带buffer的chan能同步吗?

具体看下面2个例子:

无 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
}

第二个程序(有buffer的chan)无法保证收/发同步, 导致main退出时 println 还未执行.
说明带buffer的chan是不能保证收/发同步.

下面是一个构造的测试例子
http://play.golang.org/p/vQQCv9nG15

package main

import (
    "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 上的结果(play上的是假时间):

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

在本机运行的结果:

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

可以发现带Buffer的chan收/发完成时间相差了10秒.

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