pkg/testutil: ForceGosched -> WaitSchedule

ForceGosched() performs bad when GOMAXPROCS>1. When GOMAXPROCS=1, it
could promise that other goroutines run long enough
because it always yield the processor to other goroutines. But it cannot
yield processor to goroutine running on other processors. So when
GOMAXPROCS>1, the yield may finish when goroutine on the other
processor just runs for little time.

Here is a test to confirm the case:

```
package main

import (
	"fmt"
	"runtime"
	"testing"
)

func ForceGosched() {
	// possibility enough to sched up to 10 go routines.
	for i := 0; i < 10000; i++ {
		runtime.Gosched()
	}
}

var d int

func loop(c chan struct{}) {
	for {
		select {
		case <-c:
			for i := 0; i < 1000; i++ {
				fmt.Sprintf("come to time %d", i)
			}
			d++
		}
	}
}

func TestLoop(t *testing.T) {
	c := make(chan struct{}, 1)
	go loop(c)
	c <- struct{}{}
	ForceGosched()
	if d != 1 {
		t.Fatal("d is not incremented")
	}
}
```

`go test -v -race` runs well, but `GOMAXPROCS=2 go test -v -race` fails.

Change the functionality to waiting for schedule to happen.

etcdserver/server_test.go

@@ -607,7 +607,7 @@ func TestSync(t *testing.T) {
 	})
 	srv.sync(10 * time.Second)
 	timer.Stop()
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 
 	action := n.Action()
 	if len(action) != 1 {
@@ -642,7 +642,7 @@ func TestSyncTimeout(t *testing.T) {
 	timer.Stop()
 
 	// give time for goroutine in sync to cancel
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	w := []testutil.Action{{Name: "Propose blocked"}}
 	if g := n.Action(); !reflect.DeepEqual(g, w) {
 		t.Errorf("action = %v, want %v", g, w)
@@ -676,7 +676,7 @@ func TestSyncTrigger(t *testing.T) {
 	}
 	// trigger a sync request
 	st <- time.Time{}
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 
 	action := n.Action()
 	if len(action) != 1 {
@@ -710,7 +710,7 @@ func TestSnapshot(t *testing.T) {
 		store: st,
 	}
 	srv.snapshot(1, raftpb.ConfState{Nodes: []uint64{1}})
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	gaction := st.Action()
 	if len(gaction) != 2 {
 		t.Fatalf("len(action) = %d, want 1", len(gaction))
@@ -786,7 +786,7 @@ func TestRecvSnapshot(t *testing.T) {
 	s.start()
 	n.readyc <- raft.Ready{Snapshot: raftpb.Snapshot{Metadata: raftpb.SnapshotMetadata{Index: 1}}}
 	// make goroutines move forward to receive snapshot
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	s.Stop()
 
 	wactions := []testutil.Action{{Name: "Recovery"}}
@@ -827,7 +827,7 @@ func TestApplySnapshotAndCommittedEntries(t *testing.T) {
 		},
 	}
 	// make goroutines move forward to receive snapshot
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	s.Stop()
 
 	actions := st.Action()

pkg/testutil/testutil.go

@@ -16,17 +16,13 @@ package testutil
 
 import (
 	"net/url"
-	"runtime"
 	"testing"
+	"time"
 )
 
-// WARNING: This is a hack.
-// Remove this when we are able to block/check the status of the go-routines.
-func ForceGosched() {
-	// possibility enough to sched up to 10 go routines.
-	for i := 0; i < 10000; i++ {
-		runtime.Gosched()
-	}
+// TODO: improve this when we are able to know the schedule or status of target go-routine.
+func WaitSchedule() {
+	time.Sleep(3 * time.Millisecond)
 }
 
 func MustNewURLs(t *testing.T, urls []string) []url.URL {

raft/node_test.go

@@ -199,7 +199,7 @@ func TestBlockProposal(t *testing.T) {
 		errc <- n.Propose(context.TODO(), []byte("somedata"))
 	}()
 
