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：

 1 package main
 2 
 3 import "fmt"
 4 import "time"
 5 
 6 // Here's the worker, of which we'll run several
 7 // concurrent instances. These workers will receive
 8 // work on the `jobs` channel and send the corresponding
 9 // results on `results`. We'll sleep a second per job to
10 // simulate an expensive task.
11 func worker(id int, jobs <-chan int, results chan<- int) {
12     for j := range jobs {
13         fmt.Println("worker", id, "started  job", j)
14         time.Sleep(time.Second)
15         fmt.Println("worker", id, "finished job", j)
16         results <- j * 2
17     }
18 }
19 
20 func main() {
21 
22     // In order to use our pool of workers we need to send
23     // them work and collect their results. We make 2
24     // channels for this.
25     jobs := make(chan int, 100)
26     results := make(chan int, 100)
27 
28     // This starts up 3 workers, initially blocked
29     // because there are no jobs yet.
30     for w := 1; w <= 3; w++ {
31         go worker(w, jobs, results)
32     }
33 
34     // Here we send 5 `jobs` and then `close` that
35     // channel to indicate that's all the work we have.
36     for j := 1; j <= 5; j++ {
37         jobs <- j
38     }
39     close(jobs)
40 
41     // Finally we collect all the results of the work.
42     for a := 1; a <= 5; a++ {
43         <-results
44     }
45 }

　　执行上面代码，将得到以下输出结果

 1 worker 3 started  job 2
 2 worker 1 started  job 1
 3 worker 2 started  job 3
 4 worker 3 finished job 2
 5 worker 3 started  job 4
 6 worker 1 finished job 1
 7 worker 1 started  job 5
 8 worker 2 finished job 3
 9 worker 3 finished job 4
10 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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