Kotlin Coroutines文档中的质数示例如何工作？

Question

我正在阅读Kotlin的协程文档，并且在完成本示例之前一直很好。我很难理解它在找到质数时如何进行计算，特别是如何返回filter函数的返回值并将其分配给cur，以及如何从numbersFrom方法中生成数字。

我添加了调试语句来尝试跟踪正在运行的各种协程，但是当启动新协程并从其他协程接收编号时，我仍然迷失在逻辑流程上。

https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md#prime-numbers-with-pipeline

代码：

fun log(msg: String) = println("[${Thread.currentThread().name}] $msg")

fun main(args: Array<String>) = runBlocking<Unit> {
    var cur = numbersFrom(context, 2)
    for (i in 1..10) {
        val prime = cur.receive()
        println(prime)
        cur = filter(context, cur, prime)
    }
}

fun numbersFrom(context: CoroutineContext, start: Int) = produce<Int>(context) {
       var x = start
    while (true) {
        log("NumbersFrom Send: ${x}")
        send(x++)
    } // infinite stream of integers from start
}

fun filter(context: CoroutineContext, numbers: ReceiveChannel<Int>, prime: Int) = produce<Int>(context) {
    for (x in numbers) {
        log("filter ${x}, prime ${prime}")
        if (x % prime != 0) {
            send(x)
        }
    }
}

外出：

[main @coroutine#2] NumbersFrom Send: 2
[main @coroutine#2] NumbersFrom Send: 3
2
[main @coroutine#3] filter 3, prime 2
[main @coroutine#2] NumbersFrom Send: 4
[main @coroutine#2] NumbersFrom Send: 5
3
[main @coroutine#3] filter 4, prime 2
[main @coroutine#3] filter 5, prime 2
[main @coroutine#4] filter 5, prime 3
[main @coroutine#2] NumbersFrom Send: 6
[main @coroutine#3] filter 6, prime 2
5
[main @coroutine#2] NumbersFrom Send: 7
[main @coroutine#2] NumbersFrom Send: 8
[main @coroutine#3] filter 7, prime 2
[main @coroutine#3] filter 8, prime 2
[main @coroutine#4] filter 7, prime 3
[main @coroutine#2] NumbersFrom Send: 9
[main @coroutine#2] NumbersFrom Send: 10
[main @coroutine#5] filter 7, prime 5
[main @coroutine#3] filter 9, prime 2
[main @coroutine#3] filter 10, prime 2
7
[main @coroutine#4] filter 9, prime 3
[main @coroutine#2] NumbersFrom Send: 11
[main @coroutine#2] NumbersFrom Send: 12
[main @coroutine#3] filter 11, prime 2
[main @coroutine#3] filter 12, prime 2
[main @coroutine#4] filter 11, prime 3
[main @coroutine#2] NumbersFrom Send: 13
[main @coroutine#2] NumbersFrom Send: 14
[main @coroutine#5] filter 11, prime 5
[main @coroutine#3] filter 13, prime 2
[main @coroutine#3] filter 14, prime 2
[main @coroutine#6] filter 11, prime 7
[main @coroutine#4] filter 13, prime 3
[main @coroutine#2] NumbersFrom Send: 15
[main @coroutine#2] NumbersFrom Send: 16
11
[main @coroutine#5] filter 13, prime 5
[main @coroutine#3] filter 15, prime 2
[main @coroutine#3] filter 16, prime 2
[main @coroutine#6] filter 13, prime 7
[main @coroutine#4] filter 15, prime 3
[main @coroutine#2] NumbersFrom Send: 17
[main @coroutine#2] NumbersFrom Send: 18
[main @coroutine#7] filter 13, prime 11
[main @coroutine#3] filter 17, prime 2
[main @coroutine#3] filter 18, prime 2
13
[main @coroutine#4] filter 17, prime 3
[main @coroutine#2] NumbersFrom Send: 19
[main @coroutine#2] NumbersFrom Send: 20
[main @coroutine#5] filter 17, prime 5
[main @coroutine#3] filter 19, prime 2
[main @coroutine#3] filter 20, prime 2
[main @coroutine#6] filter 17, prime 7
[main @coroutine#4] filter 19, prime 3
[main @coroutine#2] NumbersFrom Send: 21
[main @coroutine#2] NumbersFrom Send: 22
[main @coroutine#7] filter 17, prime 11
[main @coroutine#5] filter 19, prime 5
[main @coroutine#3] filter 21, prime 2
[main @coroutine#3] filter 22, prime 2
[main @coroutine#8] filter 17, prime 13
[main @coroutine#6] filter 19, prime 7
[main @coroutine#4] filter 21, prime 3
[main @coroutine#2] NumbersFrom Send: 23
[main @coroutine#2] NumbersFrom Send: 24
17
[main @coroutine#7] filter 19, prime 11
[main @coroutine#3] filter 23, prime 2
[main @coroutine#3] filter 24, prime 2
[main @coroutine#8] filter 19, prime 13
[main @coroutine#4] filter 23, prime 3
[main @coroutine#2] NumbersFrom Send: 25
[main @coroutine#2] NumbersFrom Send: 26
[main @coroutine#9] filter 19, prime 17
[main @coroutine#5] filter 23, prime 5
[main @coroutine#3] filter 25, prime 2
[main @coroutine#3] filter 26, prime 2
19
[main @coroutine#6] filter 23, prime 7
[main @coroutine#4] filter 25, prime 3
[main @coroutine#2] NumbersFrom Send: 27
[main @coroutine#2] NumbersFrom Send: 28
[main @coroutine#7] filter 23, prime 11
[main @coroutine#5] filter 25, prime 5
[main @coroutine#3] filter 27, prime 2
[main @coroutine#3] filter 28, prime 2
[main @coroutine#8] filter 23, prime 13
[main @coroutine#4] filter 27, prime 3
[main @coroutine#2] NumbersFrom Send: 29
[main @coroutine#2] NumbersFrom Send: 30
[main @coroutine#9] filter 23, prime 17
[main @coroutine#3] filter 29, prime 2
[main @coroutine#3] filter 30, prime 2
[main @coroutine#10] filter 23, prime 19
[main @coroutine#4] filter 29, prime 3
[main @coroutine#2] NumbersFrom Send: 31
[main @coroutine#2] NumbersFrom Send: 32
23
[main @coroutine#5] filter 29, prime 5
[main @coroutine#3] filter 31, prime 2
[main @coroutine#3] filter 32, prime 2
[main @coroutine#6] filter 29, prime 7
[main @coroutine#4] filter 31, prime 3
[main @coroutine#2] NumbersFrom Send: 33
[main @coroutine#2] NumbersFrom Send: 34
[main @coroutine#7] filter 29, prime 11
[main @coroutine#5] filter 31, prime 5
[main @coroutine#3] filter 33, prime 2
[main @coroutine#3] filter 34, prime 2
[main @coroutine#8] filter 29, prime 13
[main @coroutine#6] filter 31, prime 7
[main @coroutine#4] filter 33, prime 3
[main @coroutine#2] NumbersFrom Send: 35
[main @coroutine#2] NumbersFrom Send: 36
[main @coroutine#9] filter 29, prime 17
[main @coroutine#7] filter 31, prime 11
[main @coroutine#3] filter 35, prime 2
[main @coroutine#3] filter 36, prime 2
[main @coroutine#10] filter 29, prime 19
[main @coroutine#8] filter 31, prime 13
[main @coroutine#4] filter 35, prime 3
[main @coroutine#2] NumbersFrom Send: 37
[main @coroutine#2] NumbersFrom Send: 38
[main @coroutine#11] filter 29, prime 23
[main @coroutine#9] filter 31, prime 17
[main @coroutine#5] filter 35, prime 5
[main @coroutine#3] filter 37, prime 2
[main @coroutine#3] filter 38, prime 2
29
[main @coroutine#10] filter 31, prime 19
[main @coroutine#4] filter 37, prime 3
[main @coroutine#2] NumbersFrom Send: 39

