[#166] node: Parallelize background tree service sync by batching

* Merge operations

Signed-off-by: Airat Arifullin a.arifullin@yadro.com

pkg/services/tree/sync_test.go

@@ -0,0 +1,85 @@
+package tree
+
+import (
+	"context"
+	"testing"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/pilorama"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_mergeOperationStreams(t *testing.T) {
+	tests := []struct {
+		name          string
+		ctx           context.Context
+		opTimes       [][]uint64
+		wantValues    []uint64
+		wantMinHeight uint64
+	}{
+		{
+			name: "1",
+			ctx:  context.Background(),
+			opTimes: [][]uint64{
+				{250, 251, 255},
+				{252, 253, 254, 256, 257},
+			},
+			wantValues:    []uint64{250, 251, 252, 253, 254, 255, 256, 257},
+			wantMinHeight: 255,
+		},
+		{
+			name: "2",
+			ctx:  context.Background(),
+			opTimes: [][]uint64{
+				{250, 251, 255, 259},
+				{252, 253, 254, 256, 257},
+			},
+			wantValues:    []uint64{250, 251, 252, 253, 254, 255, 256, 257, 259},
+			wantMinHeight: 257,
+		},
+		{
+			name: "3",
+			ctx:  context.Background(),
+			opTimes: [][]uint64{
+				{250, 251, 255},
+				{249, 250, 251, 253, 254, 256, 257},
+			},
+			wantValues:    []uint64{249, 250, 250, 251, 251, 253, 254, 255, 256, 257},
+			wantMinHeight: 255,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nodeOpChans := make([]chan *pilorama.Move, len(tt.opTimes))
+			for i := range nodeOpChans {
+				nodeOpChans[i] = make(chan *pilorama.Move)
+			}
+
+			// generate and put values to all chans
+			for i, ch := range nodeOpChans {
+				i := i
+				ch := ch
+				go func() {
+					for _, tm := range tt.opTimes[i] {
+						op := &pilorama.Move{}
+						op.Time = tm
+						ch <- op
+					}
+					close(nodeOpChans[i])
+				}()
+			}
+
+			merged := make(chan *pilorama.Move, 1)
+			min := make(chan uint64)
+			go func() {
+				min <- mergeOperationStreams(tt.ctx, nodeOpChans, merged)
+			}()
+
+			var res []uint64
+			for op := range merged {
+				res = append(res, op.Time)
+			}
+			require.Equal(t, tt.wantValues, res)
+			require.Equal(t, tt.wantMinHeight, <-min)
+		})
+	}
+}