gc, runtime: make range on channel safe for multiple goroutines

Fixes #397.

R=ken2
CC=golang-dev
https://golang.org/cl/3994043

src/cmd/gc/builtin.c.boot

@@ -67,6 +67,7 @@ char *runtimeimport =
 	"func \"\".makechan (elem *uint8, hint int64) chan any\n"
 	"func \"\".chanrecv1 (hchan <-chan any) any\n"
 	"func \"\".chanrecv2 (hchan <-chan any) (elem any, pres bool)\n"
+	"func \"\".chanrecv3 (hchan <-chan any) (elem any, closed bool)\n"
 	"func \"\".chansend1 (hchan chan<- any, elem any)\n"
 	"func \"\".chansend2 (hchan chan<- any, elem any) bool\n"
 	"func \"\".closechan (hchan any)\n"

src/cmd/gc/go.h

@@ -356,7 +356,7 @@ enum
 	OARRAY,
 	OARRAYBYTESTR, OARRAYRUNESTR,
 	OSTRARRAYBYTE, OSTRARRAYRUNE,
-	OAS, OAS2, OAS2MAPW, OAS2FUNC, OAS2RECV, OAS2MAPR, OAS2DOTTYPE, OASOP,
+	OAS, OAS2, OAS2MAPW, OAS2FUNC, OAS2RECV, OAS2RECVCLOSED, OAS2MAPR, OAS2DOTTYPE, OASOP,
 	OBAD,
 	OCALL, OCALLFUNC, OCALLMETH, OCALLINTER,
 	OCAP,

src/cmd/gc/range.c

@@ -93,6 +93,7 @@ walkrange(Node *n)
 	Node *ohv1, *hv1, *hv2;	// hidden (old) val 1, 2
 	Node *ha, *hit;	// hidden aggregate, iterator
 	Node *hn, *hp;	// hidden len, pointer
+	Node *hb;  // hidden bool
 	Node *a, *v1, *v2;	// not hidden aggregate, val 1, 2
 	Node *fn, *tmp;
 	NodeList *body, *init;
@@ -199,9 +200,15 @@ walkrange(Node *n)
 	case TCHAN:
 		hv1 = nod(OXXX, N, n);
 		tempname(hv1, t->type);
+		hb = nod(OXXX, N, N);
+		tempname(hb, types[TBOOL]);
 
-		n->ntest = nod(ONOT, nod(OCLOSED, ha, N), N);
-		n->ntest->ninit = list1(nod(OAS, hv1, nod(ORECV, ha, N)));
+		n->ntest = nod(ONOT, hb, N);
+		a = nod(OAS2RECVCLOSED, N, N);
+		a->typecheck = 1;
+		a->list = list(list1(hv1), hb);
+		a->rlist = list1(nod(ORECV, ha, N));
+		n->ntest->ninit = list1(a);
 		body = list1(nod(OAS, v1, hv1));
 		break;
 

src/cmd/gc/runtime.go

@@ -93,6 +93,7 @@ func mapiter2(hiter *any) (key any, val any)
 func makechan(elem *byte, hint int64) (hchan chan any)
 func chanrecv1(hchan <-chan any) (elem any)
 func chanrecv2(hchan <-chan any) (elem any, pres bool)
+func chanrecv3(hchan <-chan any) (elem any, closed bool)
 func chansend1(hchan chan<- any, elem any)
 func chansend2(hchan chan<- any, elem any) (pres bool)
 func closechan(hchan any)

src/cmd/gc/walk.c

@@ -404,6 +404,7 @@ walkstmt(Node **np)
 	case OAS2:
 	case OAS2DOTTYPE:
 	case OAS2RECV:
+	case OAS2RECVCLOSED:
 	case OAS2FUNC:
 	case OAS2MAPW:
 	case OAS2MAPR:
@@ -835,6 +836,19 @@ walkexpr(Node **np, NodeList **init)
 		n->op = OAS2FUNC;
 		goto as2func;
 
