pillar/watcher: Make goroutinesMonitor stoppable.

Enable the `goroutinesMonitor` to be stopped via a cancellable context
within `GoroutineLeakDetectionParams`, allowing controlled termination
of the monitoring goroutine. This change introduces a `MakeStoppable`
method to set up a cancellable context and a `Stop` method to trigger
the cancellation, allowing tests to end monitoring cleanly.

Additionally, `checkStopCondition` was added to periodically check if
the goroutine should stop.

Updated tests to utilize this functionality, adding verification for
proper start and stop messages in the log output, ensuring that the
monitor operates correctly in both stoppable and unstoppable modes.

Signed-off-by: Nikolay Martyanov <nikolay@zededa.com>

pkg/pillar/cmd/watcher/watcher.go

@@ -4,6 +4,7 @@
 package watcher
 
 import (
+	"context"
 	"flag"
 	"math"
 	"os"
@@ -36,6 +37,9 @@ type GoroutineLeakDetectionParams struct {
 	checkStatsFor  time.Duration
 	keepStatsFor   time.Duration
 	cooldownPeriod time.Duration
+	// Context to make the monitoring goroutine cancellable
+	context context.Context
+	stop    context.CancelFunc
 }
 
 func validateGoroutineLeakDetectionParams(threshold int, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod time.Duration) bool {
@@ -79,6 +83,34 @@ func (gldp *GoroutineLeakDetectionParams) Set(threshold int, checkInterval, chec
 	gldp.mutex.Unlock()
 }
 
+// MakeStoppable creates a cancellable context and a stop function
+func (gldp *GoroutineLeakDetectionParams) MakeStoppable() {
+	gldp.context, gldp.stop = context.WithCancel(context.Background())
+}
+
+func (gldp *GoroutineLeakDetectionParams) isStoppable() bool {
+	return gldp.context != nil
+}
+
+func (gldp *GoroutineLeakDetectionParams) checkStopCondition() bool {
+	if gldp.context != nil {
+		select {
+		case <-gldp.context.Done():
+			return true
+		default:
+			return false
+		}
+	}
+	return false
+}
+
+// Stop cancels the context to stop the monitoring goroutine
+func (gldp *GoroutineLeakDetectionParams) Stop() {
+	if gldp.stop != nil {
+		gldp.stop()
+	}
+}
+
 // Get atomically gets the global goroutine leak detection parameters
 func (gldp *GoroutineLeakDetectionParams) Get() (int, time.Duration, time.Duration, time.Duration, time.Duration) {
 	var threshold int
@@ -337,12 +369,18 @@ func handlePotentialGoroutineLeak() {
 
 // goroutinesMonitor monitors the number of goroutines and detects potential goroutine leaks.
 func goroutinesMonitor(ctx *watcherContext) {
+	log.Functionf("Starting goroutines monitor (stoppable: %v)", ctx.GRLDParams.isStoppable())
 	// Get the initial goroutine leak detection parameters to create the stats slice
 	goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod := ctx.GRLDParams.Get()
 	entriesToKeep := int(keepStatsFor / checkInterval)
 	stats := make([]int, 0, entriesToKeep+1)
 	var lastLeakHandled time.Time
 	for {
+		// Check if we have to stop
+		if ctx.GRLDParams.checkStopCondition() {
+			log.Functionf("Stopping goroutines monitor")
+			return
+		}
 		// Check if we have to resize the stats slice
 		goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod = ctx.GRLDParams.Get()
 		newEntriesToKeep := int(keepStatsFor / checkInterval)

pkg/pillar/cmd/watcher/watcher_test.go

@@ -248,8 +248,10 @@ func TestGoroutinesMonitorNoLeak(t *testing.T) {
 	// Create context with default parameters
 	ctx := &watcherContext{}
 	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+	ctx.GRLDParams.MakeStoppable()
 
 	go goroutinesMonitor(ctx)
+	defer ctx.GRLDParams.Stop()
 
 	timeStart := time.Now()
 	for {
@@ -294,8 +296,10 @@ func TestGoroutinesMonitorLeak(t *testing.T) {
 	// Create context with default parameters
 	ctx := &watcherContext{}
 	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+	ctx.GRLDParams.MakeStoppable()
 
 	go goroutinesMonitor(ctx)
+	defer ctx.GRLDParams.Stop()
 
 	timeStart := time.Now()
 	for {
@@ -345,8 +349,10 @@ func TestGoroutinesMonitorUpdateParamsKeepStatsDecrease(t *testing.T) {
 
