imager: add proper handling of startup exceptions

scripts/main.py

@@ -120,9 +120,14 @@ if __name__ == "__main__":
     stepper_thread.start()
 
     # Starts the imager control process
-    logger.info("Starting the imager control process (step 3/4)")
-    imager_thread = planktoscope.imager.ImagerProcess(shutdown_event)
-    imager_thread.start()
+    logger.info("Starting the imager control process (step 3/6)")
+    try:
+        imager_thread = planktoscope.imager.ImagerProcess(shutdown_event)
+    except:
+        logger.error("The imager control process could not be started")
+        imager_thread = None
+    else:
+        imager_thread.start()
 
     # Starts the segmenter process
     logger.info("Starting the segmenter control process (step 4/4)")
@@ -148,7 +153,7 @@ if __name__ == "__main__":
         if not stepper_thread.is_alive():
             logger.error("The stepper process died unexpectedly! Oh no!")
             break
-        if not imager_thread.is_alive():
+        if imager_thread and not imager_thread.is_alive():
             logger.error("The imager process died unexpectedly! Oh no!")
             break
         if not segmenter_thread.is_alive():
@@ -160,12 +165,14 @@ if __name__ == "__main__":
     shutdown_event.set()
     time.sleep(1)
     stepper_thread.join()
-    imager_thread.join()
+    if imager_thread:
+        imager_thread.join()
     segmenter_thread.join()
     # Uncomment this for clean shutdown
     # module_thread.join()
     stepper_thread.close()
-    imager_thread.close()
+    if imager_thread:
+        imager_thread.close()
     segmenter_thread.close()
     # Uncomment this for clean shutdown
     # module_thread.close()

scripts/planktoscope/imager.py

@@ -93,7 +93,7 @@ class StreamingHandler(http.server.BaseHTTPRequestHandler):
             try:
                 while True:
                     try:
-                        with open("/dev/shm/mjpeg/cam.jpg", "rb") as jpeg:
+                        with open("/dev/shm/mjpeg/cam.jpg", "rb") as jpeg:  # nosec
                             frame = jpeg.read()
                     except FileNotFoundError as e:
                         logger.error(f"Camera has not been started yet")
@@ -129,7 +129,6 @@ logger.info("planktoscope.imager is loaded")
 class ImagerProcess(multiprocessing.Process):
     """This class contains the main definitions for the imager of the PlanktoScope"""
 
-    @logger.catch
     def __init__(self, stop_event, iso=100, shutter_speed=1):
         """Initialize the Imager class
 
@@ -179,7 +178,14 @@ class ImagerProcess(multiprocessing.Process):
             logger.exception(
                 f"An exception has occured when starting up raspimjpeg: {e}"
             )
-            exit(1)
+            try:
+                self.__camera.start(true)
+            except Exception as e:
+                logger.exception(
+                    f"A second exception has occured when starting up raspimjpeg: {e}"
+                )
+                logger.error(f"This error can't be recovered from, terminating now")
+                raise e
 
         if self.__camera.sensor_name == "IMX219":  # Camera v2.1
             self.__resolution = (3280, 2464)
@@ -653,7 +659,7 @@ class ImagerProcess(multiprocessing.Process):
             return
 
         logger.debug(f"Copying the image from the temp file to {filename_path}")
-        shutil.copy("/dev/shm/mjpeg/image.jpg", filename_path)
+        shutil.copy("/dev/shm/mjpeg/image.jpg", filename_path)  # nosec
         # TODO Try to stop the camera streaming and display instead each captured image
         # os.rename("/dev/shm/mjpeg/image.jpg", "/dev/shm/mjpeg/cam.jpg")
         logger.debug("Syncing the disk")
@@ -792,4 +798,4 @@ class ImagerProcess(multiprocessing.Process):
 # This is called if this script is launched directly
 if __name__ == "__main__":
     # TODO This should be a test suite for this library
-    pass
+    pass