From ff65bbde146f792897f0274094097733e67020dc Mon Sep 17 00:00:00 2001
From: Klaus-Uwe Mitterer <git@kumi.email>
Date: Sat, 2 May 2020 12:16:17 +0000
Subject: [PATCH] Implement native lock in hallmonitor

---
 server/hallmonitor.py | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/server/hallmonitor.py b/server/hallmonitor.py
index 2c134f1..1f1f5a3 100644
--- a/server/hallmonitor.py
+++ b/server/hallmonitor.py
@@ -7,6 +7,11 @@ import configparser
 import handler
 import time
 import glob
+import ftncl
+import signal
+import errno
+
+from contextlib import contextmanager
 
 processes = {}
 
@@ -57,5 +62,33 @@ def run():
         finally:
             time.sleep(30)
 
+@contextmanager
+def timeout(seconds):
+    def timeout_handler(signum, frame):
+        pass
+
+    original_handler = signal.signal(signal.SIGALRM, timeout_handler)
+
+    try:
+        signal.alarm(seconds)
+        yield
+
+    finally:
+        signal.alarm(0)
+        signal.signal(signal.SIGALRM, original_handler)
+
+def create_lock():
+    with timeout(1):
+        fileobj = open('/tmp/panosteal/monitor.lock', 'w+')
+        try:
+            fcntl.flock(fileobj.fileno(), fcntl.LOCK_EX)
+        except IOError as e:
+            if e.errno != errno.EINTR:
+                raise e
+            exit("Already running - exiting")
+        return fileobj
+    exit("An error has occurred - exiting")
+
 if __name__ == "__main__":
+    create_lock()
     run()