Cache device_query results

Since I'll be calling it more for #104

digits/config.py

@@ -418,7 +418,7 @@ def name():
 
     def prompt_message(self):
         s = 'Attached devices:\n'
-        for device_id, gpu in enumerate(self.query_gpus()):
+        for device_id, gpu in enumerate(device_query.get_devices()):
             s += 'Device #%s:\n' % device_id
             s += '\t%-20s %s\n' % ('Name', gpu.name)
             s += '\t%-20s %s.%s\n' % ('Compute capability', gpu.major, gpu.minor)
@@ -431,19 +431,19 @@ def optional(self):
         return True
 
     def suggestions(self):
-        if len(self.query_gpus()) > 0:
+        if len(device_query.get_devices()) > 0:
             return [Suggestion(
-                ','.join([str(x) for x in xrange(len(self.query_gpus()))]),
+                ','.join([str(x) for x in xrange(len(device_query.get_devices()))]),
                 'D', desc='default', default=True)]
         else:
             return []
 
     @classmethod
     def visibility(self):
-        if len(self.query_gpus()) == 0:
+        if len(device_query.get_devices()) == 0:
             # Nothing to see here
             return -1
-        if len(self.query_gpus()) == 1:
+        if len(device_query.get_devices()) == 1:
             # Use just the one GPU by default
             return 0
         else:
@@ -455,7 +455,7 @@ def validate(cls, value):
             return value
 
         choices = []
-        gpus = cls.query_gpus()
+        gpus = device_query.get_devices()
 
         if not gpus:
             return ''
@@ -488,17 +488,6 @@ def convert_size(cls, size):
         else:
             return '0B'
 
-    @classmethod
-    def query_gpus(cls):
-        """
-        Return a list of device_query.CudaDeviceProp objects which contain all
-        the available information on each device
-        Order is preserved in this list - item 0 is gpu #0
-        """
-        if not hasattr(cls, 'device_list'):
-            cls.device_list = device_query.get_devices()
-        return cls.device_list
-
 class JobsDirOption(ConfigOption):
     @staticmethod
     def name():

digits/device_query.py

@@ -73,11 +73,17 @@ class CudaDeviceProp(ctypes.Structure):
             ('multiGpuBoardGroupID', ctypes.c_int),
             ]
 
+devices = None
+
 def get_devices():
     """
     Returns a list of CudaDeviceProp's
     Prints an error and returns None if something goes wrong
     """
+    global devices
+    if devices is not None:
+        # Only query CUDA once
+        return devices
     devices = []
 
     # Load library