io: Pipes and ReadAt are safe to use concurrently.
Updates #1599.
R=golang-dev, bradfitz, rsc, r
CC=golang-dev
https://golang.org/cl/5708056
diff --git a/src/pkg/io/pipe.go b/src/pkg/io/pipe.go
index cf05e0c..69f9051 100644
--- a/src/pkg/io/pipe.go
+++ b/src/pkg/io/pipe.go
@@ -175,6 +175,10 @@
// with code expecting an io.Writer.
// Reads on one end are matched with writes on the other,
// copying data directly between the two; there is no internal buffering.
+// It is safe to call Read and Write in parallel with each other or with
+// Close. Close will complete once pending I/O is done. Parallel calls to
+// Read, and parallel calls to Write, are also safe:
+// the invidual calls will be gated sequentially.
func Pipe() (*PipeReader, *PipeWriter) {
p := new(pipe)
p.rwait.L = &p.l