 	// Set the parameters
 	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+	ctx.GRLDParams.MakeStoppable()
 
 	go goroutinesMonitor(ctx)
+	defer ctx.GRLDParams.Stop()
 
 	// Wait until we fill the stats slice
 	time.Sleep(2 * keepStatsFor)
@@ -407,8 +413,10 @@ func TestGoroutinesMonitorUpdateParamsKeepStatsIncrease(t *testing.T) {
 
 	// Set the parameters
 	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+	ctx.GRLDParams.MakeStoppable()
 
 	go goroutinesMonitor(ctx)
+	defer ctx.GRLDParams.Stop()
 
 	// Wait until we fill the stats slice
 	time.Sleep(2 * keepStatsFor)
@@ -441,3 +449,92 @@ func TestGoroutinesMonitorUpdateParamsKeepStatsIncrease(t *testing.T) {
 		}
 	}
 }
+
+func TestGoroutineMonitorStops(t *testing.T) {
+	keepStatsFor := 24 * 60 * time.Millisecond
+	goroutinesThreshold := 100
+	checkInterval := 1 * time.Millisecond
+	checkStatsFor := 10 * time.Millisecond
+	cooldownPeriod := 5 * time.Millisecond
+
+	backupOut := logger.Out
+	backupLevel := logger.Level
+	// Create a pipe to capture log output
+	r, w, _ := os.Pipe()
+	logger.Out = w
+	logger.Level = logrus.TraceLevel
+	defer func() {
+		logger.Out = backupOut
+		logger.Level = backupLevel
+	}()
+
+	// Create context with default parameters
+	ctx := &watcherContext{}
+	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+	ctx.GRLDParams.MakeStoppable()
+
+	go goroutinesMonitor(ctx)
+
+	time.Sleep(keepStatsFor / 2)
+
+	ctx.GRLDParams.Stop()
+
+	// Close the pipe
+	_ = w.Close()
+
+	logger.Out = backupOut
+
+	// Read the log output
+	output, _ := io.ReadAll(r)
+
+	msgStart := "Starting goroutines monitor (stoppable: true)"
+	msgStop := "Stopping goroutines monitor"
+	expectedMsgs := []string{msgStart, msgStop}
+	for _, expectedMsg := range expectedMsgs {
+		if !strings.Contains(string(output), expectedMsg) {
+			t.Errorf("Expected log output to contain '%s'", expectedMsg)
+		}
+	}
+}
+
+func TestGoroutineMonitorRunsFineUnstoppable(t *testing.T) {
+	keepStatsFor := 24 * 60 * time.Millisecond
+	goroutinesThreshold := 100
+	checkInterval := 1 * time.Millisecond
+	checkStatsFor := 10 * time.Millisecond
+	cooldownPeriod := 5 * time.Millisecond
+
+	backupOut := logger.Out
+	backupLevel := logger.Level
+	// Create a pipe to capture log output
+	r, w, _ := os.Pipe()
+	logger.Out = w
+	logger.Level = logrus.TraceLevel
+	defer func() {
+		logger.Out = backupOut
+		logger.Level = backupLevel
+	}()
+
+	// Create context with default parameters
+	ctx := &watcherContext{}
+	ctx.GRLDParams.Set(goroutinesThreshold, checkInterval, checkStatsFor, keepStatsFor, cooldownPeriod)
+
+	go goroutinesMonitor(ctx)
+
+	time.Sleep(keepStatsFor / 2)
+
+	// Close the pipe
+	_ = w.Close()
+
+	// Read the log output
+	output, _ := io.ReadAll(r)
+
+	msgStart := "Starting goroutines monitor (stoppable: false)"
+	expectedMsgs := []string{msgStart}
+	for _, expectedMsg := range expectedMsgs {
+		if !strings.Contains(string(output), expectedMsg) {
+			t.Errorf("Expected log output to contain '%s'", expectedMsg)
+		}
+	}
+
+}