fix events deadlock when chaining calls

chain/events/events_height.go

@@ -132,9 +132,12 @@ func (e *heightEvents) ChainAt(hnd HeightHandler, rev RevertHandler, confidence
 			log.Warnf("events.ChainAt: calling HandleFunc with nil tipset, not found in cache: %s", err)
 		}
 
+		e.lk.Unlock()
 		if err := hnd(ts, bestH); err != nil {
 			return err
 		}
+		e.lk.Lock()
+		bestH = e.tsc.best().Height()
 	}
 
 	if bestH >= h+uint64(confidence)+e.gcConfidence {

chain/events/events_test.go

@@ -364,6 +364,74 @@ func TestAtStartConfidence(t *testing.T) {
 	require.Equal(t, false, reverted)
 }
 
+func TestAtChained(t *testing.T) {
+	fcs := &fakeCS{
+		t:   t,
+		h:   1,
+		tsc: newTSCache(2*build.ForkLengthThreshold, nil),
+	}
+	require.NoError(t, fcs.tsc.add(makeTs(t, 1, dummyCid)))
+
+	events := NewEvents(context.Background(), fcs)
+
+	var applied bool
+	var reverted bool
+
+	err := events.ChainAt(func(ts *types.TipSet, curH uint64) error {
+		return events.ChainAt(func(ts *types.TipSet, curH uint64) error {
+			require.Equal(t, 10, int(ts.Height()))
+			applied = true
+			return nil
+		}, func(ts *types.TipSet) error {
+			reverted = true
+			return nil
+		}, 3, 10)
+	}, func(ts *types.TipSet) error {
+		reverted = true
+		return nil
+	}, 3, 5)
+	require.NoError(t, err)
+
+	fcs.advance(0, 15, nil)
+
+	require.Equal(t, true, applied)
+	require.Equal(t, false, reverted)
+}
+
+func TestAtChainedConfidence(t *testing.T) {
+	fcs := &fakeCS{
+		t:   t,
+		h:   1,
+		tsc: newTSCache(2*build.ForkLengthThreshold, nil),
+	}
+	require.NoError(t, fcs.tsc.add(makeTs(t, 1, dummyCid)))
+
+	events := NewEvents(context.Background(), fcs)
+
+	fcs.advance(0, 15, nil)
+
+	var applied bool
+	var reverted bool
+
+	err := events.ChainAt(func(ts *types.TipSet, curH uint64) error {
+		return events.ChainAt(func(ts *types.TipSet, curH uint64) error {
+			require.Equal(t, 10, int(ts.Height()))
+			applied = true
+			return nil
+		}, func(ts *types.TipSet) error {
+			reverted = true
+			return nil
+		}, 3, 10)
+	}, func(ts *types.TipSet) error {
+		reverted = true
+		return nil
+	}, 3, 5)
+	require.NoError(t, err)
+
+	require.Equal(t, true, applied)
+	require.Equal(t, false, reverted)
+}
+
 func TestCalled(t *testing.T) {
 	fcs := &fakeCS{
 		t: t,