(rangeIndex, rangeIndex+rangeSize, c)
            // wait for the signal that the values have been copied to the function, so that we can increment them safely:
            <-c
            close(c)
            // increment the rangeIndex for the next routine which will start:
            rangeIndex += rangeSize
        }
    }
}

// Function to check a range of powers of two, whether they contain any power-of-two-digits
func checkRange(from, to int64, c chan bool) {
    c <- true // signal to the main routine that the parameter values have been copied

    // Loop through the range for powers of two, which do not contain any power-of-two-digits
    for i := from; i < to; i++ {
        num := big.NewInt(2)
        num.Exp(num, big.NewInt(i), nil)
        if !hasStringPowerOfTwo(num.String()) {
            log.Println("Found 2 ^", i)
        }
    }
    log.Printf("Checked range %d-%d\n", from, to)
}

// Function to check if a string contains any number which is a power of two
func hasStringPowerOfTwo(input string) bool {
    powersOfTwo := [4]rune{'1', '2', '4', '8'}
    for _, char := range input {
        if runeInArray(char, powersOfTwo) {
            return true
        }
    }
    return false
}

// Function to check if a list of runes contains a certain rune
func runeInArray(a rune, list [4]rune) bool {
    for _, b := range list {
        if b == a {
            return true
        }
    }
    return false
}

等待大约15分钟后，该程序仍然没有完成一个go例程（也就是说，我在控制台中没有看到log.Printf("Checked range %d-%d\n", from, to)）

我尝试将范围大小减小到5，这导致完成一些goroutine，但突然停在2840-2845范围。我以为这可能是因为数字越来越大，计算花费了更多时间，但这没有意义，因为止损很突然。如果是这种情况，我希望经济放缓至少会是逐渐的。

Answer 1

在检查runtime.NumGoroutine时，请勿使用for循环来确保没有太多例程在运行，因为该循环将阻止goruntime正确安排例程，这会降低整件事情。

相反，您应该使用一个缓冲通道，该通道在例程执行完毕后发出信号，以便您可以开始一个新的例程。

我已经调整了您的main功能和checkRange功能：

func main() {
        var done = make(chan struct{}, routineAmt)
        //loop forever
        for i := 0; i < routineAmt; i++ {
                // start a new one to check the next range:
                go checkRange(done, rangeIndex, rangeIndex+rangeSize)
                // increment the rangeIndex for the next routine which will start:
                rangeIndex += rangeSize
        }

        for range done {
                // start a new one to check the next range:
                go checkRange(done, rangeIndex, rangeIndex+rangeSize)
                // increment the rangeIndex for the next routine which will start:
                rangeIndex += rangeSize
        }
}

// Function to check a range of powers of two, whether they contain any power-of-two-digits
func checkRange(done chan<- struct{}, from, to int64) {
        // Loop through the range for powers of two, which do not contain any power-of-two-digits
        for i := from; i < to; i++ {
                num := big.NewInt(2)
                num.Exp(num, big.NewInt(i), nil)
                if !hasStringPowerOfTwo(num.String()) {
                        log.Println("Found 2 ^", i)
                }
        }
        log.Printf("Checked range %d-%d\n", from, to)

        // let our main go routine know we're done with this one
        done <- struct{}{}
}

运行恒定数量的goroutines

1 个答案: