runtime: improve scheduler fairness
Currently global runqueue is starved if a group of goroutines
constantly respawn each other (local runqueue never becomes empty).
Fixes #5639.
R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/10042044
diff --git a/src/pkg/runtime/proc_test.go b/src/pkg/runtime/proc_test.go
index 21fb9c2..83368e0 100644
--- a/src/pkg/runtime/proc_test.go
+++ b/src/pkg/runtime/proc_test.go
@@ -8,6 +8,7 @@
"math"
"runtime"
"sync/atomic"
+ "syscall"
"testing"
"time"
)
@@ -107,6 +108,55 @@
}
}
+func TestTimerFairness(t *testing.T) {
+ done := make(chan bool)
+ c := make(chan bool)
+ for i := 0; i < 2; i++ {
+ go func() {
+ for {
+ select {
+ case c <- true:
+ case <-done:
+ return
+ }
+ }
+ }()
+ }
+
+ timer := time.After(20 * time.Millisecond)
+ for {
+ select {
+ case <-c:
+ case <-timer:
+ close(done)
+ return
+ }
+ }
+}
+
+func TestTimerFairness2(t *testing.T) {
+ done := make(chan bool)
+ c := make(chan bool)
+ for i := 0; i < 2; i++ {
+ go func() {
+ timer := time.After(20 * time.Millisecond)
+ var buf [1]byte
+ for {
+ syscall.Read(0, buf[0:0])
+ select {
+ case c <- true:
+ case <-c:
+ case <-timer:
+ done <- true
+ return
+ }
+ }
+ }()
+ }
+ <-done
+ <-done
+}
+
func stackGrowthRecursive(i int) {
var pad [128]uint64
if i != 0 && pad[0] == 0 {
