Support failover in cluster (experimental)

cluster/core/cron.go

@@ -0,0 +1,36 @@
+package core
+
+import (
+	"sync/atomic"
+	"time"
+
+	"github.com/hdt3213/godis/cluster/raft"
+)
+
+func (cluster *Cluster) clusterCron() {
+	if cluster.config.noCron {
+		return
+	}
+	ticker := time.NewTicker(time.Second)
+	var running int32
+	for {
+		select {
+		case <-ticker.C:
+			if cluster.raftNode.State() == raft.Leader {
+				if atomic.CompareAndSwapInt32(&running, 0, 1) {
+					// Disable parallelism
+					go func() {
+						cluster.doFailoverCheck()
+						cluster.doRebalance()
+						atomic.StoreInt32(&running, 0)
+					}()
+				}
+			} else {
+				cluster.sendHearbeat()
+			}
+		case <-cluster.closeChan:
+			ticker.Stop()
+			return
+		}
+	}
+}