replace non-blocking send, receive syntax with select

R=golang-dev, nigeltao, niemeyer, r
CC=golang-dev
https://golang.org/cl/4079053

27 files changed, 402 insertions, 205 deletions

diff --git a/src/pkg/compress/flate/deflate_test.go b/src/pkg/compress/flate/deflate_test.go
index 3db955609d..68dcd7bcc5 100644
--- a/src/pkg/compress/flate/deflate_test.go
+++ b/src/pkg/compress/flate/deflate_test.go
@@ -116,9 +116,16 @@ func (b *syncBuffer) Read(p []byte) (n int, err os.Error) {
 	panic("unreachable")
 }
 
+func (b *syncBuffer) signal() {
+	select {
+	case b.ready <- true:
+	default:
+	}
+}
+
 func (b *syncBuffer) Write(p []byte) (n int, err os.Error) {
 	n, err = b.buf.Write(p)
-	_ = b.ready <- true
+	b.signal()
 	return
 }
 
@@ -128,12 +135,12 @@ func (b *syncBuffer) WriteMode() {
 
 func (b *syncBuffer) ReadMode() {
 	b.mu.Unlock()
-	_ = b.ready <- true
+	b.signal()
 }
 
 func (b *syncBuffer) Close() os.Error {
 	b.closed = true
-	_ = b.ready <- true
+	b.signal()
 	return nil
 }
 
diff --git a/src/pkg/exp/draw/x11/conn.go b/src/pkg/exp/draw/x11/conn.go
index da2181536f..e28fb21706 100644
--- a/src/pkg/exp/draw/x11/conn.go
+++ b/src/pkg/exp/draw/x11/conn.go
@@ -122,10 +122,13 @@ func (c *conn) writeSocket() {
 func (c *conn) Screen() draw.Image { return c.img }
 
 func (c *conn) FlushImage() {
-	// We do the send (the <- operator) in an expression context, rather than in
-	// a statement context, so that it does not block, and fails if the buffered
-	// channel is full (in which case there already is a flush request pending).
-	_ = c.flush <- false
+	select {
+	case c.flush <- false:
+		// Flush notification sent.
+	default:
+		// Could not send.
+		// Flush notification must be pending already.
+	}
 }
 
 func (c *conn) Close() os.Error {
diff --git a/src/pkg/fmt/print.go b/src/pkg/fmt/print.go
index 96029a8789..d6dc8eb3da 100644
--- a/src/pkg/fmt/print.go
+++ b/src/pkg/fmt/print.go
@@ -74,15 +74,42 @@ type pp struct {
 	fmt     fmt
 }
 
-// A leaky bucket of reusable pp structures.
-var ppFree = make(chan *pp, 100)
+// A cache holds a set of reusable objects.
+// The buffered channel holds the currently available objects.
+// If more are needed, the cache creates them by calling new.
+type cache struct {
+	saved chan interface{}
+	new   func() interface{}
+}
+
+func (c *cache) put(x interface{}) {
+	select {
+	case c.saved <- x:
+		// saved in cache
+	default:
+		// discard
+	}
+}
 
-// Allocate a new pp struct.  Probably can grab the previous one from ppFree.
-func newPrinter() *pp {
-	p, ok := <-ppFree
-	if !ok {
-		p = new(pp)
+func (c *cache) get() interface{} {
+	select {
+	case x := <-c.saved:
+		return x // reused from cache
+	default:
+		return c.new()
 	}
+	panic("not reached")
+}
+
+func newCache(f func() interface{}) *cache {
+	return &cache{make(chan interface{}, 100), f}
+}
+
+var ppFree = newCache(func() interface{} { return new(pp) })
+
+// Allocate a new pp struct or grab a cached one.
+func newPrinter() *pp {
+	p := ppFree.get().(*pp)
 	p.fmt.init(&p.buf)
 	return p
 }
@@ -94,7 +121,7 @@ func (p *pp) free() {
 		return
 	}
 	p.buf.Reset()
-	_ = ppFree <- p
+	ppFree.put(p)
 }
 
 func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }
diff --git a/src/pkg/fmt/scan.go b/src/pkg/fmt/scan.go
index ebbb17155e..a408c42aaf 100644
--- a/src/pkg/fmt/scan.go
+++ b/src/pkg/fmt/scan.go
@@ -303,15 +303,11 @@ func (r *readRune) ReadRune() (rune int, size int, err os.Error) {
 }
 
