In the start TCP, UDP and Seriel server, we are running a quick check (#242)

to see weather the thread in which the helpers are executed are the
Main thread or the spawned thread.

This infomation is passed to reactor.run() to the flag
installSignalHandlers. True is passed if the thread is a main
thread, else false.

This is done to prevent errors when running the helpers from a
spawned thread.

Author: rahulraghu94

pymodbus/server/async.py

@@ -6,6 +6,7 @@
 from binascii import b2a_hex
 from twisted.internet import protocol
 from twisted.internet.protocol import ServerFactory
+from twisted.internet import reactor
 
 from pymodbus.constants import Defaults
 from pymodbus.factory import ServerDecoder
@@ -18,7 +19,7 @@
 from pymodbus.pdu import ModbusExceptions as merror
 from pymodbus.internal.ptwisted import InstallManagementConsole
 from pymodbus.compat import byte2int
-from twisted.internet import reactor
+from pymodbus.compat import IS_PYTHON3
 
 #---------------------------------------------------------------------------#
 # Logging
@@ -204,6 +205,21 @@ def _send(self, message, addr):
 #---------------------------------------------------------------------------#
 # Starting Factories
 #---------------------------------------------------------------------------#
+def _is_main_thread():
+    import threading
+
+    if IS_PYTHON3:
+        if threading.current_thread() != threading.main_thread():
+            _logger.debug("Starting in spawned thread")
+            return False
+    else:
+        if not isinstance(threading.current_thread(), threading._MainThread):
+            _logger.debug("Starting in spawned thread")
+            return False
+    _logger.debug("Starting in Main thread")
+    return True
+
+
 def StartTcpServer(context, identity=None, address=None, console=False, **kwargs):
     ''' Helper method to start the Modbus Async TCP server
 
@@ -223,7 +239,7 @@ def StartTcpServer(context, identity=None, address=None, console=False, **kwargs
 
     _logger.info("Starting Modbus TCP Server on %s:%s" % address)
     reactor.listenTCP(address[1], factory, interface=address[0])
-    reactor.run()
+    reactor.run(installSignalHandlers=_is_main_thread())
 
 
 def StartUdpServer(context, identity=None, address=None, **kwargs):
@@ -242,7 +258,7 @@ def StartUdpServer(context, identity=None, address=None, **kwargs):
 
     _logger.info("Starting Modbus UDP Server on %s:%s" % address)
     reactor.listenUDP(address[1], server, interface=address[0])
-    reactor.run()
+    reactor.run(installSignalHandlers=_is_main_thread())
 
 
 def StartSerialServer(context, identity=None,
@@ -272,7 +288,7 @@ def StartSerialServer(context, identity=None,
     protocol = factory.buildProtocol(None)
     SerialPort.getHost = lambda self: port # hack for logging
     SerialPort(protocol, port, reactor, baudrate)
-    reactor.run()
+    reactor.run(installSignalHandlers=_is_main_thread())
 
 #---------------------------------------------------------------------------#
 # Exported symbols