Try to make PrologicUSB thread safe

hpib.py

@@ -3,6 +3,7 @@ import time
 import re
 import platform
 import sys
+from threading import Lock
 
 
 class PortDevice(object):
@@ -27,6 +28,7 @@ class PrologixGpibUsb(PortDevice):
             max_device_num, port, port_format = self._set_default_platform_values()
 
         self._validate_port(port)
+        self._lock = Lock()
 
         if verbose:
             print("Looking for ports such as %s in range %d on %s" % \
@@ -101,7 +103,8 @@ class PrologixGpibUsb(PortDevice):
             command = "++addr " + str(hpib_address) + chr(10) + command
             self._hpib_address = hpib_address
 
-        self._write_serial(command + chr(10))
+        with self._lock:
+            self._write_serial(command + chr(10))
 
     def query(self, hpib_address, query, count=80):
         if hpib_address != self._hpib_address:
@@ -109,8 +112,9 @@ class PrologixGpibUsb(PortDevice):
             self._hpib_address = hpib_address
 
         query += chr(10) + "++read eoi" + chr(10)
-        self._write_serial(query)
-        line = self._serialPort.readline()
+        with self._lock:
+            self._write_serial(query)
+            line = self._serialPort.readline()
         return line[:-1]
 
     def set_local(self, hpib_address):