 
-// A leaky bucket of reusable ss structures.
-var ssFree = make(chan *ss, 100)
+var ssFree = newCache(func() interface{} { return new(ss) })
 
-// Allocate a new ss struct.  Probably can grab the previous one from ssFree.
+// Allocate a new ss struct or grab a cached one.
 func newScanState(r io.Reader, nlIsSpace bool) *ss {
-	s, ok := <-ssFree
-	if !ok {
-		s = new(ss)
-	}
+	s := ssFree.get().(*ss)
 	if rr, ok := r.(readRuner); ok {
 		s.rr = rr
 	} else {
@@ -333,7 +329,7 @@ func (s *ss) free() {
 	}
 	s.buf.Reset()
 	s.rr = nil
-	_ = ssFree <- s
+	ssFree.put(s)
 }
 
 // skipSpace skips spaces and maybe newlines.
diff --git a/src/pkg/net/fd.go b/src/pkg/net/fd.go
index 896178f18e..2ba9296f31 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -220,11 +220,16 @@ func (s *pollServer) Run() {
 				nn, _ = s.pr.Read(scratch[0:])
 			}
 			// Read from channels
-			for fd, ok := <-s.cr; ok; fd, ok = <-s.cr {
-				s.AddFD(fd, 'r')
-			}
-			for fd, ok := <-s.cw; ok; fd, ok = <-s.cw {
-				s.AddFD(fd, 'w')
+		Update:
+			for {
+				select {
+				case fd := <-s.cr:
+					s.AddFD(fd, 'r')
+				case fd := <-s.cw:
+					s.AddFD(fd, 'w')
+				default:
+					break Update
+				}
 			}
 		} else {
 			netfd := s.LookupFD(fd, mode)
diff --git a/src/pkg/net/server_test.go b/src/pkg/net/server_test.go
index 543227f7d1..3dda500e58 100644
--- a/src/pkg/net/server_test.go
+++ b/src/pkg/net/server_test.go
@@ -140,13 +140,16 @@ func runPacket(t *testing.T, network, addr string, listening chan<- string, done
 	listening <- c.LocalAddr().String()
 	c.SetReadTimeout(10e6) // 10ms
 	var buf [1000]byte
+Run:
 	for {
 		n, addr, err := c.ReadFrom(buf[0:])
 		if e, ok := err.(Error); ok && e.Timeout() {
-			if done <- 1 {
-				break
+			select {
+			case done <- 1:
+				break Run
+			default:
+				continue Run
 			}
-			continue
 		}
 		if err != nil {
 			break
diff --git a/src/pkg/netchan/common.go b/src/pkg/netchan/common.go
index 56c0b25199..6c085484e5 100644
--- a/src/pkg/netchan/common.go
+++ b/src/pkg/netchan/common.go
@@ -256,7 +256,10 @@ func (nch *netChan) send(val reflect.Value) {
 		nch.sendCh = make(chan reflect.Value, nch.size)
 		go nch.sender()
 	}
-	if ok := nch.sendCh <- val; !ok {
+	select {
+	case nch.sendCh <- val:
+		// ok
+	default:
 		// TODO: should this be more resilient?
 		panic("netchan: remote sender sent more values than allowed")
 	}
@@ -318,8 +321,11 @@ func (nch *netChan) acked() {
 	if nch.dir != Send {
 		panic("recv on wrong direction of channel")
 	}
-	if ok := nch.ackCh <- true; !ok {
-		panic("netchan: remote receiver sent too many acks")
+	select {
+	case nch.ackCh <- true:
+		// ok
+	default:
 		// TODO: should this be more resilient?
+		panic("netchan: remote receiver sent too many acks")
 	}
 }
diff --git a/src/pkg/netchan/import.go b/src/pkg/netchan/import.go
index a694fb41f6..d1e9bbd406 100644
--- a/src/pkg/netchan/import.go
+++ b/src/pkg/netchan/import.go
@@ -91,11 +91,13 @@ func (imp *Importer) run() {
 			}
 			if err.Error != "" {
 				impLog("response error:", err.Error)
-				if sent := imp.errors <- os.ErrorString(err.Error); !sent {
+				select {
+				case imp.errors <- os.ErrorString(err.Error):
+					continue // errors are not acknowledged
+				default:
 					imp.shutdown()
 					return
 				}
-				continue // errors are not acknowledged.
 			}
 		case payClosed:
 			nch := imp.getChan(hdr.Id, false)
diff --git a/src/pkg/os/inotify/inotify_linux.go b/src/pkg/os/inotify/inotify_linux.go
index 1e74c7fbc5..9d7a074424 100644
--- a/src/pkg/os/inotify/inotify_linux.go
+++ b/src/pkg/os/inotify/inotify_linux.go
@@ -153,7 +153,11 @@ func (w *Watcher) readEvents() {
 	for {
 		n, errno = syscall.Read(w.fd, buf[0:])
 		// See if there is a message on the "done" channel
-		_, done := <-w.done
+		var done bool
+		select {
+		case done = <-w.done:
+		default:
+		}
 
