func (s *MongoSuite) dialAndTestInitiate(c *gc.C, inst *gitjujutesting.MgoInstance, addr string) {
	session := inst.MustDialDirect()
	defer session.Close()

	mode := session.Mode()
	err := Initiate(session, addr, rsName, initialTags)
	c.Assert(err, gc.IsNil)

	// make sure we haven't messed with the session's mode
	c.Assert(session.Mode(), gc.Equals, mode)

	// Ids start at 1 for us, so we can differentiate between set and unset
	expectedMembers := []Member{Member{Id: 1, Address: addr, Tags: initialTags}}

	// need to set mode to strong so that we wait for the write to succeed
	// before reading and thus ensure that we're getting consistent reads.
	session.SetMode(mgo.Strong, false)

	mems, err := CurrentMembers(session)
	c.Assert(err, gc.IsNil)
	c.Assert(mems, jc.DeepEquals, expectedMembers)

	// now add some data so we get a more real-life test
	loadData(session, c)
}

func (s *oplogSuite) startMongo(c *gc.C) (*jujutesting.MgoInstance, *mgo.Session) {
	var inst jujutesting.MgoInstance
	err := inst.Start(nil)
	c.Assert(err, jc.ErrorIsNil)
	s.AddCleanup(func(*gc.C) { inst.Destroy() })
	return &inst, s.dialMongo(c, &inst)
}

func (s *oplogSuite) dialMongo(c *gc.C, inst *jujutesting.MgoInstance) *mgo.Session {
	session, err := inst.Dial()
	c.Assert(err, jc.ErrorIsNil)
	s.AddCleanup(func(*gc.C) { session.Close() })
	return session
}

func (s *mongoSuite) testStateWorkerDialSetsWriteMajority(c *gc.C, configureReplset bool) {
	inst := gitjujutesting.MgoInstance{
		Params: []string{"--replSet", "juju"},
	}
	err := inst.Start(coretesting.Certs)
	c.Assert(err, jc.ErrorIsNil)
	defer inst.Destroy()

	var expectedWMode string
	dialOpts := stateWorkerDialOpts
	dialOpts.Timeout = coretesting.LongWait
	if configureReplset {
		info := inst.DialInfo()
		info.Timeout = dialOpts.Timeout
		args := peergrouper.InitiateMongoParams{
			DialInfo:       info,
			MemberHostPort: inst.Addr(),
		}
		err = peergrouper.InitiateMongoServer(args)
		c.Assert(err, jc.ErrorIsNil)
		expectedWMode = "majority"
	} else {
		dialOpts.Direct = true
	}

	mongoInfo := mongo.Info{
		Addrs:  []string{inst.Addr()},
		CACert: coretesting.CACert,
	}
	session, err := mongo.DialWithInfo(mongoInfo, dialOpts)
	c.Assert(err, jc.ErrorIsNil)
	defer session.Close()

	safe := session.Safe()
	c.Assert(safe, gc.NotNil)
	c.Assert(safe.WMode, gc.Equals, expectedWMode)
	c.Assert(safe.J, jc.IsTrue) // always enabled
}

func (s *MongoSuite) assertAddRemoveSet(c *gc.C, root *gitjujutesting.MgoInstance, getAddr func(*gitjujutesting.MgoInstance) string) {
	session := root.MustDial()
	defer session.Close()

	members := make([]Member, 0, 5)

	// Add should be idempotent, so re-adding root here shouldn't result in
	// two copies of root in the replica set
	members = append(members, Member{Address: getAddr(root), Tags: initialTags})

	instances := make([]*gitjujutesting.MgoInstance, 5)
	instances[0] = root
	for i := 1; i < len(instances); i++ {
		inst := newServer(c)
		instances[i] = inst
		defer inst.Destroy()
		defer func() {
			err := Remove(session, getAddr(inst))
			c.Assert(err, gc.IsNil)
		}()
		key := fmt.Sprintf("key%d", i)
		val := fmt.Sprintf("val%d", i)
		tags := map[string]string{key: val}
		members = append(members, Member{Address: getAddr(inst), Tags: tags})
	}

	// We allow for up to 2m per operation, since Add, Set, etc. call
	// replSetReconfig which may cause primary renegotiation. According
	// to the Mongo docs, "typically this is 10-20 seconds, but could be
	// as long as a minute or more."
	//
	// Note that the delay is set at 500ms to cater for relatively quick
	// operations without thrashing on those that take longer.
	strategy := utils.AttemptStrategy{Total: time.Minute * 2, Delay: time.Millisecond * 500}
	attemptLoop(c, strategy, "Add()", func() error {
		return Add(session, members...)
	})

	expectedMembers := make([]Member, len(members))
	for i, m := range members {
		// Ids should start at 1 (for the root) and go up
		m.Id = i + 1
		expectedMembers[i] = m
	}

	var cfg *Config
	attemptLoop(c, strategy, "CurrentConfig()", func() error {
		var err error
		cfg, err = CurrentConfig(session)
		return err
	})
	c.Assert(cfg.Name, gc.Equals, rsName)
	// 2 since we already changed it once
	c.Assert(cfg.Version, gc.Equals, 2)

	mems := cfg.Members
	c.Assert(mems, jc.DeepEquals, expectedMembers)

	// Now remove the last two Members...
	attemptLoop(c, strategy, "Remove()", func() error {
		return Remove(session, members[3].Address, members[4].Address)
	})
	expectedMembers = expectedMembers[0:3]

	// ... and confirm that CurrentMembers reflects the removal.
	attemptLoop(c, strategy, "CurrentMembers()", func() error {
		var err error
		mems, err = CurrentMembers(session)
		return err
	})
	c.Assert(mems, jc.DeepEquals, expectedMembers)

	// now let's mix it up and set the new members to a mix of the previous
	// plus the new arbiter
	mems = []Member{members[3], mems[2], mems[0], members[4]}
	attemptLoop(c, strategy, "Set()", func() error {
		err := Set(session, mems)
		if err != nil {
			c.Logf("current session mode: %v", session.Mode())
			session.Refresh()
		}
		return err
	})

	attemptLoop(c, strategy, "Ping()", func() error {
		// can dial whichever replica address here, mongo will figure it out
		if session != nil {
			session.Close()
		}
		session = instances[0].MustDialDirect()
		return session.Ping()
	})

	// any new members will get an id of max(other_ids...)+1
	expectedMembers = []Member{members[3], expectedMembers[2], expectedMembers[0], members[4]}
	expectedMembers[0].Id = 4
	expectedMembers[3].Id = 5

	attemptLoop(c, strategy, "CurrentMembers()", func() error {
		var err error
//.........这里部分代码省略.........