server: add Uptime status counter

server/server.go

@@ -87,6 +87,7 @@ type Server struct {
 	concurrentLimiter *TokenLimiter
 	clients           map[uint32]*clientConn
 	capability        uint32
+	startTime         time.Time
 
 	// stopListenerCh is used when a critical error occurred, we don't want to exit the process, because there may be
 	// a supervisor automatically restart it, then new client connection will be created, but we can't server it.
@@ -178,6 +179,7 @@ func NewServer(cfg *config.Config, driver IDriver) (*Server, error) {
 		rwlock:            &sync.RWMutex{},
 		clients:           make(map[uint32]*clientConn),
 		stopListenerCh:    make(chan struct{}, 1),
+		startTime:         time.Now(),
 	}
 	s.loadTLSCertificates()
 
@@ -222,6 +224,8 @@ func NewServer(cfg *config.Config, driver IDriver) (*Server, error) {
 		return nil, errors.Trace(err)
 	}
 
+	variable.RegisterStatistics(s)
+
 	// Init rand seed for randomBuf()
 	rand.Seed(time.Now().UTC().UnixNano())
 	return s, nil

server/stat.go

@@ -0,0 +1,37 @@
+// Copyright 2018 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"time"
+
+	"github.com/pingcap/tidb/sessionctx/variable"
+)
+
+var (
+	uptime = "Uptime"
+)
+
+// GetScope gets the status variables scope.
+func (s *Server) GetScope(status string) variable.ScopeFlag {
+	// Now server status variables scope are all default scope.
+	return variable.DefaultStatusVarScopeFlag
+}
+
+// Stats returns the server statistics.
+func (s *Server) Stats(vars *variable.SessionVars) (map[string]interface{}, error) {
+	m := make(map[string]interface{})
+	m[uptime] = int(time.Since(s.startTime).Seconds())
+	return m, nil
+}