Make initialization of CamrasHpibDevice thread safe

camrasdevices.py

@@ -54,24 +54,27 @@ from astropy.units import Quantity
 
 import hpib
 import serial.threaded
+import threading
 
 
 class CamrasHpibDevice(object):
     """Wrapper around HPIB commands"""
 
     command_thread = None
+    _initialization_lock = threading.Lock()
 
     def __init__(self, address, check_frequency=True):
         self.hpib_address = address
         self._check_frequency = check_frequency
 
-        if not CamrasHpibDevice.command_thread:
-            serial_port = serial.Serial("/dev/ttyUSB0")
-            CamrasHpibDevice.command_thread = serial.threaded.ReaderThread(serial_port,
-                                                                           hpib.GPIBProtocol)
-            CamrasHpibDevice.command_thread.start()
-            CamrasHpibDevice.command_thread._connection_made.wait()
-            CamrasHpibDevice.command_thread.protocol.init_hpib()
+        with self._initialization_lock:
+            if not CamrasHpibDevice.command_thread:
+                serial_port = serial.Serial("/dev/ttyUSB0")
+                CamrasHpibDevice.command_thread = serial.threaded.ReaderThread(serial_port,
+                                                                               hpib.GPIBProtocol)
+                CamrasHpibDevice.command_thread.start()
+                CamrasHpibDevice.command_thread._connection_made.wait()
+                CamrasHpibDevice.command_thread.protocol.init_hpib()
 
     def command(self, command_string, prepend_address=True):
         """Send a command to the HPIB command thread