client/sd: unify the service discovery callbacks within a struct

client/clients/tso/client.go

@@ -116,9 +116,8 @@ func NewClient(
 		},
 	}
 
-	eventSrc := svcDiscovery.(sd.TSOEventSource)
-	eventSrc.SetTSOLeaderURLUpdatedCallback(c.updateTSOLeaderURL)
-	c.svcDiscovery.AddServiceURLsSwitchedCallback(c.scheduleUpdateTSOConnectionCtxs)
+	c.svcDiscovery.ExecAndAddLeaderSwitchedCallback(c.updateTSOLeaderURL)
+	c.svcDiscovery.AddMembersChangedCallback(c.scheduleUpdateTSOConnectionCtxs)
 
 	return c
 }

client/inner_client.go

@@ -143,11 +143,12 @@ func (c *innerClient) resetTSOClientLocked(mode pdpb.ServiceMode) {
 	}
 }
 
-func (c *innerClient) scheduleUpdateTokenConnection() {
+func (c *innerClient) scheduleUpdateTokenConnection(string) error {
 	select {
 	case c.updateTokenConnectionCh <- struct{}{}:
 	default:
 	}
+	return nil
 }
 
 func (c *innerClient) getServiceMode() pdpb.ServiceMode {
@@ -188,7 +189,7 @@ func (c *innerClient) setup() error {
 	}
 
 	// Register callbacks
-	c.serviceDiscovery.AddServingURLSwitchedCallback(c.scheduleUpdateTokenConnection)
+	c.serviceDiscovery.AddLeaderSwitchedCallback(c.scheduleUpdateTokenConnection)
 
 	// Create dispatchers
 	c.createTokenDispatcher()

client/servicediscovery/callbacks.go

@@ -0,0 +1,104 @@
+// Copyright 2025 TiKV Project Authors.
+//
+// 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package servicediscovery
+
+import (
+	"sync"
+
+	"github.com/pingcap/kvproto/pkg/pdpb"
+)
+
+type leaderSwitchedCallbackFunc func(string) error
+
+// serviceCallbacks contains all the callback functions for service discovery events
+type serviceCallbacks struct {
+	sync.RWMutex
+	// serviceModeUpdateCb will be called when the service mode gets updated
+	serviceModeUpdateCb func(pdpb.ServiceMode)
+	// leaderSwitchedCbs will be called after the leader switched
+	leaderSwitchedCbs []leaderSwitchedCallbackFunc
+	// membersChangedCbs will be called after there is any membership change in the
+	// leader and followers
+	membersChangedCbs []func()
+}
+
+func newServiceCallbacks() *serviceCallbacks {
+	return &serviceCallbacks{
+		leaderSwitchedCbs: make([]leaderSwitchedCallbackFunc, 0),
+		membersChangedCbs: make([]func(), 0),
+	}
+}
+
+func (c *serviceCallbacks) setServiceModeUpdateCallback(cb func(pdpb.ServiceMode)) {
+	c.Lock()
+	defer c.Unlock()
+	c.serviceModeUpdateCb = cb
+}
+
+func (c *serviceCallbacks) addLeaderSwitchedCallback(cb leaderSwitchedCallbackFunc) {
+	c.Lock()
+	defer c.Unlock()
+	c.leaderSwitchedCbs = append(c.leaderSwitchedCbs, cb)
+}
+
+func (c *serviceCallbacks) addMembersChangedCallback(cb func()) {
+	c.Lock()
+	defer c.Unlock()
+	c.membersChangedCbs = append(c.membersChangedCbs, cb)
+}
+
+func (c *serviceCallbacks) onServiceModeUpdate(mode pdpb.ServiceMode) {
+	c.RLock()
+	cb := c.serviceModeUpdateCb
+	c.RUnlock()
+
+	if cb == nil {
+		return
+	}
+	cb(mode)
+}
+
+func (c *serviceCallbacks) onLeaderSwitched(leader string) error {
+	c.RLock()
+	cbs := make([]leaderSwitchedCallbackFunc, len(c.leaderSwitchedCbs))
+	copy(cbs, c.leaderSwitchedCbs)
+	c.RUnlock()
+
+	var err error
+	for _, cb := range cbs {
+		if cb == nil {
+			continue
+		}
+		err = cb(leader)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (c *serviceCallbacks) onMembersChanged() {
+	c.RLock()
+	cbs := make([]func(), len(c.membersChangedCbs))
+	copy(cbs, c.membersChangedCbs)
+	c.RUnlock()
+
+	for _, cb := range cbs {
+		if cb == nil {
+			continue
+		}
+		cb()
+	}
+}

