帶buffer的chan能同步嗎?

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

具體看下面2個例子:

無 buffer 的:
http://play.golang.org/p/RwPbCcueWh

func main() {    ch := make(chan bool)    go func() {        println("fuck buffer channel")        <-ch    }()    ch <- true}

有buffer的:
http://play.golang.org/p/YV9H6WPYuJ

func main() {    ch := make(chan bool, 1)    go func() {        println("fuck buffer channel")        <-ch    }()    ch <- true}

第二個程式(有buffer的chan)無法保證收/發同步, 導致main退出時 println 還未執行.
說明帶buffer的chan是不能保證收/發同步.

下面是一個構造的測試例子
http://play.golang.org/p/vQQCv9nG15

package mainimport (    "fmt"    "sync"    "time")func main() {    testNoBufferChan()    testBufferChan()}func testNoBufferChan() {    wg := new(sync.WaitGroup)    ch := make(chan bool)    wg.Add(1)    go func() {        defer wg.Done()        time.Sleep(10 * time.Second)        fmt.Println(time.Now(), "NoBufferChan recv begin")        <-ch        fmt.Println(time.Now(), "NoBufferChan recv end")    }()    fmt.Println(time.Now(), "NoBufferChan send begin")    ch <- true    fmt.Println(time.Now(), "NoBufferChan send end")    wg.Wait()}func testBufferChan() {    wg := new(sync.WaitGroup)    ch := make(chan bool, 1)    wg.Add(1)    go func() {        defer wg.Done()        time.Sleep(10 * time.Second)        fmt.Println(time.Now(), "BufferChan recv begin")        <-ch        fmt.Println(time.Now(), "BufferChan recv end")    }()    fmt.Println(time.Now(), "BufferChan send begin")    ch <- true    fmt.Println(time.Now(), "BufferChan send end")    wg.Wait()}

在 play 上的結果(play上的是假時間):

2009-11-10 23:00:00 +0000 UTC NoBufferChan send begin2009-11-10 23:00:10 +0000 UTC NoBufferChan recv begin2009-11-10 23:00:10 +0000 UTC NoBufferChan recv end2009-11-10 23:00:10 +0000 UTC NoBufferChan send end2009-11-10 23:00:10 +0000 UTC BufferChan send begin2009-11-10 23:00:10 +0000 UTC BufferChan send end2009-11-10 23:00:20 +0000 UTC BufferChan recv begin2009-11-10 23:00:20 +0000 UTC BufferChan recv end

在本機啟動並執行結果:

2014-05-09 10:41:17.5611304 +0800 CST NoBufferChan send begin2014-05-09 10:41:27.5637025 +0800 CST NoBufferChan recv begin2014-05-09 10:41:27.5637025 +0800 CST NoBufferChan recv end2014-05-09 10:41:27.5637025 +0800 CST NoBufferChan send end2014-05-09 10:41:27.5647026 +0800 CST BufferChan send begin2014-05-09 10:41:27.5647026 +0800 CST BufferChan send end2014-05-09 10:41:37.5662746 +0800 CST BufferChan recv begin2014-05-09 10:41:37.5662746 +0800 CST BufferChan recv end

可以發現帶Buffer的chan收/發完成時間相差了10秒.