spec, runtime, tests: send on closed channel panics

Close of closed channel panics.
Receive from closed channel never panics,
even if done repeatedly.

Fixes #1349.
Fixes #1419.

R=gri, iant, ken2, r, gri1, r2, iant2, rog, albert.strasheim, niemeyer, ejsherry
CC=golang-dev
https://golang.org/cl/3989042

1 files changed, 5 insertions, 9 deletions

diff --git a/test/chan/select3.go b/test/chan/select3.go
index a1a2ef50b5..9877b12a98 100644
--- a/test/chan/select3.go
+++ b/test/chan/select3.go
@@ -97,13 +97,9 @@ func main() {
 		}
 	})
 
-	// sending (a small number of times) to a closed channel is not specified
-	// but the current implementation doesn't block: test that different
-	// implementations behave the same
-	testBlock(never, func() {
-		for i := 0; i < 10; i++ {
-			closedch <- 7
-		}
+	// sending to a closed channel panics.
+	testPanic(always, func() {
+		closedch <- 7
 	})
 
 	// receiving from a non-ready channel always blocks
@@ -189,13 +185,13 @@ func main() {
 		}
 	})
 
-	// selects with closed channels don't block
+	// selects with closed channels behave like ordinary operations
 	testBlock(never, func() {
 		select {
 		case <-closedch:
 		}
 	})
-	testBlock(never, func() {
+	testPanic(always, func() {
 		select {
 		case closedch <- 7:
 		}