 		// If EOF or a "done" message is received
 		if n == 0 || done {
diff --git a/src/pkg/path/path_test.go b/src/pkg/path/path_test.go
index 6b4be07a95..ab0b48ad6a 100644
--- a/src/pkg/path/path_test.go
+++ b/src/pkg/path/path_test.go
@@ -256,8 +256,11 @@ func TestWalk(t *testing.T) {
 	// 2) handle errors, expect none
 	errors := make(chan os.Error, 64)
 	Walk(tree.name, v, errors)
-	if err, ok := <-errors; ok {
+	select {
+	case err := <-errors:
 		t.Errorf("no error expected, found: %s", err)
+	default:
+		// ok
 	}
 	checkMarks(t)
 
@@ -276,14 +279,21 @@ func TestWalk(t *testing.T) {
 		errors = make(chan os.Error, 64)
 		os.Chmod(Join(tree.name, tree.entries[1].name), 0)
 		Walk(tree.name, v, errors)
+	Loop:
 		for i := 1; i <= 2; i++ {
-			if _, ok := <-errors; !ok {
+			select {
+			case <-errors:
+				// ok
+			default:
 				t.Errorf("%d. error expected, none found", i)
-				break
+				break Loop
 			}
 		}
-		if err, ok := <-errors; ok {
+		select {
+		case err := <-errors:
 			t.Errorf("only two errors expected, found 3rd: %v", err)
+		default:
+			// ok
 		}
 		// the inaccessible subtrees were marked manually
 		checkMarks(t)
diff --git a/src/pkg/rpc/client.go b/src/pkg/rpc/client.go
index 601c49715b..6f028c10d9 100644
--- a/src/pkg/rpc/client.go
+++ b/src/pkg/rpc/client.go
@@ -58,7 +58,7 @@ func (client *Client) send(c *Call) {
 	if client.shutdown != nil {
 		c.Error = client.shutdown
 		client.mutex.Unlock()
-		_ = c.Done <- c // do not block
+		c.done()
 		return
 	}
 	c.seq = client.seq
@@ -102,16 +102,14 @@ func (client *Client) input() {
 			// Empty strings should turn into nil os.Errors
 			c.Error = nil
 		}
-		// We don't want to block here.  It is the caller's responsibility to make
-		// sure the channel has enough buffer space. See comment in Go().
-		_ = c.Done <- c // do not block
+		c.done()
 	}
 	// Terminate pending calls.
 	client.mutex.Lock()
 	client.shutdown = err
 	for _, call := range client.pending {
 		call.Error = err
-		_ = call.Done <- call // do not block
+		call.done()
 	}
 	client.mutex.Unlock()
 	if err != os.EOF || !client.closing {
@@ -119,6 +117,16 @@ func (client *Client) input() {
 	}
 }
 
+func (call *Call) done() {
+	select {
+	case call.Done <- call:
+		// ok
+	default:
+		// We don't want to block here.  It is the caller's responsibility to make
+		// sure the channel has enough buffer space. See comment in Go().
+	}
+}
+
 // NewClient returns a new Client to handle requests to the
 // set of services at the other end of the connection.
 func NewClient(conn io.ReadWriteCloser) *Client {
@@ -233,7 +241,7 @@ func (client *Client) Go(serviceMethod string, args interface{}, reply interface
 	c.Done = done
 	if client.shutdown != nil {
 		c.Error = client.shutdown
-		_ = c.Done <- c // do not block
+		c.done()
 		return c
 	}
 	client.send(c)
diff --git a/src/pkg/rpc/server_test.go b/src/pkg/rpc/server_test.go
index 355d51ce46..67b8762fa5 100644
--- a/src/pkg/rpc/server_test.go
+++ b/src/pkg/rpc/server_test.go
@@ -364,14 +364,12 @@ func TestSendDeadlock(t *testing.T) {
 		testSendDeadlock(client)
 		done <- true
 	}()
-	for i := 0; i < 50; i++ {
-		time.Sleep(100 * 1e6)
-		_, ok := <-done
-		if ok {
-			return
-		}
+	select {
+	case <-done:
+		return
+	case <-time.After(5e9):
+		t.Fatal("deadlock")
 	}
-	t.Fatal("deadlock")
 }
 
