在现实世界中，经常有一些工作是属于流水线类型的，它们每一个步骤都是紧密关联的，第一步先做什么，再做做么，最后做什么。特别是制造业这个行业，基本全是流水线生产车间。在我们开发中也经常遇到这类的业务场景。
假如我们有个流水线共分三个步骤，分别是 job1、job2和job3。代码：https://play.golang.org/p/e7ZlP9ofXB3
package main
import (
"fmt"
"time"
)
func job1(count int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for i := 0; i < count; i++ {
time.Sleep(time.Second)
fmt.Println("job1 finish:", 1)
outCh <- 1
}
}()
return outCh
}
func job2(inCh <-chan int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for val := range inCh {
// 耗时2秒
time.Sleep(time.Second * 2)
val++
fmt.Println("job2 finish:", val)
outCh <- val
}
}()
return outCh
}
func job3(inCh <-chan int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for val := range inCh {
val++
fmt.Println("job3 finish:", val)
outCh <- val
}
}()
return outCh
}
func main() {
t := time.Now()
firstResult := job1(10)
secondResult := job2(firstResult)
thirdResult := job3(secondResult)
for v := range thirdResult {
fmt.Println(v)
}
fmt.Println("all finish")
fmt.Println("duration:", time.Since(t).String())
}
输出结果为
job1 finish: 1 job1 finish: 1 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job2 finish: 2 job3 finish: 3 3 job2 finish: 2 job3 finish: 3 3 job2 finish: 2 job3 finish: 3 3 all finish duration: 21s
共计计算21秒。主要是因为job2中的耗时太久导致，现在我们的主要任务就是解决掉这个问题了。
这里只用了一个job2来处理job1的结果，如果我们能多开启几个goroutine job2并行处理会不会提升性能呢?
现在我们改进下代码，解决job2耗时的问题，需要注意一下，这里对ch的关闭也要作一下调整，由于启用了多个job2的goroutine，所以在job2内部进行关闭了。代码https://play.golang.org/p/qebQ00v973C
package main
import (
"fmt"
"sync"
"time"
)
func job1(count int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for i := 0; i < count; i++ {
time.Sleep(time.Second)
fmt.Println("job1 finish:", 1)
outCh <- 1
}
}()
return outCh
}
func job2(inCh <-chan int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for val := range inCh {
// 耗时2秒
time.Sleep(time.Second * 2)
val++
fmt.Println("job2 finish:", val)
outCh <- val
}
}()
return outCh
}
func job3(inCh <-chan int) <-chan int {
outCh := make(chan int, 2)
go func() {
defer close(outCh)
for val := range inCh {
val++
fmt.Println("job3 finish:", val)
outCh <- val
}
}()
return outCh
}
func merge(inCh ...<-chan int) <-chan int {
outCh := make(chan int, 2)
var wg sync.WaitGroup
for _, ch := range inCh {
wg.Add(1)
go func(wg *sync.WaitGroup, in <-chan int) {
defer wg.Done()
for val := range in {
outCh <- val
}
}(&wg, ch)
}
// 重要注意，wg.Wait() 一定要在goroutine里运行，否则会引起deadlock
go func() {
wg.Wait()
close(outCh)
}()
return outCh
}
func main() {
t := time.Now()
firstResult := job1(10)
// 拆分成三个job2，即3个goroutine （扇出）
secondResult1 := job2(firstResult)
secondResult2 := job2(firstResult)
secondResult3 := job2(firstResult)
// 合并结果(扇入）
secondResult := merge(secondResult1, secondResult2, secondResult3)
thirdResult := job3(secondResult)
for v := range thirdResult {
fmt.Println(v)
}
fmt.Println("all finish")
fmt.Println("duration:", time.Since(t).String())
}
输出结果
job1 finish: 1 job1 finish: 1 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job1 finish: 1 job2 finish: 2 job3 finish: 3 3 job2 finish: 2 job3 finish: 3 3 job2 finish: 2 job3 finish: 3 3 all finish duration: 12s
可以看到，性能提升了90%，由原来的22s减少到12s。上面代码中为了演示效果，使用的缓冲chan很小，如果调大的话，性能更明显。
FAN-OUT模式：多个goroutine从同一个通道读取数据，直到该通道关闭。OUT是一种张开的模式（1对多），所以又被称为扇出，可以用来分发任务。
FAN-IN模式：1个goroutine从多个通道读取数据，直到这些通道关闭。IN是一种收敛的模式（多对1），所以又被称为扇入，用来收集处理的结果。
是不是很像扇子的状态, 先展开(扇出)再全并(扇入)。
总结：在类似流水线这类的逻辑中，我们可以使用FAN-IN和FAN-OUT模式来提升程序性能。