go实例之线程池

　　go语言使用goroutines和channel实现一个工作池相当简单。使用goroutines开指定书目线程，通道分别传递任务和任务结果。简单的线程池代码如下：

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++ {
        <-results
    }
}

　　执行上面代码，将得到以下输出结果

worker 3 started  job 2
worker 1 started  job 1
worker 2 started  job 3
worker 3 finished job 2
worker 3 started  job 4
worker 1 finished job 1
worker 1 started  job 5
worker 2 finished job 3
worker 3 finished job 4
worker 1 finished job 5

　　看代码中注释也大概能理解每一步的含义，代码25行和26行分别初始化了2个通道，用于发送任务给子线程和接收子线程计算的任务结果。30-32行代码是启动了3个子线程，用于处理任务，并将任务通道和结果通道传递给了线程函数。36-38行代码是发送任务到jobs通道，工作线程在没有任务时，是阻塞着等待任务，当发现任务通道中有任务时，开始执行任务，当任务执行完毕时，将任务结果发送给结果通道。

　　jobs <-chan int：只能接收数据

　　results chan<- int：只能发送数据

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奋斗中的无名小卒。。。