 func testSendDeadlock(client *Client) {
diff --git a/src/pkg/time/sleep_test.go b/src/pkg/time/sleep_test.go
index 4007db561a..8bf599c3e1 100644
--- a/src/pkg/time/sleep_test.go
+++ b/src/pkg/time/sleep_test.go
@@ -120,10 +120,12 @@ func TestAfterStop(t *testing.T) {
 		t.Fatalf("failed to stop event 1")
 	}
 	<-c2
-	_, ok0 := <-t0.C
-	_, ok1 := <-c1
-	if ok0 || ok1 {
-		t.Fatalf("events were not stopped")
+	select {
+	case <-t0.C:
+		t.Fatalf("event 0 was not stopped")
+	case <-c1:
+		t.Fatalf("event 1 was not stopped")
+	default:
 	}
 	if t1.Stop() {
 		t.Fatalf("Stop returned true twice")
diff --git a/src/pkg/time/tick.go b/src/pkg/time/tick.go
index ddd7272702..6c21bf19b9 100644
--- a/src/pkg/time/tick.go
+++ b/src/pkg/time/tick.go
@@ -22,8 +22,12 @@ type Ticker struct {
 
 // Stop turns off a ticker.  After Stop, no more ticks will be sent.
 func (t *Ticker) Stop() {
-	// Make it non-blocking so multiple Stops don't block.
-	_ = t.shutdown <- true
+	select {
+	case t.shutdown <- true:
+		// ok
+	default:
+		// Stop in progress already
+	}
 }
 
 // Tick is a convenience wrapper for NewTicker providing access to the ticking
@@ -106,7 +110,8 @@ func tickerLoop() {
 			// that need it and determining the next wake time.
 			// TODO(r): list should be sorted in time order.
 			for t := tickers; t != nil; t = t.next {
-				if _, ok := <-t.shutdown; ok {
+				select {
+				case <-t.shutdown:
 					// Ticker is done; remove it from list.
 					if prev == nil {
 						tickers = t.next
@@ -114,6 +119,7 @@ func tickerLoop() {
 						prev.next = t.next
 					}
 					continue
+				default:
 				}
 				if t.nextTick <= now {
 					if len(t.c) == 0 {
diff --git a/src/pkg/time/tick_test.go b/src/pkg/time/tick_test.go
index f2304a14e3..4dcb63956b 100644
--- a/src/pkg/time/tick_test.go
+++ b/src/pkg/time/tick_test.go
@@ -29,9 +29,11 @@ func TestTicker(t *testing.T) {
 	}
 	// Now test that the ticker stopped
 	Sleep(2 * Delta)
-	_, received := <-ticker.C
-	if received {
+	select {
+	case <-ticker.C:
 		t.Fatal("Ticker did not shut down")
+	default:
+		// ok
 	}
 }
 
diff --git a/test/chan/nonblock.go b/test/chan/nonblock.go
index 52f04bfb12..33afb32916 100644
--- a/test/chan/nonblock.go
+++ b/test/chan/nonblock.go
@@ -76,7 +76,6 @@ func main() {
 	var i64 int64
 	var b bool
 	var s string
-	var ok bool
 
 	var sync = make(chan bool)
 
@@ -86,35 +85,45 @@ func main() {
 		cb := make(chan bool, buffer)
 		cs := make(chan string, buffer)
 
-		i32, ok = <-c32
-		if ok {
+		select {
+		case i32 = <-c32:
 			panic("blocked i32sender")
+		default:
 		}
 
-		i64, ok = <-c64
-		if ok {
+		select {
+		case i64 = <-c64:
 			panic("blocked i64sender")
+		default:
 		}
 
-		b, ok = <-cb
-		if ok {
+		select {
+		case b = <-cb:
 			panic("blocked bsender")
+		default:
 		}
 
