From 37f8aa3c7e7a48751ef219af148005ccec4963be Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Tich=C3=A1k?= <michal.tichak@cern.ch>
Date: Thu, 21 Aug 2025 13:05:01 +0200
Subject: [PATCH 1/2] [monitoring] fixed racecondition on Run monitoring and
 Stop

---
 common/monitoring/monitoring.go | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/common/monitoring/monitoring.go b/common/monitoring/monitoring.go
index ca21056b..26e336ad 100644
--- a/common/monitoring/monitoring.go
+++ b/common/monitoring/monitoring.go
@@ -30,6 +30,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"sync/atomic"
 	"time"
 
 	"github.com/AliceO2Group/Control/common/logger"
@@ -38,8 +39,8 @@ import (
 )
 
 var (
-	// scraping endpoint implementation
-	server *http.Server
+	// atomic holder for the HTTP server instance
+	server atomic.Pointer[http.Server]
 	// objects to store incoming metrics
 	metricsInternal          *MetricsAggregate
 	metricsHistogramInternal *MetricsReservoirSampling
@@ -154,33 +155,30 @@ func handleFunc(endpointName string) {
 //
 // If we attempt send more messages than the size of the buffer, these overflowing messages will be ignored and warning will be logged.
 func Run(port uint16, endpointName string) error {
-	if IsRunning() {
+	srv := &http.Server{Addr: fmt.Sprintf(":%d", port)}
+	// only one Run should initialize and serve
+	if !server.CompareAndSwap(nil, srv) {
 		return nil
 	}
-
 	initChannels()
-
 	go eventLoop()
-
-	server = &http.Server{Addr: fmt.Sprintf(":%d", port)}
 	handleFunc(endpointName)
-	return server.ListenAndServe()
+	// block until Shutdown is called
+	return srv.ListenAndServe()
 }
 
 func Stop() {
-	if !IsRunning() {
+	srv := server.Swap(nil)
+	if srv == nil {
 		return
 	}
-
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
-	server.Shutdown(ctx)
-
+	srv.Shutdown(ctx)
 	endChannel <- struct{}{}
 	<-endChannel
-	server = nil
 }
 
 func IsRunning() bool {
-	return server != nil
+	return server.Load() != nil
 }

From 3494a46d566aa1c34855edb07e88fcd6d49c3dc0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Tich=C3=A1k?= <michal.tichak@cern.ch>
Date: Tue, 26 Aug 2025 15:44:24 +0200
Subject: [PATCH 2/2] fixup! [monitoring] fixed racecondition on Run monitoring
 and Stop

---
 common/monitoring/monitoring.go      | 12 ++++++------
 common/monitoring/monitoring_test.go | 12 ++----------
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/common/monitoring/monitoring.go b/common/monitoring/monitoring.go
index 26e336ad..91dbd417 100644
--- a/common/monitoring/monitoring.go
+++ b/common/monitoring/monitoring.go
@@ -155,26 +155,26 @@ func handleFunc(endpointName string) {
 //
 // If we attempt send more messages than the size of the buffer, these overflowing messages will be ignored and warning will be logged.
 func Run(port uint16, endpointName string) error {
-	srv := &http.Server{Addr: fmt.Sprintf(":%d", port)}
+	localServer := &http.Server{Addr: fmt.Sprintf(":%d", port)}
 	// only one Run should initialize and serve
-	if !server.CompareAndSwap(nil, srv) {
+	if !server.CompareAndSwap(nil, localServer) {
 		return nil
 	}
 	initChannels()
 	go eventLoop()
 	handleFunc(endpointName)
 	// block until Shutdown is called
-	return srv.ListenAndServe()
+	return localServer.ListenAndServe()
 }
 
 func Stop() {
-	srv := server.Swap(nil)
-	if srv == nil {
+	localServer := server.Swap(nil)
+	if localServer == nil {
 		return
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
-	srv.Shutdown(ctx)
+	localServer.Shutdown(ctx)
 	endChannel <- struct{}{}
 	<-endChannel
 }
diff --git a/common/monitoring/monitoring_test.go b/common/monitoring/monitoring_test.go
index 67540d0f..b0da3843 100644
--- a/common/monitoring/monitoring_test.go
+++ b/common/monitoring/monitoring_test.go
@@ -81,20 +81,12 @@ func TestStartMultipleStop(t *testing.T) {
 	Stop()
 }
 
-func cleaningUpAfterTest() {
-	Stop()
-}
-
-func initTest() {
-	go Run(12345, "notimportant")
-}
-
 // decorator function that properly inits and cleans after higher level test of Monitoring package
 func testFunction(t *testing.T, testToRun func(*testing.T)) {
-	initTest()
+	go Run(12345, "notimportant")
 	isRunningWithTimeout(t, time.Second)
 	testToRun(t)
-	cleaningUpAfterTest()
+	Stop()
 }
 
 func TestSendingSingleMetric(t *testing.T) {