feature(worker): ability to hot reload mirror job configrations, close #18

worker/config_diff.go

@@ -0,0 +1,88 @@
+package worker
+
+import (
+	"fmt"
+	"reflect"
+	"sort"
+)
+
+// Find difference of mirror config, this is important for hot reloading config file
+// NOTICE: only the [[mirrors]] section is supported
+
+// make []mirrorConfig sortable
+type sortableMirrorList []mirrorConfig
+
+func (l sortableMirrorList) Len() int           { return len(l) }
+func (l sortableMirrorList) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
+func (l sortableMirrorList) Less(i, j int) bool { return l[i].Name < l[j].Name }
+
+const (
+	diffDelete uint8 = iota
+	diffAdd
+	diffModify
+)
+
+// a unit of mirror config difference
+type mirrorCfgTrans struct {
+	diffOp uint8
+	mirCfg mirrorConfig
+}
+
+func (t mirrorCfgTrans) String() string {
+	var op string
+	if t.diffOp == diffDelete {
+		op = "Del"
+	} else {
+		op = "Add"
+	}
+	return fmt.Sprintf("{%s, %s}", op, t.mirCfg.Name)
+}
+
+// diffMirrorConfig finds the difference between the oldList and the newList
+// it returns a series of operations that if these operations are applied to
+// oldList, a newList equavuilance can be obtained.
+func diffMirrorConfig(oldList, newList []mirrorConfig) []mirrorCfgTrans {
+	operations := []mirrorCfgTrans{}
+
+	oList := make([]mirrorConfig, len(oldList))
+	nList := make([]mirrorConfig, len(newList))
+	copy(oList, oldList)
+	copy(nList, newList)
+
+	// first ensure oldList and newList are sorted
+	sort.Sort(sortableMirrorList(oList))
+	sort.Sort(sortableMirrorList(nList))
+
+	// insert a tail node to both lists
+	// as the maximum node
+	lastOld, lastNew := oList[len(oList)-1], nList[len(nList)-1]
+	maxName := lastOld.Name
+	if lastNew.Name > lastOld.Name {
+		maxName = lastNew.Name
+	}
+	Nil := mirrorConfig{Name: "~" + maxName}
+	if Nil.Name <= maxName {
+		panic("Nil.Name should be larger than maxName")
+	}
+	oList, nList = append(oList, Nil), append(nList, Nil)
+
+	// iterate over both lists to find the difference
+	for i, j := 0, 0; i < len(oList) && j < len(nList); {
+		o, n := oList[i], nList[j]
+		if n.Name < o.Name {
+			operations = append(operations, mirrorCfgTrans{diffAdd, n})
+			j++
+		} else if o.Name < n.Name {
+			operations = append(operations, mirrorCfgTrans{diffDelete, o})
+			i++
+		} else {
+			if !reflect.DeepEqual(o, n) {
+				operations = append(operations, mirrorCfgTrans{diffModify, n})
+			}
+			i++
+			j++
+		}
+	}
+
+	return operations
+}