+	case OAS2RECVCLOSED:
+		// a = <-c; b = closed(c) but atomic
+		*init = concat(*init, n->ninit);
+		n->ninit = nil;
+		r = n->rlist->n;
+		walkexprlistsafe(n->list, init);
+		walkexpr(&r->left, init);
+		fn = chanfn("chanrecv3", 2, r->left->type);
+		r = mkcall1(fn, getoutargx(fn->type), init, r->left);
+		n->rlist->n = r;
+		n->op = OAS2FUNC;
+		goto as2func;
+
 	case OAS2MAPR:
 		// a,b = m[i];
 		*init = concat(*init, n->ninit);

src/pkg/runtime/chan.c

@@ -284,7 +284,7 @@ closed:
 }
 
 void
-runtime·chanrecv(Hchan* c, byte *ep, bool* pres)
+runtime·chanrecv(Hchan* c, byte *ep, bool *pres, bool *closed)
 {
 	SudoG *sg;
 	G *gp;
@@ -299,6 +299,9 @@ runtime·chanrecv(Hchan* c, byte *ep, bool* pres)
 		runtime·printf("chanrecv: chan=%p\n", c);
 
 	runtime·lock(c);
+	if(closed != nil)
+		*closed = false;
+
 loop:
 	if(c->dataqsiz > 0)
 		goto asynch;
@@ -387,6 +390,8 @@ asynch:
 	return;
 
 closed:
+	if(closed != nil)
+		*closed = true;
 	c->elemalg->copy(c->elemsize, ep, nil);
 	c->closed |= Rclosed;
 	incerr(c);
@@ -441,7 +446,7 @@ runtime·chanrecv1(Hchan* c, ...)
 	o = runtime·rnd(sizeof(c), Structrnd);
 	ae = (byte*)&c + o;
 
-	runtime·chanrecv(c, ae, nil);
+	runtime·chanrecv(c, ae, nil, nil);
 }
 
 // chanrecv2(hchan *chan any) (elem any, pres bool);
@@ -457,7 +462,23 @@ runtime·chanrecv2(Hchan* c, ...)
 	o = runtime·rnd(o+c->elemsize, 1);
 	ap = (byte*)&c + o;
 
-	runtime·chanrecv(c, ae, ap);
+	runtime·chanrecv(c, ae, ap, nil);
+}
+
+// chanrecv3(hchan *chan any) (elem any, closed bool);
+#pragma textflag 7
+void
+runtime·chanrecv3(Hchan* c, ...)
+{
+	int32 o;
+	byte *ae, *ac;
+
+	o = runtime·rnd(sizeof(c), Structrnd);
+	ae = (byte*)&c + o;
+	o = runtime·rnd(o+c->elemsize, 1);
+	ac = (byte*)&c + o;
+
+	runtime·chanrecv(c, ae, nil, ac);
 }
 
 // newselect(size uint32) (sel *byte);

src/pkg/runtime/reflect.goc

@@ -75,7 +75,7 @@ func chansend(ch *byte, val *byte, pres *bool) {
 }
 
 func chanrecv(ch *byte, val *byte, pres *bool) {
-	runtime·chanrecv((Hchan*)ch, val, pres);
+	runtime·chanrecv((Hchan*)ch, val, pres, nil);
 }
 
 func chanclose(ch *byte) {

src/pkg/runtime/runtime.h

@@ -581,7 +581,7 @@ Hmap*	runtime·makemap_c(Type*, Type*, int64);
 
 Hchan*	runtime·makechan_c(Type*, int64);
 void	runtime·chansend(Hchan*, void*, bool*);
-void	runtime·chanrecv(Hchan*, void*, bool*);
+void	runtime·chanrecv(Hchan*, void*, bool*, bool*);
 void	runtime·chanclose(Hchan*);
 bool	runtime·chanclosed(Hchan*);
 int32	runtime·chanlen(Hchan*);