client/servicediscovery/mock_service_discovery.go

@@ -100,8 +100,11 @@
 // CheckMemberChanged implements the ServiceDiscovery interface.
 func (*mockServiceDiscovery) CheckMemberChanged() error { return nil }
 
-// AddServingURLSwitchedCallback implements the ServiceDiscovery interface.
-func (*mockServiceDiscovery) AddServingURLSwitchedCallback(...func()) {}
+// ExecAndAddLeaderSwitchedCallback implements the ServiceDiscovery interface.
+func (*mockServiceDiscovery) ExecAndAddLeaderSwitchedCallback(leaderSwitchedCallbackFunc) {}
 
-// AddServiceURLsSwitchedCallback implements the ServiceDiscovery interface.
-func (*mockServiceDiscovery) AddServiceURLsSwitchedCallback(...func()) {}
+// AddLeaderSwitchedCallback implements the ServiceDiscovery interface.
+func (*mockServiceDiscovery) AddLeaderSwitchedCallback(leaderSwitchedCallbackFunc) {}
+
+// AddMembersChangedCallback implements the ServiceDiscovery interface.
+func (*mockServiceDiscovery) AddMembersChangedCallback(func()) {}

client/servicediscovery/service_discovery.go

@@ -126,14 +126,16 @@
 	// CheckMemberChanged immediately check if there is any membership change among the leader/followers
 	// in a quorum-based cluster or among the primary/secondaries in a primary/secondary configured cluster.
 	CheckMemberChanged() error
-	// AddServingURLSwitchedCallback adds callbacks which will be called when the leader
+	// ExecAndAddLeaderSwitchedCallback executes the callback once and adds it to the callback list then.
+	ExecAndAddLeaderSwitchedCallback(cb leaderSwitchedCallbackFunc)
+	// AddLeaderSwitchedCallback adds callbacks which will be called when the leader
 	// in a quorum-based cluster or the primary in a primary/secondary configured cluster
 	// is switched.
-	AddServingURLSwitchedCallback(callbacks ...func())
-	// AddServiceURLsSwitchedCallback adds callbacks which will be called when any leader/follower
+	AddLeaderSwitchedCallback(cb leaderSwitchedCallbackFunc)
+	// AddMembersChangedCallback adds callbacks which will be called when any leader/follower
 	// in a quorum-based cluster or any primary/secondary in a primary/secondary configured cluster
 	// is changed.
-	AddServiceURLsSwitchedCallback(callbacks ...func())
+	AddMembersChangedCallback(cb func())
 }
 
 // ServiceClient is an interface that defines a set of operations for a raw PD gRPC client to specific PD server.
@@ -394,18 +396,8 @@
 
 // UpdateKeyspaceIDFunc is the function type for updating the keyspace ID.
 type UpdateKeyspaceIDFunc func() error
-type tsoLeaderURLUpdatedFunc func(string) error
 
