safe_write.go

package main

import (
        "bytes"
        "log"
        "os"
        "sync"

        "github.com/docker/docker/pkg/stdcopy"
)

type concurrentSafeBuffer struct {
        *bytes.Buffer
        m *sync.Mutex
}

func (c *concurrentSafeBuffer) Write(p []byte) (n int, err error) {
        c.m.Lock()
        n, err = c.Buffer.Write(p)
        c.m.Unlock()
        return
}

func (c *concurrentSafeBuffer) Read(p []byte) (n int, err error) {
        c.m.Lock()
        n, err = c.Buffer.Read(p)
        c.m.Unlock()
        return
}

func main() {
        stdcopystream := &concurrentSafeBuffer{
                Buffer: new(bytes.Buffer),
                m:      new(sync.Mutex),
        }

        go func() {
                _, err := stdcopy.StdCopy(os.Stdout, os.Stderr, stdcopystream)
                log.Fatal(err)
        }()

        outStream := stdcopy.NewStdWriter(stdcopystream, stdcopy.Stdout)
        errStream := stdcopy.NewStdWriter(stdcopystream, stdcopy.Stderr)

        go func() {
                for {
                        outStream.Write([]byte("out\n"))
                }
        }()

        for {
                errStream.Write([]byte("err\n"))
        }
}