-		s, ok = <-cs
-		if ok {
+		select {
+		case s = <-cs:
 			panic("blocked ssender")
+		default:
 		}
 
 		go i32receiver(c32, sync)
 		try := 0
-		for !(c32 <- 123) {
-			try++
-			if try > maxTries {
-				println("i32receiver buffer=", buffer)
-				panic("fail")
+	Send32:
+		for {
+			select {
+			case c32 <- 123:
+				break Send32
+			default:
+				try++
+				if try > maxTries {
+					println("i32receiver buffer=", buffer)
+					panic("fail")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		<-sync
 
@@ -123,13 +132,19 @@ func main() {
 			<-sync
 		}
 		try = 0
-		for i32, ok = <-c32; !ok; i32, ok = <-c32 {
-			try++
-			if try > maxTries {
-				println("i32sender buffer=", buffer)
-				panic("fail")
+	Recv32:
+		for {
+			select {
+			case i32 = <-c32:
+				break Recv32
+			default:
+				try++
+				if try > maxTries {
+					println("i32sender buffer=", buffer)
+					panic("fail")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		if i32 != 234 {
 			panic("i32sender value")
@@ -140,12 +155,18 @@ func main() {
 
 		go i64receiver(c64, sync)
 		try = 0
-		for !(c64 <- 123456) {
-			try++
-			if try > maxTries {
-				panic("i64receiver")
+	Send64:
+		for {
+			select {
+			case c64 <- 123456:
+				break Send64
+			default:
+				try++
+				if try > maxTries {
+					panic("i64receiver")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		<-sync
 
@@ -154,12 +175,18 @@ func main() {
 			<-sync
 		}
 		try = 0
-		for i64, ok = <-c64; !ok; i64, ok = <-c64 {
-			try++
-			if try > maxTries {
-				panic("i64sender")
+	Recv64:
+		for {
+			select {
+			case i64 = <-c64:
+				break Recv64
+			default:
+				try++
+				if try > maxTries {
+					panic("i64sender")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		if i64 != 234567 {
 			panic("i64sender value")
@@ -170,12 +197,18 @@ func main() {
 
 		go breceiver(cb, sync)
 		try = 0
-		for !(cb <- true) {
-			try++
-			if try > maxTries {
-				panic("breceiver")
+	SendBool:
+		for {
+			select {
+			case cb <- true:
+				break SendBool
+			default:
+				try++
+				if try > maxTries {
+					panic("breceiver")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		<-sync
 
@@ -184,12 +217,18 @@ func main() {
 			<-sync
 		}
 		try = 0
-		for b, ok = <-cb; !ok; b, ok = <-cb {
-			try++
-			if try > maxTries {
-				panic("bsender")
+	RecvBool:
+		for {
+			select {
+			case b = <-cb:
+				break RecvBool
+			default:
+				try++
+				if try > maxTries {
+					panic("bsender")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		if !b {
 			panic("bsender value")
@@ -200,12 +239,18 @@ func main() {
 
 		go sreceiver(cs, sync)
 		try = 0
-		for !(cs <- "hello") {
-			try++
-			if try > maxTries {
-				panic("sreceiver")
+	SendString:
+		for {
+			select {
+			case cs <- "hello":
+				break SendString
+			default:
+				try++
+				if try > maxTries {
+					panic("sreceiver")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		<-sync
 
@@ -214,12 +259,18 @@ func main() {
 			<-sync
 		}
 		try = 0
-		for s, ok = <-cs; !ok; s, ok = <-cs {
-			try++
-			if try > maxTries {
-				panic("ssender")
+	RecvString:
+		for {
+			select {
+			case s = <-cs:
+				break RecvString
+			default:
+				try++
+				if try > maxTries {
+					panic("ssender")
+				}
+				sleep()
 			}
-			sleep()
 		}
 		if s != "hello again" {
 			panic("ssender value")
diff --git a/test/chan/perm.go b/test/chan/perm.go
index d08c035193..c725829d13 100644
--- a/test/chan/perm.go
+++ b/test/chan/perm.go
@@ -9,49 +9,46 @@ package main
 var (
 	cr <-chan int
 	cs chan<- int
-	c chan int
+	c  chan int
 )
 
