fix threading (!?) plz test

README.md

@@ -6,11 +6,10 @@
 
 **Because people are asking... Linspector is actually more some kind of a research project for evaluating stuff, but a lot of the code is used in some private projects. I am working on the API definition mostly and there is a lot of code that must be refactored/rewrited ASAP. (2023.11.29)**
 
-**Linspector is currently not process safe because of the GIL! I am refactoring a lot of stuff
-at the moment. When running the scheduler in thread-mode everything is fine, but I really want to make it possible to run Linspector using the process-mode of APScheduler...**
-
-**THE CORE NEEDS A REDESIGN AND PARTLY REWRITE TO BE FULLY PROCESS SAFE! I AM WORKING ON THIS
-NOW. THE CONFIGURATION INTERFACE WILL NOT BE CHANGED! (2023.10.22)**
+**Linspector is now thread-safe in scheduler thread-mode. Shared mutable state (Environment,
+Monitor error counts) is protected by locks and the scheduler starts after daemonization to
+avoid fork-with-threads issues. Process-mode (multi-process) is still not supported — that
+requires a larger architectural redesign with serializable state and IPC.**
 
 ## About
 

bin/linspector

@@ -194,6 +194,7 @@ def linspector():
             log.critical('daemon error: {0}'.format(err))
             sys.exit(1)
     else:
+        linspector.start()
         try:
             signal.pause()
         except KeyboardInterrupt:

linspector/environment.py

@@ -4,6 +4,9 @@ Copyright (c) 2013-2023 Johannes Findeisen <you@hanez.org>. All Rights Reserved.
 See LICENSE.
 """
 
+import threading
+
+
 class Environment:
     """
     Object for storing environment variables at runtime. These variables must not affect the
@@ -12,9 +15,11 @@ class Environment:
 
     def __init__(self, log):
         self._env = {}
+        self._lock = threading.Lock()
         self._log = log
 
     def get_env_var(self, key):
+        with self._lock:
             if key in self._env:
                 return self._env[key]
             else:
@@ -31,7 +36,8 @@ class Environment:
                 return None
 
     def set_env_var(self, key, value):
-        if self._env[key]:
+        with self._lock:
+            if self._env.get(key):
                 self._log('warning', __name__, 'environment var "' + key +
                           ' existed and was overwritten!')
 

linspector/linspector.py

@@ -35,6 +35,7 @@ class Linspector:
         self._plugin_list = []
         self._plugins = plugins
         self._scheduler = scheduler
+        self._started = False
 
         # load plugins
         if configuration.get_option('linspector', 'plugins'):
@@ -145,5 +146,8 @@ class Linspector:
 
         print('Number of scheduled monitors: ' + str(monitor_count))
 
-        if configuration.get_option('linspector', 'start_scheduler') == 'true':
+    def start(self):
+        if not self._started and \
+                self._configuration.get_option('linspector', 'start_scheduler') == 'true':
             self._scheduler['linspector'].start()
+            self._started = True

linspector/linspectord.py

@@ -88,6 +88,8 @@ class Linspectord:
 
         # start the daemon.
         self.daemonize()
+        # start scheduler after fork to avoid threading issues
+        self._linspector.start()
         self.run()
 
     def stop(self):

linspector/monitor.py

@@ -6,6 +6,7 @@ See LICENSE.
 
 import configparser
 import importlib
+import threading
 import time
 
 
@@ -17,6 +18,7 @@ class Monitor:
         self._enabled = True
         self._environment = environment
         self._error_count = 0
+        self._lock = threading.Lock()
         self._host = monitor_configuration.get('monitor', 'host')
 
         try:
@@ -123,12 +125,15 @@ class Monitor:
                                                                      self._service, **self._args)
 
                 notification_error_mode = 'decrease'
+                with self._lock:
                     if self._result['status'] == 'ERROR':
                         self._error_count += 1
                     elif self._result['status'] == 'OK':
-                    if self._configuration.get_option('linspector', 'notification_error_mode'):
+                        if self._configuration.get_option('linspector',
+                                                          'notification_error_mode'):
                             configuration_notification_error_mode = (
-                            self._configuration.get_option('linspector', 'notification_error_mode'))
+                                self._configuration.get_option('linspector',
+                                                               'notification_error_mode'))
                             if (configuration_notification_error_mode == 'decrease' or
                                     configuration_notification_error_mode == 'reset'):
                                 notification_error_mode = (