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io: Avoid race condition in pipe.

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One goroutine started up and was waiting in rw.  Then another
goroutine decided to close the pipe.  The closing goroutine
stalled calling p.io.Lock() in pipeHalf.close.  (This happened
in gccgo).  If the closing goroutine had been able to set the
ioclosed flag, it would have gone on to tell the runner that
the pipe was closed, which would then send an EINVAL to the
goroutine sleeping in rw.  Unlocking p.io before sleeping in
rw avoids the race.

R=rsc, rsc1
CC=golang-dev
https://golang.org/cl/1682048
This commit is contained in:
Ian Lance Taylor 2010-06-30 13:14:46 -07:00
parent d3c3c15b17
commit 7c1be45f58
1 changed files with 2 additions and 1 deletions
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3
src/pkg/io/pipe.go
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@ -144,10 +144,11 @@ func (p *pipeHalf) rw(data []byte) (n int, err os.Error) {
// Run i/o operation. // Run i/o operation.
// Check ioclosed flag under lock to make sure we're still allowed to do i/o. // Check ioclosed flag under lock to make sure we're still allowed to do i/o.
p.io.Lock() p.io.Lock()
defer p.io.Unlock()
if p.ioclosed { if p.ioclosed {
p.io.Unlock()
return 0, os.EINVAL return 0, os.EINVAL
} }
p.io.Unlock()
p.c1 <- data p.c1 <- data
res := <-p.c2 res := <-p.c2
return res.n, res.err return res.n, res.err