 func main() {
-	cr = c		// ok
-	cs = c		// ok
-	c = cr		// ERROR "illegal types|incompatible|cannot"
-	c = cs		// ERROR "illegal types|incompatible|cannot"
-	cr = cs	// ERROR "illegal types|incompatible|cannot"
-	cs = cr	// ERROR "illegal types|incompatible|cannot"
-
-	c <- 0		// ok
-	ok := c <- 0	// ok
-	_ = ok
-	<-c		// ok
-	x, ok := <-c	// ok
-	_, _ = x, ok
-
-	cr <- 0	// ERROR "send"
-	ok = cr <- 0	// ERROR "send"
-	_ = ok
-	<-cr		// ok
-	x, ok = <-cr	// ok
-	_, _ = x, ok
-
-	cs <- 0	// ok
-	ok = cs <- 0	// ok
-	_ = ok
-	<-cs		// ERROR "receive"
-	x, ok = <-cs	// ERROR "receive"
-	_, _ = x, ok
+	cr = c  // ok
+	cs = c  // ok
+	c = cr  // ERROR "illegal types|incompatible|cannot"
+	c = cs  // ERROR "illegal types|incompatible|cannot"
+	cr = cs // ERROR "illegal types|incompatible|cannot"
+	cs = cr // ERROR "illegal types|incompatible|cannot"
+
+	c <- 0 // ok
+	<-c    // ok
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	//	x, ok := <-c	// ok
+	//	_, _ = x, ok
+
+	cr <- 0 // ERROR "send"
+	<-cr    // ok
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	//	x, ok = <-cr	// ok
+	//	_, _ = x, ok
+
+	cs <- 0 // ok
+	<-cs    // ERROR "receive"
+	////TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	////	x, ok = <-cs	// ERROR "receive"
+	////	_, _ = x, ok
 
 	select {
-	case c <- 0:	// ok
-	case x := <-c:	// ok
+	case c <- 0: // ok
+	case x := <-c: // ok
 		_ = x
 
-	case cr <- 0:	// ERROR "send"
-	case x := <-cr:	// ok
+	case cr <- 0: // ERROR "send"
+	case x := <-cr: // ok
 		_ = x
 
-	case cs <- 0:	// ok
-	case x := <-cs:	// ERROR "receive"
+	case cs <- 0: // ok
+	case x := <-cs: // ERROR "receive"
 		_ = x
 	}
 }
diff --git a/test/closedchan.go b/test/closedchan.go
index 8126d5a4e4..46d9d0f5d2 100644
--- a/test/closedchan.go
+++ b/test/closedchan.go
@@ -21,14 +21,21 @@ type Chan interface {
 	Impl() string
 }
 
-// direct channel operations
+// direct channel operations when possible
 type XChan chan int
+
 func (c XChan) Send(x int) {
 	c <- x
 }
 
 func (c XChan) Nbsend(x int) bool {
-	return c <- x
+	select {
+	case c <- x:
+		return true
+	default:
+		return false
+	}
+	panic("nbsend")
 }
 
 func (c XChan) Recv() int {
@@ -36,8 +43,13 @@ func (c XChan) Recv() int {
 }
 
 func (c XChan) Nbrecv() (int, bool) {
-	x, ok := <-c
-	return x, ok
+	select {
+	case x := <-c:
+		return x, true
+	default:
+		return 0, false
+	}
+	panic("nbrecv")
 }
 
 func (c XChan) Close() {
@@ -54,6 +66,7 @@ func (c XChan) Impl() string {
 
 // indirect operations via select
 type SChan chan int
+
 func (c SChan) Send(x int) {
 	select {
 	case c <- x:
@@ -62,10 +75,10 @@ func (c SChan) Send(x int) {
 
 func (c SChan) Nbsend(x int) bool {
 	select {
-	case c <- x:
-		return true
 	default:
 		return false
+	case c <- x:
+		return true
 	}
 	panic("nbsend")
 }
@@ -80,10 +93,10 @@ func (c SChan) Recv() int {
 
 func (c SChan) Nbrecv() (int, bool) {
 	select {
-	case x := <-c:
-		return x, true
 	default:
 		return 0, false
+	case x := <-c:
+		return x, true
 	}
 	panic("nbrecv")
 }
@@ -100,6 +113,62 @@ func (c SChan) Impl() string {
 	return "(select)"
 }
 
