fix issue with closing flush signal channel (#7384)

agent/agent.go

@@ -556,6 +556,7 @@ func (a *Agent) flushLoop(
 	// watch for flush requests
 	flushRequested := make(chan os.Signal, 1)
 	watchForFlushSignal(flushRequested)
+	defer stopListeningForFlushSignal(flushRequested)
 
 	// align to round interval
 	if a.Config.Agent.RoundInterval {

agent/agent_posix.go

@@ -12,5 +12,8 @@ const flushSignal = syscall.SIGUSR1
 
 func watchForFlushSignal(flushRequested chan os.Signal) {
 	signal.Notify(flushRequested, flushSignal)
+}
+
+func stopListeningForFlushSignal(flushRequested chan os.Signal) {
 	defer signal.Stop(flushRequested)
 }

agent/agent_windows.go

@@ -5,5 +5,9 @@ package agent
 import "os"
 
 func watchForFlushSignal(flushRequested chan os.Signal) {
-	// not implemented
+	// not supported
+}
+
+func stopListeningForFlushSignal(flushRequested chan os.Signal) {
+	// not supported
 }