fire and forget goroutine for discover fallback clients

Author: linglingye001

azureappconfiguration/client_manager.go

@@ -13,6 +13,7 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
@@ -25,14 +26,17 @@ type configurationClientManager struct {
 	replicaDiscoveryEnabled   bool
 	clientOptions             *azappconfig.ClientOptions
 	staticClient              *configurationClientWrapper
-	dynamicClients            []*configurationClientWrapper
+	dynamicClients            atomic.Pointer[[]*configurationClientWrapper] // atomic pointer to slice
 	endpoint                  string
 	validDomain               string
 	credential                azcore.TokenCredential
 	secret                    string
 	id                        string
 	lastFallbackClientAttempt time.Time
 	lastFallbackClientRefresh time.Time
+
+	// discoveryInProgress prevents concurrent replica discovery operations
+	discoveryInProgress atomic.Bool
 }
 
 // configurationClientWrapper wraps an Azure App Configuration client with additional metadata
@@ -110,7 +114,12 @@ func (manager *configurationClientManager) initializeClient(authOptions Authenti
 
 func (manager *configurationClientManager) getClients(ctx context.Context) ([]*configurationClientWrapper, error) {
 	currentTime := time.Now()
-	clients := make([]*configurationClientWrapper, 0, 1+len(manager.dynamicClients))
+	dynamicClients := manager.dynamicClients.Load() // atomic read
+	clientsCapacity := 1
+	if dynamicClients != nil {
+		clientsCapacity += len(*dynamicClients)
+	}
+	clients := make([]*configurationClientWrapper, 0, clientsCapacity)
 
 	// Add the static client if it is not in backoff
 	if currentTime.After(manager.staticClient.backOffEndTime) {
@@ -122,16 +131,18 @@ func (manager *configurationClientManager) getClients(ctx context.Context) ([]*c
 	}
 
 	if currentTime.After(manager.lastFallbackClientAttempt.Add(minimalClientRefreshInterval)) &&
-		(manager.dynamicClients == nil ||
+		(dynamicClients == nil ||
 			currentTime.After(manager.lastFallbackClientRefresh.Add(fallbackClientRefreshExpireInterval))) {
 		manager.lastFallbackClientAttempt = currentTime
 		url, _ := url.Parse(manager.endpoint)
-		manager.discoverFallbackClients(ctx, url.Host)
+		manager.discoverFallbackClients(url.Host)
 	}
 
-	for _, clientWrapper := range manager.dynamicClients {
-		if currentTime.After(clientWrapper.backOffEndTime) {
-			clients = append(clients, clientWrapper)
+	if dynamicClients != nil {
+		for _, clientWrapper := range *dynamicClients {
+			if currentTime.After(clientWrapper.backOffEndTime) {
+				clients = append(clients, clientWrapper)
+			}
 		}
 	}
 
@@ -144,21 +155,36 @@ func (manager *configurationClientManager) refreshClients(ctx context.Context) {
 		currentTime.After(manager.lastFallbackClientAttempt.Add(minimalClientRefreshInterval)) {
 		manager.lastFallbackClientAttempt = currentTime
 		url, _ := url.Parse(manager.endpoint)
-		manager.discoverFallbackClients(ctx, url.Host)
+		manager.discoverFallbackClients(url.Host)
 	}
 }
 
-func (manager *configurationClientManager) discoverFallbackClients(ctx context.Context, host string) {
-	newCtx, cancel := context.WithTimeout(ctx, failoverTimeout)
-	defer cancel()
-
-	srvTargetHosts, err := querySrvTargetHost(newCtx, host)
-	if err != nil {
-		log.Printf("failed to discover fallback clients for %s: %v", host, err)
-		return
+func (manager *configurationClientManager) discoverFallbackClients(host string) {
+	if !manager.discoveryInProgress.CompareAndSwap(false, true) {
+		return // Another discovery is already in progress
 	}
 
-	manager.processSrvTargetHosts(srvTargetHosts)
+	// Reset the flag when we're done
+	defer manager.discoveryInProgress.Store(false)
+
+	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				log.Printf("panic in replica discovery: %v", r)
+			}
+		}()
+
+		discoveryCtx, cancel := context.WithTimeout(context.Background(), failoverTimeout)
+		defer cancel()
+
+		srvTargetHosts, err := querySrvTargetHost(discoveryCtx, host)
+		if err != nil {
+			log.Printf("failed to discover fallback clients for %s: %v", host, err)
+			return
+		}
+
+		manager.processSrvTargetHosts(srvTargetHosts)
+	}()
 }
 
 func (manager *configurationClientManager) processSrvTargetHosts(srvTargetHosts []string) {
@@ -188,7 +214,7 @@ func (manager *configurationClientManager) processSrvTargetHosts(srvTargetHosts
 		}
 	}
 
-	manager.dynamicClients = newDynamicClients
+	manager.dynamicClients.Store(&newDynamicClients) // atomic write
 	manager.lastFallbackClientRefresh = time.Now()
 }