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【转】Go by Example: Worker Pools

原文:https://gobyexample.com/worker-pools

Our running program shows the 5 jobs being executed by various workers. The program only takes about 2 seconds despite doing about 5 seconds of total work because there are 3 workers operating concurrently.

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package main
 
import (
    "fmt"
    "time"
)
 
func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "started  job", j)
        time.Sleep(time.Second)
        fmt.Println("worker", id, "finished job", j)
        results <- j * 2
    }
}
 
func main() {
 
    const numJobs = 5
    jobs := make(chan int, numJobs)
    results := make(chan int, numJobs)
 
    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }
 
    for j := 1; j <= numJobs; j++ {
        jobs <- j
    }
    close(jobs)
 
    for a := 1; a <= numJobs; a++ {
        <-results
    }
}

  

下面这个版本为什么会死锁呢??

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package main
 
import "fmt"
import "time"
 
// Here's the worker, of which we'll run several
// concurrent instances. These workers will receive
// work on the `jobs` channel and send the corresponding
// results on `results`. We'll sleep a second per job to
// simulate an expensive task.
func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "started  job", j)
        time.Sleep(time.Second)
        fmt.Println("worker", id, "finished job", j)
        results <- j * 2
    }
}
 
func main() {
 
    // In order to use our pool of workers we need to send
    // them work and collect their results. We make 2
    // channels for this.
    jobs := make(chan int, 100)
    results := make(chan int, 100)
 
    // This starts up 3 workers, initially blocked
    // because there are no jobs yet.
    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }
 
    // Here we send 5 `jobs` and then `close` that
    // channel to indicate that's all the work we have.
    for j := 1; j <= 5; j++ {
        jobs <- j
    }
    close(jobs)
 
    // Finally we collect all the results of the work.
    //for a := 1; a <= 5; a++ {
    //   fmt.Println( <-results)
    //}
    for v := range results {
      fmt.Println(v)
    }
}

  

 

 

 

 

——————————————————————————————————————————————————————————

 

In this example we’ll look at how to implement a worker pool using goroutines and channels.

 
 
package main
 
import (
    "fmt"
    "time"
)

Here’s the worker, of which we’ll run several concurrent instances. These workers will receive work on the jobschannel and send the corresponding results on results. We’ll sleep a second per job to simulate an expensive task.

func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "started  job", j)
        time.Sleep(time.Second)
        fmt.Println("worker", id, "finished job", j)
        results <- j * 2
    }
}
 
func main() {

In order to use our pool of workers we need to send them work and collect their results. We make 2 channels for this.

    const numJobs = 5
    jobs := make(chan int, numJobs)
    results := make(chan int, numJobs)

This starts up 3 workers, initially blocked because there are no jobs yet.

    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }

Here we send 5 jobs and then close that channel to indicate that’s all the work we have.

    for j := 1; j <= numJobs; j++ {
        jobs <- j
    }
    close(jobs)

Finally we collect all the results of the work. This also ensures that the worker goroutines have finished. An alternative way to wait for multiple goroutines is to use a WaitGroup.

    for a := 1; a <= numJobs; a++ {
        <-results
    }
}

Our running program shows the 5 jobs being executed by various workers. The program only takes about 2 seconds despite doing about 5 seconds of total work because there are 3 workers operating concurrently.

posted @   立志做一个好的程序员  阅读(137)  评论(0编辑  收藏  举报
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