runtime: fix deadlock in parallel for test

The deadlock occurs when another goroutine requests GC
during the test. When wait=true the test expects physical parallelism,
that is, that P goroutines are all active at the same time.
If GC is requested, then part of the goroutines are not scheduled,
so other goroutines deadlock.
With wait=false, goroutines finish parallel for w/o waiting for all
other goroutines.
Fixes #3954.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6820098

diff --git a/src/pkg/runtime/parfor_test.go b/src/pkg/runtime/parfor_test.go
index 7644354ab36af3a85c7df34d44087560693a7023..b382b76a7b2b687e642310298dc94d46e87e696e 100644 (file)
--- a/src/pkg/runtime/parfor_test.go
+++ b/src/pkg/runtime/parfor_test.go
@@ -109,14 +109,21 @@ func TestParForParallel(t *testing.T) {
                data[i] = i
        }
        P := GOMAXPROCS(-1)
+       c := make(chan bool, P)
        desc := NewParFor(uint32(P))
-       ParForSetup(desc, uint32(P), uint32(N), nil, true, func(desc *ParFor, i uint32) {
+       ParForSetup(desc, uint32(P), uint32(N), nil, false, func(desc *ParFor, i uint32) {
                data[i] = data[i]*data[i] + 1
        })
        for p := 1; p < P; p++ {
-               go ParForDo(desc)
+               go func() {
+                       ParForDo(desc)
+                       c <- true
+               }()
        }
        ParForDo(desc)
+       for p := 1; p < P; p++ {
+               <-c
+       }
        for i := uint64(0); i < N; i++ {
                if data[i] != i*i+1 {
                        t.Fatalf("Wrong element %d: %d", i, data[i])