英文:
Does a goroutine necessarily run on a different CPU?
问题
以下是翻译好的内容：
以下摘录来自https://go.dev/doc/effective_go#parallel。
我们在循环中独立地启动这些片段，每个CPU一个。它们可以以任何顺序完成，但这并不重要；我们只需在启动所有goroutine后通过从通道中读取来计算完成信号。
const numCPU = 4 // CPU核心数
func (v Vector) DoAll(u Vector) {
c := make(chan int, numCPU) // 缓冲区大小可选，但是合理。
for i := 0; i < numCPU; i++ {
go v.DoSome(i*len(v)/numCPU, (i+1)*len(v)/numCPU, u, c)
}
// 清空通道。
for i := 0; i < numCPU; i++ {
<-c // 等待一个任务完成
}
// 全部完成。
}
为什么文章中指定了"每个CPU一个"？多个goroutine不需要在不同的CPU上执行。实际上，子节的最后一段提醒读者并不要混淆并发(concurrency)和并行(parallelism)的概念：
请确保不要混淆并发(concurrency)——将程序结构化为独立执行的组件——和并行(parallelism)——在多个CPU上为了效率而并行执行计算。
英文:
The following excerpt is from https://go.dev/doc/effective_go#parallel.
> We launch the pieces independently in a loop, one per CPU. They can complete in any order but it doesn't matter; we just count the completion signals by draining the channel after launching all the goroutines.
const numCPU = 4 // number of CPU cores
func (v Vector) DoAll(u Vector) {
c := make(chan int, numCPU) // Buffering optional but sensible.
for i := 0; i < numCPU; i++ {
go v.DoSome(i*len(v)/numCPU, (i+1)*len(v)/numCPU, u, c)
}
// Drain the channel.
for i := 0; i < numCPU; i++ {
<-c // wait for one task to complete
}
// All done.
}
Why does the article specify "one per CPU"? Multiple goroutines need not be executed on different CPUs. In fact, the last paragraph in the sub-section reminds the reader that concurrency is not parallelism:
> Be sure not to confuse the ideas of concurrency—structuring a program as independently executing components—and parallelism—executing calculations in parallel for efficiency on multiple CPUs.
答案1
得分: 2
一个 goroutine 是否一定在不同的 CPU 上运行？
不一定，但可能会。
这里没有什么特别的。
为什么文章中指定“每个 CPU 一个”？
它本可以说 5 或者 2。实际上这里没有任何重要的隐藏信息。这只是一个例子，而不是 goroutine 调度的规范。
英文:
> Does a goroutine necessarily run on a different CPU?
No, but it might.
Nothing to see here.
> why the article specifies "one per CPU"
It could have said 5 or 2. Really there is nothing of importance hidden here. This is just an example, not the specification of goroutine scheduling.
答案2
得分: 0
为什么文章要指定“每个CPU一个”？多个goroutine不需要在不同的CPU上执行。实际上，子节的最后一段提醒读者并发不等于并行。
goroutine与操作系统线程（M：N）映射，并且每个goroutine一次只能使用一个线程，但无法预测它是否使用一个CPU来执行所有4个（GOMAXPROCS）goroutine，或者使用2个CPU、3个CPU或所有4个CPU。这取决于许多因素，而所有这些复杂性都被Go运行时隐藏起来。
英文:
> Why does the article specify "one per CPU"? Multiple goroutines need
> not be executed on different CPUs. In fact, the last paragraph in the
> sub-section reminds the reader that concurrency is not parallelism:
goroutines are mapped with OS threads (M:N) and each goroutine can use a maximum of one thread at a time but you can not predict whether it is using the 1 CPU to execute all the 4 (GOMAXPROCS) goutines or it is use 2 cpu or 3 cpu or all 4 cpu.It is depending upon many factor's and all these complexity is hidden by go runtime
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