NotifierDelay: Defensively free the notifier

Allow for using a NotifierDelay as a context manager.
Also add a __del__ to doubly ensure this is cleaned up, similarly to
Python's IO objects.

Author: auscompgeek

magicbot/magicrobot.py

@@ -295,30 +295,26 @@ def disabled(self):
         ds_attached = None
         wpilib.LiveWindow.setEnabled(False)
 
-        delay = NotifierDelay(self.control_loop_wait_time)
-
         self._on_mode_disable_components()
         try:
             self.disabledInit()
         except:
             self.onException(forceReport=True)
 
-        while self.isDisabled():
-            
-            if ds_attached != self.ds.isDSAttached():
-                ds_attached = not ds_attached
-                self.__nt.putBoolean('is_ds_attached', ds_attached)
-            
-            try:
-                self.disabledPeriodic()
-            except:
-                self.onException()
+        with NotifierDelay(self.control_loop_wait_time) as delay:
+            while self.isDisabled():
+                if ds_attached != self.ds.isDSAttached():
+                    ds_attached = not ds_attached
+                    self.__nt.putBoolean('is_ds_attached', ds_attached)
 
-            self._update_feedback()
-            self.robotPeriodic()
-            delay.wait()
+                try:
+                    self.disabledPeriodic()
+                except:
+                    self.onException()
 
-        delay.free()
+                self._update_feedback()
+                self.robotPeriodic()
+                delay.wait()
 
     def operatorControl(self):
         """
@@ -335,8 +331,6 @@ def operatorControl(self):
         self.__nt.putBoolean('is_ds_attached', self.ds.isDSAttached())
         wpilib.LiveWindow.setEnabled(False)
 
-        delay = NotifierDelay(self.control_loop_wait_time)
-
         # initialize things
         self._on_mode_enable_components()
 
@@ -345,20 +339,19 @@ def operatorControl(self):
         except:
             self.onException(forceReport=True)
 
-        while self.isOperatorControl() and self.isEnabled():
-            
-            try:
-                self.teleopPeriodic()
-            except:
-                self.onException()
+        with NotifierDelay(self.control_loop_wait_time) as delay:
+            while self.isOperatorControl() and self.isEnabled():
+                try:
+                    self.teleopPeriodic()
+                except:
+                    self.onException()
 
-            self._execute_components()
-            self._update_feedback()
-            self.robotPeriodic()
+                self._execute_components()
+                self._update_feedback()
+                self.robotPeriodic()
 
-            delay.wait()
+                delay.wait()
 
-        delay.free()
         self._on_mode_disable_components()
 
     def test(self):
@@ -368,24 +361,21 @@ def test(self):
         self.__nt.putBoolean('is_ds_attached', self.ds.isDSAttached())
         wpilib.LiveWindow.setEnabled(True)
 
-        delay = NotifierDelay(self.control_loop_wait_time)
-
         try:
             self.testInit()
         except:
             self.onException(forceReport=True)
-        
-        while self.isTest() and self.isEnabled():
-            try:
-                self.testPeriodic()
-            except:
-                self.onException()
 
-            self._update_feedback()
-            self.robotPeriodic()
-            delay.wait()
+        with NotifierDelay(self.control_loop_wait_time) as delay:
+            while self.isTest() and self.isEnabled():
+                try:
+                    self.testPeriodic()
+                except:
+                    self.onException()
 
-        delay.free()
+                self._update_feedback()
+                self.robotPeriodic()
+                delay.wait()
 
     def _on_mode_enable_components(self):
         # initialize things

robotpy_ext/autonomous/selector.py

@@ -226,24 +226,22 @@ def run(self, control_loop_wait_time=0.020, iter_fn=None, on_exception=None):
         #
         # Autonomous control loop
         #
-        
-        delay = NotifierDelay(control_loop_wait_time)
-        
-        while self.ds.isAutonomous() and self.ds.isEnabled():
- 
-            try:            
-                self._on_iteration(timer.get())
-            except:
-                on_exception()
-            
-            if isinstance(iter_fn, (list, tuple)):
-                for fn in iter_fn:
-                    fn()
-            else:
-                iter_fn()
-             
-            delay.wait()
-            
+
+        with NotifierDelay(control_loop_wait_time) as delay:
+            while self.ds.isAutonomous() and self.ds.isEnabled():
+                try:
+                    self._on_iteration(timer.get())
+                except:
+                    on_exception()
+
+                if isinstance(iter_fn, (list, tuple)):
+                    for fn in iter_fn:
+                        fn()
+                else:
+                    iter_fn()
+
+                delay.wait()
+
         #
         # Done with autonomous, finish up
         #

robotpy_ext/misc/precise_delay.py

@@ -85,6 +85,13 @@ class NotifierDelay:
     This will delay so that the next invocation of your loop happens at
     precisely the same period, assuming that your loop does not take longer
     than the specified period.
+
+    Example::
+
+        with NotifierDelay(0.02) as delay:
+            while something:
+                # do things here
+                delay.wait()
     """
 
     def __init__(self, delay_period: float) -> None:
@@ -100,15 +107,26 @@ def __init__(self, delay_period: float) -> None:
 
         wpilib.Resource._add_global_resource(self)
 
+    def __del__(self):
+        self.free()
+
+    def __enter__(self) -> 'NotifierDelay':
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.free()
+
     def free(self) -> None:
         """Clean up the notifier.
 
-        Call this method once you are done using this object.
         Do not use this object after this method is called.
         """
         handle = self._notifier
+        if handle is None:
+            return
         hal.stopNotifier(handle)
         hal.cleanNotifier(handle)
+        self._notifier = None
 
     def wait(self) -> None:
         """Wait until the delay period has passed."""