replace atomic with sync.Once

changelogs/head.asciidoc

@@ -13,7 +13,7 @@ https://github.com/elastic/apm-server/compare/8.15\...main[View commits]
 
 [float]
 ==== Deprecations
-- Support for Jaeger will be deprecated in a future release {pull}13809[13809]
+- Support for Jaeger is now deprecated, and will be removed in a future release {pull}13809[13809]
 
 [float]
 ==== Intake API Changes

internal/beater/jaeger/grpc.go

@@ -22,7 +22,7 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
-	"sync/atomic"
+	"sync"
 
 	jaegermodel "github.com/jaegertracing/jaeger/model"
 	"github.com/jaegertracing/jaeger/proto-gen/api_v2"
@@ -79,19 +79,16 @@ func RegisterGRPCServices(
 
 	logger.Info(deprecationNotice)
 
-	var warningCollector atomic.Int32
-	api_v2.RegisterCollectorServiceServer(srv, &grpcCollector{&warningCollector, logger, traceConsumer})
-
-	var warningSampling atomic.Int32
-	api_v2.RegisterSamplingManagerServer(srv, &grpcSampler{&warningSampling, logger, fetcher})
+	api_v2.RegisterCollectorServiceServer(srv, &grpcCollector{sync.Once{}, logger, traceConsumer})
+	api_v2.RegisterSamplingManagerServer(srv, &grpcSampler{sync.Once{}, logger, fetcher})
 }
 
 // grpcCollector implements Jaeger api_v2 protocol for receiving tracing data
 type grpcCollector struct {
 	// Use an atomic counter to ensure concurrent safety.
-	warningPrinted *atomic.Int32
-	logger         *zap.Logger
-	consumer       consumer.Traces
+	once     sync.Once
+	logger   *zap.Logger
+	consumer consumer.Traces
 }
 
 // AuthenticateUnaryCall authenticates CollectorService calls.
@@ -132,9 +129,11 @@ func (c *grpcCollector) RequestMetrics(fullMethodName string) map[request.Result
 // The implementation of the protobuf contract is based on the open-telemetry implementation at
 // https://github.com/open-telemetry/opentelemetry-collector/tree/master/receiver/jaegerreceiver
 func (c *grpcCollector) PostSpans(ctx context.Context, r *api_v2.PostSpansRequest) (*api_v2.PostSpansResponse, error) {
-	if c.warningPrinted.CompareAndSwap(0, 1) {
+
+	c.once.Do(func() {
 		c.logger.Warn(deprecationNotice)
-	}
+	})
+
 	if err := c.postSpans(ctx, r.Batch); err != nil {
 		return nil, err
 	}
@@ -162,9 +161,9 @@ var (
 
 type grpcSampler struct {
 	// Use an atomic counter to ensure concurrent safety.
-	warningPrinted *atomic.Int32
-	logger         *zap.Logger
-	fetcher        agentcfg.Fetcher
+	once    sync.Once
+	logger  *zap.Logger
+	fetcher agentcfg.Fetcher
 }
 
 // GetSamplingStrategy implements the api_v2/sampling.proto.
@@ -174,9 +173,9 @@ func (s *grpcSampler) GetSamplingStrategy(
 	ctx context.Context,
 	params *api_v2.SamplingStrategyParameters) (*api_v2.SamplingStrategyResponse, error) {
 
-	if s.warningPrinted.CompareAndSwap(0, 1) {
+	s.once.Do(func() {
 		s.logger.Warn(deprecationNotice)
-	}
+	})
 
 	samplingRate, err := s.fetchSamplingRate(ctx, params.ServiceName)
 	if err != nil {