Add lock around argtypes to prevent race condition, Fix Issue 7

<rev> Add lock around `argtypes` to prevent race condition between
setting `argtypes` and calling functions, in cases the functions run in
parallel.

Some special cases needed unconditional locks around both the setting of
`argtypes` and the actual function call, like the variadic power-up
state functions in system.py, and the register events functions in
task.py.

<rev> Fix issue - `tests/max_config/nidaqmxMaxConfig.nce` is a binary
file and hard to track in git history, since I'm modifying the file
anyway.
#7

nidaqmx/_lib.py

@@ -3,12 +3,13 @@
 from __future__ import print_function
 from __future__ import unicode_literals
 
+from ctypes.util import find_library
 import ctypes
+from numpy.ctypeslib import ndpointer
+import platform
 import six
 import sys
-import platform
-from ctypes.util import find_library
-from numpy.ctypeslib import ndpointer
+import threading
 
 from nidaqmx.errors import Error
 
@@ -131,10 +132,16 @@ class DaqFunctionImporter(object):
 
     def __init__(self, library):
         self._library = library
+        self._lib_lock = threading.Lock()
 
     def __getattr__(self, function):
         try:
-            return getattr(self._library, function)
+            cfunc = getattr(self._library, function)
+            if not hasattr(cfunc, 'arglock'):
+                with self._lib_lock:
+                    if not hasattr(cfunc, 'arglock'):
+                        cfunc.arglock = threading.Lock()
+            return cfunc
         except AttributeError:
             raise DaqFunctionNotSupportedError(
                 'The NI-DAQmx function "{0}" is not supported in this '

nidaqmx/_task_modules/ao_channel_collection.py

@@ -81,9 +81,13 @@ def add_ao_current_chan(
             Indicates the newly created channel object.
         """
         cfunc = lib_importer.windll.DAQmxCreateAOCurrentChan
-        cfunc.argtypes = [
-            lib_importer.task_handle, ctypes_byte_str, ctypes_byte_str,
-            ctypes.c_double, ctypes.c_double, ctypes.c_int, ctypes_byte_str]
+        if cfunc.argtypes is None:
+            with cfunc.arglock:
+                if cfunc.argtypes is None:
+                    cfunc.argtypes = [
+                        lib_importer.task_handle, ctypes_byte_str,
+                        ctypes_byte_str, ctypes.c_double, ctypes.c_double,
+                        ctypes.c_int, ctypes_byte_str]
 
         error_code = cfunc(
             self._handle, physical_channel, name_to_assign_to_channel,
@@ -124,9 +128,13 @@ def add_ao_func_gen_chan(
             Indicates the newly created channel object.
         """
         cfunc = lib_importer.windll.DAQmxCreateAOFuncGenChan
-        cfunc.argtypes = [
-            lib_importer.task_handle, ctypes_byte_str, ctypes_byte_str,
-            ctypes.c_int, ctypes.c_double, ctypes.c_double, ctypes.c_double]
+        if cfunc.argtypes is None:
+            with cfunc.arglock:
+                if cfunc.argtypes is None:
+                    cfunc.argtypes = [
+                        lib_importer.task_handle, ctypes_byte_str,
+                        ctypes_byte_str, ctypes.c_int, ctypes.c_double,
+                        ctypes.c_double, ctypes.c_double]
 
         error_code = cfunc(
             self._handle, physical_channel, name_to_assign_to_channel,
@@ -169,9 +177,13 @@ def add_ao_voltage_chan(
             Indicates the newly created channel object.
         """
         cfunc = lib_importer.windll.DAQmxCreateAOVoltageChan
-        cfunc.argtypes = [
-            lib_importer.task_handle, ctypes_byte_str, ctypes_byte_str,
-            ctypes.c_double, ctypes.c_double, ctypes.c_int, ctypes_byte_str]
+        if cfunc.argtypes is None:
+            with cfunc.arglock:
+                if cfunc.argtypes is None:
+                    cfunc.argtypes = [
+                        lib_importer.task_handle, ctypes_byte_str,
+                        ctypes_byte_str, ctypes.c_double, ctypes.c_double,
+                        ctypes.c_int, ctypes_byte_str]
 
         error_code = cfunc(
             self._handle, physical_channel, name_to_assign_to_channel,

nidaqmx/_task_modules/channel_collection.py

@@ -116,8 +116,12 @@ def channel_names(self):
             channel collection.
         """
         cfunc = lib_importer.windll.DAQmxGetTaskChannels
-        cfunc.argtypes = [
-            lib_importer.task_handle, ctypes.c_char_p, ctypes.c_uint]
+        if cfunc.argtypes is None:
+            with cfunc.arglock:
+                if cfunc.argtypes is None:
+                    cfunc.argtypes = [
+                        lib_importer.task_handle, ctypes.c_char_p,
+                        ctypes.c_uint]
 
         temp_size = 0
         while True: