runtime: add test for multiple concurrent channel consumers

There was a time (in the past) when this wasn't robust.

R=rsc, dvyukov
CC=golang-dev
https://golang.org/cl/4965058

diff --git a/src/pkg/runtime/chan_test.go b/src/pkg/runtime/chan_test.go
index 46ddfd7e88f52e9b206e63f0f4a291dedc72a99b..7cea906ceae6971b9b93d2fbc03a99e7d16eecfa 100644 (file)
--- a/src/pkg/runtime/chan_test.go
+++ b/src/pkg/runtime/chan_test.go
@@ -59,6 +59,57 @@ func TestPseudoRandomSend(t *testing.T) {
        t.Errorf("Want pseudo random, got %d zeros and %d ones", n0, n1)
 }
 
+func TestMultiConsumer(t *testing.T) {
+       const nwork = 23
+       const niter = 271828
+
+       pn := []int{2, 3, 7, 11, 13, 17, 19, 23, 27, 31}
+
+       q := make(chan int, nwork*3)
+       r := make(chan int, nwork*3)
+
+       // workers
+       var wg sync.WaitGroup
+       for i := 0; i < nwork; i++ {
+               wg.Add(1)
+               go func(w int) {
+                       for v := range q {
+                               // mess with the fifo-ish nature of range
+                               if pn[w%len(pn)] == v {
+                                       runtime.Gosched()
+                               }
+                               r <- v
+                       }
+                       wg.Done()
+               }(i)
+       }
+
+       // feeder & closer
+       expect := 0
+       go func() {
+               for i := 0; i < niter; i++ {
+                       v := pn[i%len(pn)]
+                       expect += v
+                       q <- v
+               }
+               close(q)  // no more work
+               wg.Wait() // workers done
+               close(r)  // ... so there can be no more results
+       }()
+
+       // consume & check
+       n := 0
+       s := 0
+       for v := range r {
+               n++
+               s += v
+       }
+       if n != niter || s != expect {
+               t.Errorf("Expected sum %d (got %d) from %d iter (saw %d)",
+                       expect, s, niter, n)
+       }
+}
+
 func BenchmarkSelectUncontended(b *testing.B) {
        const CallsPerSched = 1000
        procs := runtime.GOMAXPROCS(-1)