尝试编写工作方法池时出现死锁
在下面的代码中，我不明白为什么“Worker”方法似乎退出而不是从输入通道“in”中提取值并处理它们。
我曾假设他们只会在消耗来自输入通道“in”的所有输入并处理它们之后才会返回
package main
import (
"fmt"
"sync"
)
type ParallelCallback func(chan int, chan Result, int, *sync.WaitGroup)
type Result struct {
i int
val int
}
func Worker(in chan int, out chan Result, id int, wg *sync.WaitGroup) {
for item := range in {
item *= item // returns the square of the input value
fmt.Printf("=> %d: %d\n", id, item)
out <- Result{item, id}
}
wg.Done()
fmt.Printf("%d exiting ", id)
}
func Run_parallel(n_workers int, in chan int, out chan Result, Worker ParallelCallback) {
wg := sync.WaitGroup{}
for id := 0; id < n_workers; id++ {
fmt.Printf("Starting : %d\n", id)
wg.Add(1)
go Worker(in, out, id, &wg)
}
wg.Wait() // wait for all workers to complete their tasks
close(out) // close the output channel when all tasks are completed
}
const (
NW = 4
)
func main() {
in := make(chan int)
out := make(chan Result)
go func() {
for i := 0; i < 100; i++ {
in <- i
}
close(in)
}()
Run_parallel(NW, in, out, Worker)
for item := range out {
fmt.Printf("From out : %d: %d", item.i, item.val)
}
}
输出是
Starting : 0
Starting : 1
Starting : 2
Starting : 3
=> 3: 0
=> 0: 1
=> 1: 4
=> 2: 9
fatal error: all goroutines are asleep - deadlock!
慕森卡3回答
-
繁华开满天机
致命错误：所有 goroutine 都处于休眠状态 - 死锁！完整的错误显示了每个 goroutine “卡住”的位置。 如果你在操场上运行它，它甚至会显示你的行号。这让我很容易诊断。您Run_parallel在maingroutine 中运行，因此在main可以读取之前out，Run_parallel必须返回。在Run_parallel可以返回之前，它必须wg.Wait()。但在工人打电话之前wg.Done()，他们必须写信给out。这就是导致僵局的原因。一种解决方案很简单：只需Run_parallel在自己的 Goroutine 中并发运行。 go Run_parallel(NW, in, out, Worker)现在，mainrange over out，等待outs 关闭以发出完成信号。 Run_parallel等待工人与wg.Wait()，工人将范围内in。所有的工作都会完成，并且在完成之前程序不会结束。（https://go.dev/play/p/oMrgH2U09tQ） -
暮色呼如
解决方案 ：Run_parallel 必须在它自己的 goroutine 中运行：package mainimport ( "fmt" "sync")type ParallelCallback func(chan int, chan Result, int, *sync.WaitGroup)type Result struct { id int val int}func Worker(in chan int, out chan Result, id int, wg *sync.WaitGroup) { defer wg.Done() for item := range in { item *= 2 // returns the double of the input value (Bogus handling of data) out <- Result{id, item} }}func Run_parallel(n_workers int, in chan int, out chan Result, Worker ParallelCallback) { wg := sync.WaitGroup{} for id := 0; id < n_workers; id++ { wg.Add(1) go Worker(in, out, id, &wg) } wg.Wait() // wait for all workers to complete their tasks close(out) // close the output channel when all tasks are completed}const ( NW = 8)func main() { in := make(chan int) out := make(chan Result) go func() { for i := 0; i < 10; i++ { in <- i } close(in) }() go Run_parallel(NW, in, out, Worker) for item := range out { fmt.Printf("From out [%d]: %d\n", item.id, item.val) } println("- - - All done - - -")} -
绝地无双
解决方案的替代配方：在那个替代公式中，没有必要将 Run_parallel 作为 goroutine 启动（它会触发自己的 goroutine）。我更喜欢第二种解决方案，因为它自动执行 Run_parallel() 必须与主函数并行运行的事实。此外，出于同样的原因，它更安全，更不容易出错（无需记住使用 go 关键字运行 Run_parallel）。package mainimport ( "fmt" "sync")type ParallelCallback func(chan int, chan Result, int, *sync.WaitGroup)type Result struct { id int val int}func Worker(in chan int, out chan Result, id int, wg *sync.WaitGroup) { defer wg.Done() for item := range in { item *= 2 // returns the double of the input value (Bogus handling of data) out <- Result{id, item} }}func Run_parallel(n_workers int, in chan int, out chan Result, Worker ParallelCallback) { go func() { wg := sync.WaitGroup{} defer close(out) // close the output channel when all tasks are completed for id := 0; id < n_workers; id++ { wg.Add(1) go Worker(in, out, id, &wg) } wg.Wait() // wait for all workers to complete their tasks *and* trigger the -differed- close(out) }()}const ( NW = 8)func main() { in := make(chan int) out := make(chan Result) go func() { defer close(in) for i := 0; i < 10; i++ { in <- i } }() Run_parallel(NW, in, out, Worker) for item := range out { fmt.Printf("From out [%d]: %d\n", item.id, item.val) } println("- - - All done - - -")}
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