runtime: ensure fair scheduling during frequent GCs
What was happenning is as follows:
Each writer goroutine always triggers GC during its scheduling quntum.
After GC goroutines are shuffled so that the timer goroutine is always second in the queue.
This repeats infinitely, causing timer goroutine starvation.
Fixes #7126.
R=golang-codereviews, shanemhansen, khr, khr
CC=golang-codereviews
https://golang.org/cl/53080043
diff --git a/src/pkg/runtime/proc_test.go b/src/pkg/runtime/proc_test.go
index dd70ed9..d3f1f8b 100644
--- a/src/pkg/runtime/proc_test.go
+++ b/src/pkg/runtime/proc_test.go
@@ -244,6 +244,49 @@
atomic.StoreUint32(&stop, 1)
}
+func TestGCFairness(t *testing.T) {
+ output := executeTest(t, testGCFairnessSource, nil)
+ want := "OK\n"
+ if output != want {
+ t.Fatalf("want %s, got %s\n", want, output)
+ }
+}
+
+const testGCFairnessSource = `
+package main
+
+import (
+ "fmt"
+ "os"
+ "runtime"
+ "time"
+)
+
+func main() {
+ runtime.GOMAXPROCS(1)
+ f, err := os.Open("/dev/null")
+ if os.IsNotExist(err) {
+ // This test tests what it is intended to test only if writes are fast.
+ // If there is no /dev/null, we just don't execute the test.
+ fmt.Println("OK\n")
+ return
+ }
+ if err != nil {
+ fmt.Println(err)
+ os.Exit(1)
+ }
+ for i := 0; i < 2; i++ {
+ go func() {
+ for {
+ f.Write([]byte("."))
+ }
+ }()
+ }
+ time.Sleep(10 * time.Millisecond)
+ fmt.Println("OK")
+}
+`
+
func stackGrowthRecursive(i int) {
var pad [128]uint64
if i != 0 && pad[0] == 0 {
