英文:
Saving results from a parallelized goroutine
问题
我正在尝试在Go语言中并行化一个操作，并以一种可以迭代求和的方式保存结果。
我已经成功设置了参数，以确保没有死锁发生，并且我已经确认操作在函数内部正确地工作和保存。但是，当我迭代我的结构体切片并尝试求和操作的结果时，它们都保持为0。我尝试过通过引用、指针和通道（导致死锁）传递参数。
我只找到了这个例子来帮助：https://golang.org/doc/effective_go.html#parallel。但是这个例子似乎已经过时了，因为Vector已经被弃用了？我也没有找到任何关于这个函数（在例子中）是如何构造的参考（在名称之前使用func (u Vector)）。我尝试用切片替换它，但是得到了编译时错误。
任何帮助将不胜感激。这是我代码的关键部分：
type job struct {
a int
b int
result *big.Int
}
func choose(jobs []Job, c chan int) {
temp := new(big.Int)
for _,job := range jobs {
job.result = //在job.a和job.b上执行操作
//fmt.Println(job.result)
}
c <- 1
}
func main() {
num := 100 //可以非常大（所以我们需要big.Int）
n := num
k := 0
const numCPU = 6 //runtime.NumCPU
count := new(big.Int)
// 创建一个二维切片的作业，每个核心一个
jobs := make([][]Job, numCPU)
for (float64(k) <= math.Ceil(float64(num / 2))) {
// 每个核心添加一个作业，交替进行，以便
// 作业集在难度上相似
for i := 0; i < numCPU; i++ {
if !(float64(k) <= math.Ceil(float64(num / 2))) {
break
}
jobs[i] = append(jobs[i], Job{n, k, new(big.Int)})
n -= 1
k += 1
}
}
c := make(chan int, numCPU)
for i := 0; i < numCPU; i++ {
go choose(jobs[i], c)
}
// 清空通道
for i := 0; i < numCPU; i++ {
<-c
}
// 计算完成
for i := range jobs {
for _,job := range jobs[i] {
//fmt.Println(job.result)
count.Add(count, job.result)
}
}
fmt.Println(count)
}
这是在Go Playground上运行的代码：https://play.golang.org/p/X5IYaG36U-
英文:
I am trying to parallelize an operation in golang and save the results in a manner that I can iterate over to sum up afterwords.
I have managed to set up the parameters so that no deadlock occurs, and I have confirmed that the operations are working and being saved correctly within the function. When I iterate over the Slice of my struct and try and sum up the results of the operation, they all remain 0. I have tried passing by reference, with pointers, and with channels (causes deadlock).
I have only found this example for help: https://golang.org/doc/effective_go.html#parallel. But this seems outdated now, as Vector as been deprecated? I also have not found any references to the way this function (in the example) was constructed (with the func (u Vector) before the name). I tried replacing this with a Slice but got compile time errors.
Any help would be very appreciated. Here is the key parts of my code:
type job struct {
a int
b int
result *big.Int
}
func choose(jobs []Job, c chan int) {
temp := new(big.Int)
for _,job := range jobs {
job.result = //perform operation on job.a and job.b
//fmt.Println(job.result)
}
c <- 1
}
func main() {
num := 100 //can be very large (why we need big.Int)
n := num
k := 0
const numCPU = 6 //runtime.NumCPU
count := new(big.Int)
// create a 2d slice of jobs, one for each core
jobs := make([][]Job, numCPU)
for (float64(k) <= math.Ceil(float64(num / 2))) {
// add one job to each core, alternating so that
// job set is similar in difficulty
for i := 0; i < numCPU; i++ {
if !(float64(k) <= math.Ceil(float64(num / 2))) {
break
}
jobs[i] = append(jobs[i], Job{n, k, new(big.Int)})
n -= 1
k += 1
}
}
c := make(chan int, numCPU)
for i := 0; i < numCPU; i++ {
go choose(jobs[i], c)
}
// drain the channel
for i := 0; i < numCPU; i++ {
<-c
}
// computations are done
for i := range jobs {
for _,job := range jobs[i] {
//fmt.Println(job.result)
count.Add(count, job.result)
}
}
fmt.Println(count)
}
Here is the code running on the go playground https://play.golang.org/p/X5IYaG36U-
答案1
得分: 2
只要[]Job切片一次只被一个goroutine修改，就没有理由不能直接修改作业。
for i, job := range jobs {
jobs[i].result = temp.Binomial(int64(job.a), int64(job.b))
}
https://play.golang.org/p/CcEGsa1fLh
你还应该使用WaitGroup，而不是依赖于自己在通道中计数令牌。
英文:
As long as the []Job slice is only modified by one goroutine at a time, there's no reason you can't modify the job in place.
for i, job := range jobs {
jobs[i].result = temp.Binomial(int64(job.a), int64(job.b))
}
https://play.golang.org/p/CcEGsa1fLh
You should also use a WaitGroup, rather than rely on counting tokens in a channel yourself.
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