运行恒定数量的goroutines

Question

我不完全确定这里发生了什么，所以很难概括我的问题，但我会尽力而为。

在几年前的视频中，马特帕克敢于让他的观众发现两个力量，它不包含任何数字，这是2的幂。 （例如，2 ^ 16 = 65536.这些数字中没有一个是2的幂）。最近我开始学习Go，我认为习惯这门语言会是一个很好的入门练习。

我很快就创建了这个，然后我决定尝试将它同时用来充分利用我的四核处理器。事情发生了变化。

这里的目标是运行恒定数量的goroutine，每个goroutine处理不同批次的数字。我实现了这样的程序：

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
}

等了大约15分钟左右后，程序仍然没有完成一个单独的程序（也就是说，我没有在控制台中看到log.Printf("Checked range %d-%d\n", from, to)）

我尝试将范围大小降低到5，这导致几个goroutine完成但它突然停在2840-2845范围内。我认为这可能是由于数字越来越大而且计算花费的时间越来越多，但这并不合理，因为止损是非常突然的。如果是这种情况，我预计减速至少会逐渐减缓。

Answer 1

你不应该使用带有runtime.NumGoroutine检查的for循环来确保没有太多的例程在运行，因为循环会阻止goruntime正确安排你的例程，它会减慢整个过程。

相反，您应该使用缓冲通道，该通道在例程完成时发出信号，以便您可以开始新的通道。

我调整了你的main函数和checkRange函数：

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{}{}
}