select default

R=r
OCL=18646
CL=18646

src/cmd/gc/subr.c

@@ -1445,6 +1445,9 @@ isselect(Node *n)
 	if(s == n->sym)
 		return 1;
 	s = pkglookup("selectrecv", "sys");
+	if(s == n->sym)
+		return 1;
+	s = pkglookup("selectdefault", "sys");
 	if(s == n->sym)
 		return 1;
 	return 0;

src/cmd/gc/sys.go

@@ -68,6 +68,7 @@ export func	chansend2(hchan *chan any, elem any) (pres bool);
 export func	newselect(size int) (sel *byte);
 export func	selectsend(sel *byte, hchan *chan any, elem any) (selected bool);
 export func	selectrecv(sel *byte, hchan *chan any, elem *any) (selected bool);
+export func	selectdefault(sel *byte) (selected bool);
 export func	selectgo(sel *byte);
 
 export func	newarray(nel int, cap int, width int) (ary *[]any);

src/cmd/gc/sysimport.c

@@ -53,6 +53,7 @@ char *sysimport =
 	"export func sys.newselect (size int) (sel *uint8)\n"
 	"export func sys.selectsend (sel *uint8, hchan *chan any, elem any) (selected bool)\n"
 	"export func sys.selectrecv (sel *uint8, hchan *chan any, elem *any) (selected bool)\n"
+	"export func sys.selectdefault (sel *uint8) (selected bool)\n"
 	"export func sys.selectgo (sel *uint8)\n"
 	"export func sys.newarray (nel int, cap int, width int) (ary *[]any)\n"
 	"export func sys.arraysliced (old *[]any, lb int, hb int, width int) (ary *[]any)\n"

src/cmd/gc/walk.c

@@ -1246,6 +1246,8 @@ selcase(Node *n, Node *var)
 	Node *a, *r, *on, *c;
 	Type *t;
 
+	if(n->left == N)
+		goto dflt;
 	c = n->left;
 	if(c->op == ORECV)
 		goto recv;
@@ -1329,6 +1331,14 @@ recv2:
 	r = list(a, r);
 	a = var;			// sel-var
 	r = list(a, r);
+	goto out;
+
+dflt:
+	// selectdefault(sel *byte);
+	on = syslook("selectdefault", 0);
+	a = var;
+	r = a;				// sel-var
+	goto out;
 
 out:
 	a = nod(OCALL, on, r);
@@ -1367,8 +1377,8 @@ walkselect(Node *sel)
 {
 	Iter iter;
 	Node *n, *oc, *on, *r;
-	Node *var, *bod, *res;
-	int count;
+	Node *var, *bod, *res, *def;
+	int count, op;
 	int32 lno;
 
 	lno = setlineno(sel);
@@ -1385,6 +1395,7 @@ walkselect(Node *sel)
 	res = N;	// entire select body
 	bod = N;	// body of each case
 	oc = N;		// last case
+	def = N;	// default case
 
 	for(count=0; n!=N; n=listnext(&iter)) {
 		setlineno(n);
@@ -1395,15 +1406,22 @@ walkselect(Node *sel)
 			break;
 
 		case OXCASE:
-			switch(n->left->op) {
+			if(n->left == N) {
+				op = ORECV;	// actual value not used
+				if(def != N)
+					yyerror("only one default select allowed");
+				def = n;
+			} else
+				op = n->left->op;
+			switch(op) {
 			default:
-				yyerror("select cases must be send or recv");
+				yyerror("select cases must be send, recv or default");
 				break;
 
 			case OAS:
 				// convert new syntax (a=recv(chan)) to (recv(a,chan))
 				if(n->left->right == N || n->left->right->op != ORECV) {
-					yyerror("select cases must be send or recv");
+					yyerror("select cases must be send, recv or default");
 					break;
 				}
 				n->left->right->right = n->left->right->left;
@@ -1419,6 +1437,8 @@ walkselect(Node *sel)
 				oc = selcase(n, var);
 				res = list(res, oc);
 				break;
+
+				
 			}
 			bod = N;
 			count++;

src/runtime/chan.c

@@ -497,14 +497,14 @@ sys·selectrecv(Select *sel, Hchan *c, ...)
 	}
 }
 
+
+// selectrecv(sel *byte) (selected bool);
 void
-sys·selectdefault(Select *sel)
+sys·selectdefault(Select *sel, ...)
 {
-	int32 i, eo;
+	int32 i;
 	Scase *cas;
-	Hchan *c;
 	
-	c = nil;
 	i = sel->ncase;
 	if(i >= sel->tcase)
 		throw("selectdefault: too many cases");
@@ -512,13 +512,11 @@ sys·selectdefault(Select *sel)
 	cas = &sel->scase[i];
 
 	cas->pc = sys·getcallerpc(&sel);
-	cas->chan = c;
+	cas->chan = nil;
 
-	eo = rnd(sizeof(sel), sizeof(c));
-	eo = rnd(eo+sizeof(c), sizeof(byte*));
-	cas->so = rnd(eo+sizeof(byte*), 1);
+	cas->so = rnd(sizeof(sel), 1);
 	cas->send = 2;
-	cas->u.elemp = *(byte**)((byte*)&sel + eo);
+	cas->u.elemp = nil;
 
 	if(debug) {
 		prints("newselect s=");

src/runtime/runtime.c

@@ -4,7 +4,8 @@
 
 #include "runtime.h"
 
-int32	panicking = 0;
+int32	panicking	= 0;
+int32	maxround	= 8;
 
 int32
 gotraceback(void)
@@ -91,6 +92,8 @@ rnd(uint32 n, uint32 m)
 {
 	uint32 r;
 
+	if(m > maxround)
+		m = maxround;
 	r = n % m;
 	if(r)
 		n += m-r;

src/runtime/runtime.h

@@ -190,6 +190,7 @@ G*	allg;
 int32	goidgen;
 extern	int32	gomaxprocs;
 extern	int32	panicking;
+extern	int32	maxround;
 
 /*
  * common functions and data