+// indirect operations via larger selects
+var dummy = make(chan bool)
+
+type SSChan chan int
+
+func (c SSChan) Send(x int) {
+	select {
+	case c <- x:
+	case <-dummy:
+	}
+}
+
+func (c SSChan) Nbsend(x int) bool {
+	select {
+	default:
+		return false
+	case <-dummy:
+	case c <- x:
+		return true
+	}
+	panic("nbsend")
+}
+
+func (c SSChan) Recv() int {
+	select {
+	case <-dummy:
+	case x := <-c:
+		return x
+	}
+	panic("recv")
+}
+
+func (c SSChan) Nbrecv() (int, bool) {
+	select {
+	case <-dummy:
+	default:
+		return 0, false
+	case x := <-c:
+		return x, true
+	}
+	panic("nbrecv")
+}
+
+func (c SSChan) Close() {
+	close(c)
+}
+
+func (c SSChan) Closed() bool {
+	return closed(c)
+}
+
+func (c SSChan) Impl() string {
+	return "(select)"
+}
+
+
 func shouldPanic(f func()) {
 	defer func() {
 		if recover() == nil {
@@ -137,7 +206,7 @@ func test1(c Chan) {
 	}
 
 	// send should work with ,ok too: sent a value without blocking, so ok == true.
-	shouldPanic(func(){c.Nbsend(1)})
+	shouldPanic(func() { c.Nbsend(1) })
 
 	// the value should have been discarded.
 	if x := c.Recv(); x != 0 {
@@ -145,7 +214,7 @@ func test1(c Chan) {
 	}
 
 	// similarly Send.
-	shouldPanic(func(){c.Send(2)})
+	shouldPanic(func() { c.Send(2) })
 	if x := c.Recv(); x != 0 {
 		println("test1: recv on closed got non-zero after send on closed:", x, c.Impl())
 	}
@@ -195,9 +264,12 @@ func closedasync() chan int {
 func main() {
 	test1(XChan(closedsync()))
 	test1(SChan(closedsync()))
+	test1(SSChan(closedsync()))
 
 	testasync1(XChan(closedasync()))
 	testasync1(SChan(closedasync()))
+	testasync1(SSChan(closedasync()))
 	testasync2(XChan(closedasync()))
 	testasync2(SChan(closedasync()))
+	testasync2(SSChan(closedasync()))
 }
diff --git a/test/errchk b/test/errchk
index b0edd7a6b0..fbb021ce41 100755
--- a/test/errchk
+++ b/test/errchk
@@ -73,6 +73,7 @@ sub chk {
 	my @match;
 	foreach my $src (@{$src{$file}}) {
 		$line++;
+		next if $src =~ m|////|;  # double comment disables ERROR
 		next unless $src =~ m|// (GC_)?ERROR (.*)|;
 		$regexp = $2;
 		if($regexp !~ /^"([^"]*)"/) {
diff --git a/test/fixedbugs/bug016.go b/test/fixedbugs/bug016.go
index 461bcf82ac..1cdd8df084 100644
--- a/test/fixedbugs/bug016.go
+++ b/test/fixedbugs/bug016.go
@@ -1,4 +1,4 @@
-// ! $G $D/$F.go
+// errchk $G -e $D/$F.go
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,8 +7,8 @@
 package main
 
 func main() {
-	var i int = 100;
-	i = i << -3;  // BUG: should not compile (negative shift)
+	var i int = 100
+	i = i << -3 // ERROR "overflows"
 }
 
 /*
diff --git a/test/fixedbugs/bug069.go b/test/fixedbugs/bug069.go
index d6796cd72b..bf73163134 100644
--- a/test/fixedbugs/bug069.go
+++ b/test/fixedbugs/bug069.go
@@ -6,15 +6,16 @@
 
 package main
 
-func main(){
-	c := make(chan int);
-	ok := false;
-	var i int;
-
-	i, ok = <-c;  // works
-	_, _ = i, ok;
-
-	ca := new([2]chan int);
-	i, ok = <-(ca[0]);  // fails: c.go:11: bad shape across assignment - cr=1 cl=2
-	_, _ = i, ok;
+func main() {
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	//	c := make(chan int);
+	//	ok := false;
+	//	var i int;
+	//
+	//	i, ok = <-c;  // works
+	//	_, _ = i, ok;
+	//
+	//	ca := new([2]chan int);
+	//	i, ok = <-(ca[0]);  // fails: c.go:11: bad shape across assignment - cr=1 cl=2
+	//	_, _ = i, ok;
 }
diff --git a/test/fixedbugs/bug081.go b/test/fixedbugs/bug081.go
index ccb3699534..8d3d538c8f 100644
--- a/test/fixedbugs/bug081.go
+++ b/test/fixedbugs/bug081.go
@@ -1,12 +1,12 @@
-// ! $G $D/$F.go
+// errchk $G $D/$F.go
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main	
- 	
-const x x = 2;
+package main
+
+const x x = 2 // ERROR "loop"
 
