当我尝试模拟扇入时陷入僵局 - 使用阶乘计算扇出答案

【问题标题】：Getting deadlock as I try to emulate fan in - fan out with factorial calculations当我尝试模拟扇入时陷入僵局 - 使用阶乘计算扇出
【发布时间】：2018-03-12 15:05:47
【问题描述】：

我正在尝试带有阶乘问题的 fan in - fan out 模式。但我得到：

fatal error: all goroutines are asleep - deadlock!

并且无法确定死锁的原因。

我正在尝试使用扇入扇出模式同时计算 100 个数字的阶乘。

package main

import (
    "fmt"
)

func main() {
    _inChannel := _inListener(generator())
    for val := range _inChannel {
        fmt.Print(val, " -- ")
    }
}

func generator() chan int { // NEED TO CALCULATE FACTORIAL FOR 100 NUMBERS
    ch := make(chan int) // CREATE CHANNEL TO INPUT NUMBERS

    go func() {
        for i := 1; i <= 100; i++ {
            ch <- i
        }
        close(ch) // CLOSE CHANNEL WHEN ALL NUMBERS HAVE BEEN WRITTEM
    }()

    return ch
}

func _inListener(ch chan int) chan int {
    rec := make(chan int) // CHANNEL RECEIVED FROM GENERATOR
    go func() {
        for num := range ch { // RECEIVE THE INPUT NUMBERS FROM GENERATOR
            result := factorial(num) // RESULT IS A NEW CHANNEL CREATED
            rec <- <-result // MERGE INTO A SINGLE CHANNEL; rec
            close(result)
        }
        close(rec)
    }()
    return rec // RETURN THE DEDICATED CHANNEL TO RECEIVE ALL OUTPUTS
}

func factorial(n int) chan int {
    ch := make(chan int) // MAKE A NEW CHANNEL TO OUTPUT THE RESULT 
    // OF FACTORIAL
    total := 1
    for i := n; i > 0; i-- {
        total *= i
    }
    ch <- total
    return ch // RETURN THE CHANNEL HAVING THE FACTORIAL CALCULATED
}

我已经放入了cmets，这样更容易看代码。

【问题讨论】：

标签： go concurrency deadlock channel

【解决方案1】：

我不是渠道专家。我已经开始尝试并更熟悉 go。另一个问题是 int 不够大，无法将所有阶乘超过 20 左右。如您所见，我在生成器函数中添加了一个延迟关闭以及一个名为 done 的逻辑通道。其余的更改可能不需要。对于通道，您需要确保当您将某些内容放在通道上时，某些内容已准备好在通道上取得价值。否则死锁。另外，使用

运行 -race main.go

至少有助于查看哪些线路引起了问题。

我希望这会有所帮助，并且不会因为离题而被删除。

我可以通过这样做来消除死锁：

package main

import (
    "fmt"
)

func main() {
    _gen := generator()
    _inChannel := _inListener(_gen)
    for val := range _inChannel {
        fmt.Print(val, " -- \n")
    }
}

func generator() chan int { // NEED TO CALCULATE FACTORIAL FOR 100 NUMBERS
    ch := make(chan int) // CREATE CHANNEL TO INPUT NUMBERS
    done := make(chan bool)
    go func() {
        defer close(ch)
        for i := 1; i <= 100; i++ {
            ch <- i
        }
        //close(ch) // CLOSE CHANNEL WHEN ALL NUMBERS HAVE BEEN WRITTEM
        done <- true
    }()

    // this function will pull off the done for each function call above.
    go func() {
        for i := 1; i < 100; i++ {
            <-done
        }
    }()

    return ch
}

func _inListener(ch chan int) chan int {
    rec := make(chan int) // CHANNEL RECEIVED FROM GENERATOR
    go func() {
        for num := range ch { // RECEIVE THE INPUT NUMBERS FROM GENERATOR
            result := factorial(num) // RESULT IS A NEW CHANNEL CREATED
            rec <- result            // MERGE INTO A SINGLE CHANNEL; rec
        }
        close(rec)
    }()

    return rec // RETURN THE DEDICATED CHANNEL TO RECEIVE ALL OUTPUTS
}

func factorial(n int) int {
    // OF FACTORIAL
    total := 1
    for i := n; i > 0; i-- {
        total *= i
    }
    return total // RETURN THE CHANNEL HAVING THE FACTORIAL CALCULATED
}

【讨论】：