fs/accounting: add option to delete stats

Removed PruneAllTransfers because it had no use. startedTransfers are
set to nil in ResetCounters.

fs/accounting/stats_groups_test.go

@@ -0,0 +1,104 @@
+package accounting
+
+import (
+	"fmt"
+	"runtime"
+	"testing"
+)
+
+func TestStatsGroupOperations(t *testing.T) {
+
+	t.Run("empty group returns nil", func(t *testing.T) {
+		t.Parallel()
+		sg := newStatsGroups()
+		sg.get("invalid-group")
+	})
+
+	t.Run("set assigns stats to group", func(t *testing.T) {
+		t.Parallel()
+		stats := NewStats()
+		sg := newStatsGroups()
+		sg.set("test", stats)
+		sg.set("test1", stats)
+		if len(sg.m) != len(sg.names()) || len(sg.m) != 2 {
+			t.Fatalf("Expected two stats got %d, %d", len(sg.m), len(sg.order))
+		}
+	})
+
+	t.Run("get returns correct group", func(t *testing.T) {
+		t.Parallel()
+		stats := NewStats()
+		sg := newStatsGroups()
+		sg.set("test", stats)
+		sg.set("test1", stats)
+		got := sg.get("test")
+		if got != stats {
+			t.Fatal("get returns incorrect stats")
+		}
+	})
+
+	t.Run("sum returns correct values", func(t *testing.T) {
+		t.Parallel()
+		stats1 := NewStats()
+		stats1.bytes = 5
+		stats1.errors = 5
+		stats2 := NewStats()
+		sg := newStatsGroups()
+		sg.set("test1", stats1)
+		sg.set("test2", stats2)
+		sum := sg.sum()
+		if sum.bytes != stats1.bytes+stats2.bytes {
+			t.Fatalf("sum() => bytes %d, expected %d", sum.bytes, stats1.bytes+stats2.bytes)
+		}
+		if sum.errors != stats1.errors+stats2.errors {
+			t.Fatalf("sum() => errors %d, expected %d", sum.errors, stats1.errors+stats2.errors)
+		}
+	})
+
+	t.Run("delete removes stats", func(t *testing.T) {
+		t.Parallel()
+		stats := NewStats()
+		sg := newStatsGroups()
+		sg.set("test", stats)
+		sg.set("test1", stats)
+		sg.delete("test1")
+		if sg.get("test1") != nil {
+			t.Fatal("stats not deleted")
+		}
+		if len(sg.m) != len(sg.names()) || len(sg.m) != 1 {
+			t.Fatalf("Expected two stats got %d, %d", len(sg.m), len(sg.order))
+		}
+	})
+
+	t.Run("memory is reclaimed", func(t *testing.T) {
+		var (
+			count      = 1000
+			start, end runtime.MemStats
+			sg         = newStatsGroups()
+		)
+
+		runtime.GC()
+		runtime.ReadMemStats(&start)
+
+		for i := 0; i < count; i++ {
+			sg.set(fmt.Sprintf("test-%d", i), NewStats())
+		}
+
+		for i := 0; i < count; i++ {
+			sg.delete(fmt.Sprintf("test-%d", i))
+		}
+
+		runtime.GC()
+		runtime.ReadMemStats(&end)
+
+		t.Log(fmt.Sprintf("%+v\n%+v", start, end))
+		diff := percentDiff(start.HeapObjects, end.HeapObjects)
+		if diff > 1 || diff < 0 {
+			t.Errorf("HeapObjects = %d, expected %d", end.HeapObjects, start.HeapObjects)
+		}
+	})
+}
+
+func percentDiff(start, end uint64) uint64 {
+	return (start - end) * 100 / start
+}