From 1f8ec65e97a9d607b8f975d51d4ceae268aad504 Mon Sep 17 00:00:00 2001
From: Bruno Kleinert <fuddl@debian.org>
Date: Fri, 9 Jan 2026 09:00:21 +0100
Subject: [PATCH] Check if stdin is a tty

When stdin links to /dev/null, which is the case for systemd service
units, select() returns immediately. That causes the loop to endlessly
read() 0 bytes and eats up 100% of a processor core.

isatty() checks if railcontrol has a "real" stdin available. If that is not the
case, do not select() and read() stdin but use the 1s delay as for
silent mode.
---
 RailControl.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/RailControl.cpp b/RailControl.cpp
index e130014d..6cb925a2 100644
--- a/RailControl.cpp
+++ b/RailControl.cpp
@@ -24,7 +24,7 @@ along with RailControl; see the file LICENCE. If not see
 #include <iostream>
 #include <signal.h>
 #include <sstream>
-#include <unistd.h>		//close;
+#include <unistd.h>		//close; isatty
 #include <vector>
 
 #include "ArgumentHandler.h"
@@ -183,7 +183,7 @@ int main (int argc, char* argv[])
 		// wait for q or r followed by \n or SIGINT or SIGTERM
 		do
 		{
-			if (silent)
+			if (!isatty(STDIN_FILENO) || silent)
 			{
 				Utils::Utils::SleepForSeconds(1);
 			}