-// TSOEventSource subscribes to events related to changes in the TSO leader/primary from the service discovery.
-type TSOEventSource interface {
-	// SetTSOLeaderURLUpdatedCallback adds a callback which will be called when the TSO leader/primary is updated.
-	SetTSOLeaderURLUpdatedCallback(callback tsoLeaderURLUpdatedFunc)
-}
-
-var (
-	_ ServiceDiscovery = (*serviceDiscovery)(nil)
-	_ TSOEventSource   = (*serviceDiscovery)(nil)
-)
+var _ ServiceDiscovery = (*serviceDiscovery)(nil)
 
 // serviceDiscovery is the service discovery client of PD/PD service which is quorum based
 type serviceDiscovery struct {
@@ -426,15 +418,7 @@
 	// url -> a gRPC connection
 	clientConns sync.Map // Store as map[string]*grpc.ClientConn
 
-	// serviceModeUpdateCb will be called when the service mode gets updated
-	serviceModeUpdateCb func(pdpb.ServiceMode)
-	// leaderSwitchedCbs will be called after the leader switched
-	leaderSwitchedCbs []func()
-	// membersChangedCbs will be called after there is any membership change in the
-	// leader and followers
-	membersChangedCbs []func()
-	// tsoLeaderUpdatedCb will be called when the TSO leader is updated.
-	tsoLeaderUpdatedCb tsoLeaderURLUpdatedFunc
+	callbacks *serviceCallbacks
 
 	checkMembershipCh chan struct{}
 
@@ -474,12 +458,13 @@
 		cancel:               cancel,
 		wg:                   wg,
 		apiCandidateNodes:    [apiKindCount]*serviceBalancer{newServiceBalancer(emptyErrorFn), newServiceBalancer(regionAPIErrorFn)},
-		serviceModeUpdateCb:  serviceModeUpdateCb,
+		callbacks:            newServiceCallbacks(),
 		updateKeyspaceIDFunc: updateKeyspaceIDFunc,
 		keyspaceID:           keyspaceID,
 		tlsCfg:               tlsCfg,
 		option:               option,
 	}
+	pdsd.callbacks.setServiceModeUpdateCallback(serviceModeUpdateCb)
 	urls = tlsutil.AddrsToURLs(urls, tlsCfg)
 	pdsd.urls.Store(urls)
 	return pdsd
@@ -570,7 +555,7 @@
 		failpoint.Return()
 	})
 	failpoint.Inject("usePDServiceMode", func() {
-		c.serviceModeUpdateCb(pdpb.ServiceMode_PD_SVC_MODE)
+		c.callbacks.onServiceModeUpdate(pdpb.ServiceMode_PD_SVC_MODE)
 		failpoint.Return()
 	})
 
@@ -791,27 +776,29 @@
 	return c.updateMember()
 }
 
-// AddServingURLSwitchedCallback adds callbacks which will be called
-// when the leader is switched.
-func (c *serviceDiscovery) AddServingURLSwitchedCallback(callbacks ...func()) {
-	c.leaderSwitchedCbs = append(c.leaderSwitchedCbs, callbacks...)
-}
-
-// AddServiceURLsSwitchedCallback adds callbacks which will be called when
-// any leader/follower is changed.
-func (c *serviceDiscovery) AddServiceURLsSwitchedCallback(callbacks ...func()) {
-	c.membersChangedCbs = append(c.membersChangedCbs, callbacks...)
-}
-
-// SetTSOLeaderURLUpdatedCallback adds a callback which will be called when the TSO leader is updated.
-func (c *serviceDiscovery) SetTSOLeaderURLUpdatedCallback(callback tsoLeaderURLUpdatedFunc) {
+// ExecAndAddLeaderSwitchedCallback executes the callback once and adds it to the callback list then.
+func (c *serviceDiscovery) ExecAndAddLeaderSwitchedCallback(callback leaderSwitchedCallbackFunc) {
 	url := c.getLeaderURL()
 	if len(url) > 0 {
 		if err := callback(url); err != nil {
-			log.Error("[tso] failed to call back when tso leader url update", zap.String("url", url), errs.ZapError(err))
+			log.Error("[pd] failed to run a callback with the current leader url",
+				zap.String("url", url), errs.ZapError(err))
 		}
 	}
-	c.tsoLeaderUpdatedCb = callback
+	c.AddLeaderSwitchedCallback(callback)
+}
+
+// AddLeaderSwitchedCallback adds callbacks which will be called when the leader
+// in a quorum-based cluster or the primary in a primary/secondary configured cluster
+// is switched.
+func (c *serviceDiscovery) AddLeaderSwitchedCallback(callback leaderSwitchedCallbackFunc) {
+	c.callbacks.addLeaderSwitchedCallback(callback)
+}
+
+// AddMembersChangedCallback adds callbacks which will be called when any primary/secondary
+// in a primary/secondary configured cluster is changed.
+func (c *serviceDiscovery) AddMembersChangedCallback(callback func()) {
+	c.callbacks.addMembersChangedCallback(callback)
 }
 
