Add singleton protection

sense_hat/sense_hat.py

@@ -12,6 +12,7 @@
 import pwd
 import array
 import fcntl
+import threading
 from PIL import Image  # pillow
 from copy import deepcopy
 
@@ -20,7 +21,10 @@
 from .exceptions import ColourSensorInitialisationError
 
 class SenseHat(object):
-
+    # singleton registration variables
+    _instance = None
+    _lock = threading.Lock()
+
     SENSE_HAT_FB_NAME = 'RPi-Sense FB'
     SENSE_HAT_FB_FBIOGET_GAMMA = 61696
     SENSE_HAT_FB_FBIOSET_GAMMA = 61697
@@ -30,6 +34,14 @@ class SenseHat(object):
     SENSE_HAT_FB_GAMMA_USER = 2
     SETTINGS_HOME_PATH = '.config/sense_hat'
 
+    # Ensure that there is only a single SenseHat object running to prevent sensor read issues
+    def __new__(cls):
+        if cls._instance is None:
+            with cls._lock:
+                if not cls._instance:
+                    cls._instance = super().__new__(cls)
+        return cls._instance
+
     def __init__(
             self,
             imu_settings_file='RTIMULib',

tests/test_singleton.py

@@ -0,0 +1,33 @@
+from sense_hat import SenseHat
+import unittest
+import time
+import concurrent.futures
+
+
+def get_temp(dummy):
+    sense = SenseHat()
+    time.sleep(5)
+    print(dummy)
+    return round(sense.get_temperature())
+
+class TestSingleton(unittest.TestCase):
+    def test_singleton(self):
+        sense1 = SenseHat()
+        sense2 = SenseHat()
+        self.assertEqual(sense1.get_temperature(), sense2.get_temperature())    
+        self.assertEqual(sense1, sense2)
+
+    @unittest.expectedFailure   
+    def test_multiprocess(self):
+        executions = ["run1", "run2", "run3", "run4", "run5"]
+        prev_temp = None
+        with concurrent.futures.ProcessPoolExecutor() as executor:
+            for temp in executor.map(get_temp,executions):
+                if prev_temp:
+                    print(prev_temp, temp)
+                    self.assertEqual(temp, prev_temp)
+                prev_temp = temp    
+
+
+if __name__ == "__main__":
+    unittest.main()