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	select {
 	case err := <-errc:
 		t.Errorf("err = %v, want blocking", err)
@@ -207,7 +207,7 @@ func TestBlockProposal(t *testing.T) {
 	}
 
 	n.Campaign(context.TODO())
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	select {
 	case err := <-errc:
 		if err != nil {

rafthttp/pipeline_test.go

@@ -39,7 +39,7 @@ func TestPipelineSend(t *testing.T) {
 	p := newPipeline(tr, picker, types.ID(2), types.ID(1), types.ID(1), fs, &fakeRaft{}, nil)
 
 	p.msgc <- raftpb.Message{Type: raftpb.MsgApp}
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	p.stop()
 
 	if tr.Request() == nil {
@@ -60,7 +60,7 @@ func TestPipelineExceedMaximalServing(t *testing.T) {
 
 	// keep the sender busy and make the buffer full
 	// nothing can go out as we block the sender
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	for i := 0; i < connPerPipeline+pipelineBufSize; i++ {
 		select {
 		case p.msgc <- raftpb.Message{}:
@@ -68,7 +68,7 @@ func TestPipelineExceedMaximalServing(t *testing.T) {
 			t.Errorf("failed to send out message")
 		}
 		// force the sender to grab data
-		testutil.ForceGosched()
+		testutil.WaitSchedule()
 	}
 
 	// try to send a data when we are sure the buffer is full
@@ -80,7 +80,7 @@ func TestPipelineExceedMaximalServing(t *testing.T) {
 
 	// unblock the senders and force them to send out the data
 	tr.unblock()
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 
 	// It could send new data after previous ones succeed
 	select {
@@ -99,7 +99,7 @@ func TestPipelineSendFailed(t *testing.T) {
 	p := newPipeline(newRespRoundTripper(0, errors.New("blah")), picker, types.ID(2), types.ID(1), types.ID(1), fs, &fakeRaft{}, nil)
 
 	p.msgc <- raftpb.Message{Type: raftpb.MsgApp}
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	p.stop()
 
 	fs.Lock()

rafthttp/stream_test.go

@@ -33,7 +33,7 @@ func TestStreamWriterAttachOutgoingConn(t *testing.T) {
 		prevwfc := wfc
 		wfc = &fakeWriteFlushCloser{}
 		sw.attach(&outgoingConn{t: streamTypeMessage, Writer: wfc, Flusher: wfc, Closer: wfc})
-		testutil.ForceGosched()
+		testutil.WaitSchedule()
 		// previous attached connection should be closed
 		if prevwfc != nil && prevwfc.closed != true {
 			t.Errorf("#%d: close of previous connection = %v, want true", i, prevwfc.closed)
@@ -44,7 +44,7 @@ func TestStreamWriterAttachOutgoingConn(t *testing.T) {
 		}
 
 		sw.msgc <- raftpb.Message{}
-		testutil.ForceGosched()
+		testutil.WaitSchedule()
 		// still working
 		if _, ok := sw.writec(); ok != true {
 			t.Errorf("#%d: working status = %v, want true", i, ok)
@@ -73,7 +73,7 @@ func TestStreamWriterAttachBadOutgoingConn(t *testing.T) {
 	sw.attach(&outgoingConn{t: streamTypeMessage, Writer: wfc, Flusher: wfc, Closer: wfc})
 
 	sw.msgc <- raftpb.Message{}
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	// no longer working
 	if _, ok := sw.writec(); ok != false {
 		t.Errorf("working = %v, want false", ok)

rafthttp/transport_test.go

@@ -137,7 +137,7 @@ func TestTransportErrorc(t *testing.T) {
 	}
 	tr.peers[1].Send(raftpb.Message{})
 
-	testutil.ForceGosched()
+	testutil.WaitSchedule()
 	select {
 	case <-errorc:
 	default: