runtime support for default in select.

assumes cas->send == 2 for default case.

R=ken
OCL=18628
CL=18628

diff --git a/src/runtime/chan.c b/src/runtime/chan.c
index e9e3b3374fad47c606fb97ba73f6e127a47b58ce..6cabe634d46f49ae1ac04d72ab129a5578960063 100644 (file)
--- a/src/runtime/chan.c
+++ b/src/runtime/chan.c
@@ -52,7 +52,7 @@ struct        Scase
 {
        Hchan*  chan;                   // chan
        byte*   pc;                     // return pc
-       uint16  send;                   // 0-recv 1-send
+       uint16  send;                   // 0-recv 1-send 2-default
        uint16  so;                     // vararg of selected bool
        union {
                byte    elem[8];        // element (send)
@@ -504,7 +504,7 @@ void
 sys·selectgo(Select *sel)
 {
        uint32 p, o, i;
-       Scase *cas;
+       Scase *cas, *dfl;
        Hchan *c;
        SudoG *sg;
        G *gp;
@@ -542,8 +542,13 @@ sys·selectgo(Select *sel)
        lock(&chanlock);
 
        // pass 1 - look for something already waiting
+       dfl = nil;
        for(i=0; i<sel->ncase; i++) {
                cas = &sel->scase[o];
+               if(cas->send == 2) {    // default
+                       dfl = cas;
+                       continue;
+               }
                c = cas->chan;
                if(c->dataqsiz > 0) {
                        if(cas->send) {
@@ -569,6 +574,12 @@ sys·selectgo(Select *sel)
                if(o >= sel->ncase)
                        o -= sel->ncase;
        }
+       
+       if(dfl != nil) {
+               cas = dfl;
+               goto retc;
+       }
+               
 
        // pass 2 - enqueue on all chans
        for(i=0; i<sel->ncase; i++) {