os/exec: Wait waits for EOF on stdout pipe

[gopherbot]

by ikari.shinji.eva:

What steps will reproduce the problem?
run http://play.golang.org/p/VwzEpAHA7M (Cannot run in playground, please run it on a
mac/linux)

What is the expected output?
all 3 steps should be returned immediately

What do you see instead?
the 2nd step, when redirect Stdout to a bytes.buffer, spend 3 seconds, which means it
returned after  the background process ("sleep 3 &") return

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
Mac OS X 10.9.1 (13B42)

Which version are you using?  (run 'go version')
go version go1.2 darwin/amd64

Please provide any additional information below.
in exec.Cmd.Wait, it will wait all c.goroutine's errch chan, no matter if the process is
finished or running in background. It's where the call blocks.

[rsc]

Comment 1:

It's not clear that we can do much better. If we stop reading from the pipe before EOF,
there is a race and we might not have gotten all the results. I really think this is the
best we can do. It's fundamental to how Unix works. What if the sleep was going to print
some more output?

Status changed to WorkingAsIntended.