Answer 1

该示例的重点是实现Eratosthenes筛。换句话说，通过滤除因数不可分的质数来查找质数。剩下的一切都是素数。

让我们看看我们有什么。现在，我将忽略所有context变量，这只会使事情更容易谈论。

首先，我们有一个名为的函数numbersFrom，它只是从2开始的无穷整数序列（在这种情况下）。

我们还有filter一个名为的函数，它接收一个通道，以及一个可能是质数的数字。查看返回类型，我们可以看到该函数返回了一个新的生产者。为了产生结果（Int在本例中为s），send可以调用该函数。查看函数的主体，filter将接受通道外的数字（通过send），并拒绝可被质数整除的任何内容（不执行任何操作）。

例如，如果通道产生4，而素数是2，则拒绝。另一方面，如果通道产生5，质数为2，则send该数字也会随之增加。现在应该很明显地filter做到了它的名字所说的-读取输入，找到喜欢的输入，并将它们发送到输出。

现在让我们看一下主要功能。首先，我们创建一个从2开始的数字流（巧合，第一个质数！），并将其分配给cur。到目前为止，一切都很好。

接下来，我们开始循环。我将10减为3，以使事情更容易理解，但从本质上讲，该数字表示主要方法将计算多少个素数。如果要使用前100个素数，请将其设置为100。

在循环中，我们采取的第一个数字关闭号码列表，通过调用receive()上cur。这是一个暂停功能。而且如上所述，它的第一个prime值将为2 。

现在这是有趣的部分。我们2以此为基础，并将其作为对filter以及cur当前当前的Ints 流的调用的基础，然后将其重新分配给cur。那是什么意思呢？cur现在表示一个整数流，过滤后不能被2整除！

在下一个循环中，我们从cur通道中取出第一个数字，它是3。下一个质数。为什么是3？因为filter(2)允许它通过（3％2！= 0）。这是有趣的部分。现在我们获取cur（一个不能被2整除的数字过滤列表），并将其filter与3（我们最近的质数）一起传递给函数。现在cur表示不被2或3整除的数字流。

从本质上来说，我们有以下几点：

numbers -> filter(2) -> filter(3)

或者，再读一遍（不太精确的wrt协程，但是更容易描绘）：

filter(3, filter(2, numbers))

使其成为开头的任何数字cur都是质数，因为它通过了所有过滤器。

感谢您提出这个问题！“ 去学习Kotlin Coroutines ”已经在我的研究列表上呆了几周，我早上好阅读有关它们的信息，并弄清楚了这一点。