 /*
 bug081.go:3: first constant must evaluate an expression
diff --git a/test/fixedbugs/bug196.go b/test/fixedbugs/bug196.go
index ea8ab0dc19..8cb9c9990d 100644
--- a/test/fixedbugs/bug196.go
+++ b/test/fixedbugs/bug196.go
@@ -13,11 +13,12 @@ var i int
 func multi() (int, int) { return 1, 2 }
 
 func xxx() {
-	var c chan int
-	x, ok := <-c
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	//	var c chan int
+	//	x, ok := <-c
 
 	var m map[int]int
-	x, ok = m[1]
+	x, ok := m[1]
 
 	var i interface{}
 	var xx int
diff --git a/test/fixedbugs/bug234.go b/test/fixedbugs/bug234.go
index b806ca64e9..9affad0430 100644
--- a/test/fixedbugs/bug234.go
+++ b/test/fixedbugs/bug234.go
@@ -7,16 +7,17 @@
 package main
 
 func main() {
-	c := make(chan int, 1)
-	c <- 100
-	x, ok := <-c
-	if x != 100 || !ok {
-		println("x=", x, " ok=", ok, " want 100, true")
-		panic("fail")
-	}
-	x, ok = <-c
-	if x != 0 || ok {
-		println("x=", x, " ok=", ok, " want 0, false")
-		panic("fail")
-	}
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	//	c := make(chan int, 1)
+	//	c <- 100
+	//	x, ok := <-c
+	//	if x != 100 || !ok {
+	//		println("x=", x, " ok=", ok, " want 100, true")
+	//		panic("fail")
+	//	}
+	//	x, ok = <-c
+	//	if x != 0 || ok {
+	//		println("x=", x, " ok=", ok, " want 0, false")
+	//		panic("fail")
+	//	}
 }
diff --git a/test/fixedbugs/bug242.go b/test/fixedbugs/bug242.go
index 5c21eaaf00..ad1cef8df4 100644
--- a/test/fixedbugs/bug242.go
+++ b/test/fixedbugs/bug242.go
@@ -101,10 +101,13 @@ func main() {
 
 	c := make(chan byte, 1)
 	c <- 'C'
+	//TODO(rsc): uncomment when this syntax is valid for receive+check closed
 	// 15          16
-	*f(), p1 = <-e1(c, 16)
+	//	*f(), p1 = <-e1(c, 16)
+	*f(), p1 = <-e1(c, 16), true // delete uncommenting above
 	// 17          18
-	*f(), p2 = <-e1(c, 18)
+	//	*f(), p2 = <-e1(c, 18)
+	*f(), p2, _ = 0, false, e1(c, 18) // delete when uncommenting above
 	a[17] += '0'
 	if !p1 || p2 {
 		println("bad chan check", i, p1, p2)
diff --git a/test/golden.out b/test/golden.out
index 83e8327a51..425771b4af 100644
--- a/test/golden.out
+++ b/test/golden.out
@@ -123,9 +123,6 @@ panic: interface conversion: *main.S is not main.I2: missing method Name
 
 == fixedbugs/
 
-=========== fixedbugs/bug016.go
-fixedbugs/bug016.go:11: constant -3 overflows uint
-
 =========== fixedbugs/bug027.go
 hi
 0 44444
@@ -148,9 +145,6 @@ inner loop top i 0
 do break
 broke
 
-=========== fixedbugs/bug081.go
-fixedbugs/bug081.go:9: typechecking loop
-
 =========== fixedbugs/bug093.go
 M
 
diff --git a/test/named1.go b/test/named1.go
index 600e502f9e..1776313f05 100644
--- a/test/named1.go
+++ b/test/named1.go
@@ -43,12 +43,9 @@ func main() {
 	_, b = m[2] // ERROR "cannot .* bool.*type Bool"
 	m[2] = 1, b // ERROR "cannot use.*type Bool.*as type bool"
 
-	b = c <- 1 // ERROR "cannot use.*type bool.*type Bool"
-	_ = b
-	asBool(c <- 1) // ERROR "cannot use.*type bool.*as type Bool"
-
-	_, b = <-c // ERROR "cannot .* bool.*type Bool"
-	_ = b
+	////TODO(rsc): uncomment when this syntax is valid for receive+check closed
+	////	_, b = <-c // ERROR "cannot .* bool.*type Bool"
+	////	_ = b
 
 	var inter interface{}
 	_, b = inter.(Map) // ERROR "cannot .* bool.*type Bool"