 // getLeaderURL returns the leader URL.
@@ -867,19 +854,15 @@
 			// If the method is not supported, we set it to pd mode.
 			// TODO: it's a hack way to solve the compatibility issue.
 			// we need to remove this after all maintained version supports the method.
-			if c.serviceModeUpdateCb != nil {
-				c.serviceModeUpdateCb(pdpb.ServiceMode_PD_SVC_MODE)
-			}
+			c.callbacks.onServiceModeUpdate(pdpb.ServiceMode_PD_SVC_MODE)
 			return nil
 		}
 		return err
 	}
 	if clusterInfo == nil || len(clusterInfo.ServiceModes) == 0 {
 		return errors.WithStack(errs.ErrNoServiceModeReturned)
 	}
-	if c.serviceModeUpdateCb != nil {
-		c.serviceModeUpdateCb(clusterInfo.ServiceModes[0])
-	}
+	c.callbacks.onServiceModeUpdate(clusterInfo.ServiceModes[0])
 	return nil
 }
 
@@ -968,9 +951,7 @@
 	}
 	c.urls.Store(urls)
 	// Run callbacks to reflect the membership changes in the leader and followers.
-	for _, cb := range c.membersChangedCbs {
-		cb()
-	}
+	c.callbacks.onMembersChanged()
 	log.Info("[pd] update member urls", zap.Strings("old-urls", oldURLs), zap.Strings("new-urls", urls))
 }
 
@@ -987,13 +968,8 @@
 		c.leader.Store(leaderClient)
 	}
 	// Run callbacks
-	if c.tsoLeaderUpdatedCb != nil {
-		if err := c.tsoLeaderUpdatedCb(url); err != nil {
-			return true, err
-		}
-	}
-	for _, cb := range c.leaderSwitchedCbs {
-		cb()
+	if err := c.callbacks.onLeaderSwitched(url); err != nil {
+		return true, err
 	}
 	log.Info("[pd] switch leader", zap.String("new-leader", url), zap.String("old-leader", oldLeader.GetURL()))
 	return true, err

client/servicediscovery/service_discovery_test.go

@@ -400,7 +400,7 @@ func TestUpdateURLs(t *testing.T) {
 		}
 		return
 	}
-	cli := &serviceDiscovery{option: opt.NewOption()}
+	cli := &serviceDiscovery{callbacks: newServiceCallbacks(), option: opt.NewOption()}
 	cli.urls.Store([]string{})
 	cli.updateURLs(members[1:])
 	re.Equal(getURLs([]*pdpb.Member{members[1], members[3], members[2]}), cli.GetServiceURLs())
@@ -422,6 +422,7 @@ func TestGRPCDialOption(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.TODO(), 500*time.Millisecond)
 	defer cancel()
 	cli := &serviceDiscovery{
+		callbacks:         newServiceCallbacks(),
 		checkMembershipCh: make(chan struct{}, 1),
 		ctx:               ctx,
 		cancel:            cancel,