Change EnableTSOFollowerProxy may not take effect

[rleungx]

Bug Report

pd/client/tso_dispatcher.go

Lines 333 to 402 in c1ee9cf

	func (c *tsoClient) handleDispatcher(
	dispatcherCtx context.Context,
	dc string,
	tbc *tsoBatchController,
	) {
	var (
	err error
	streamURL string
	stream tsoStream
	streamCtx context.Context
	cancel context.CancelFunc
	// url -> connectionContext
	connectionCtxs sync.Map
	)
	defer func() {
	log.Info("[tso] exit tso dispatcher", zap.String("dc-location", dc))
	// Cancel all connections.
	connectionCtxs.Range(func(_, cc any) bool {
	cc.(*tsoConnectionContext).cancel()
	return true
	})
	// Clear the tso batch controller.
	tbc.clear()
	c.wg.Done()
	}()
	// Call updateTSOConnectionCtxs once to init the connectionCtxs first.
	c.updateTSOConnectionCtxs(dispatcherCtx, dc, &connectionCtxs)
	// Only the Global TSO needs to watch the updateTSOConnectionCtxsCh to sense the
	// change of the cluster when TSO Follower Proxy is enabled.
	// TODO: support TSO Follower Proxy for the Local TSO.
	if dc == globalDCLocation {
	go func() {
	var updateTicker = &time.Ticker{}
	setNewUpdateTicker := func(ticker *time.Ticker) {
	if updateTicker.C != nil {
	updateTicker.Stop()
	}
	updateTicker = ticker
	}
	// Set to nil before returning to ensure that the existing ticker can be GC.
	defer setNewUpdateTicker(nil)
	for {
	select {
	case <-dispatcherCtx.Done():
	return
	case <-c.option.enableTSOFollowerProxyCh:
	enableTSOFollowerProxy := c.option.getEnableTSOFollowerProxy()
	log.Info("[tso] tso follower proxy status changed",
	zap.String("dc-location", dc),
	zap.Bool("enable", enableTSOFollowerProxy))
	if enableTSOFollowerProxy && updateTicker.C == nil {
	// Because the TSO Follower Proxy is enabled,
	// the periodic check needs to be performed.
	setNewUpdateTicker(time.NewTicker(memberUpdateInterval))
	} else if !enableTSOFollowerProxy && updateTicker.C != nil {
	// Because the TSO Follower Proxy is disabled,
	// the periodic check needs to be turned off.
	setNewUpdateTicker(&time.Ticker{})
	} else {
	// The status of TSO Follower Proxy does not change, and updateTSOConnectionCtxs is not triggered
	continue
	}
	case <-updateTicker.C:
	case <-c.updateTSOConnectionCtxsCh:
	}
	c.updateTSOConnectionCtxs(dispatcherCtx, dc, &connectionCtxs)
	}
	}()
	}

If the option is true at line 359, it might connect to the follower. After that, the option is changed to false at line 380. This change may not take effect since the enableTSOFollowerProxy is false and updateTicker.C is nil.

It's better to initialize the ticker before stepping into the loop.