Delay_ms: trig after deinit raises exception.

Author: peterhinch

v3/docs/TUTORIAL.md

@@ -43,6 +43,7 @@ REPL.
        4.1.2 [Portable code](./TUTORIAL.md#412-portable-code)  
   4.2 [Asynchronous iterators](./TUTORIAL.md#42-asynchronous-iterators)  
   4.3 [Asynchronous context managers](./TUTORIAL.md#43-asynchronous-context-managers)  
+  4.4 [Object scope](./TUTORIAL.md#44-object-scope) What happens when an object goes out of scope.  
  5. [Exceptions timeouts and cancellation](./TUTORIAL.md#5-exceptions-timeouts-and-cancellation)  
   5.1 [Exceptions](./TUTORIAL.md#51-exceptions)  
        5.1.1 [Global exception handler](./TUTORIAL.md#511-global-exception-handler)  
@@ -1134,7 +1135,7 @@ Methods:
  proceed when the instance has timed out.
  7. `callback` args `func=None`, `args=()`. Allows the callable and its args to
  be assigned, reassigned or disabled at run time.
- 8. `deinit` No args. Cancels the coroutine.
+ 8. `deinit` No args. Cancels the running task. See [Object scope](./TUTORIAL.md#44-object-scope).
 
 In this example a `Delay_ms` instance is created with the default duration of
 1s. It is repeatedly triggered for 5 secs, preventing the callback from
@@ -1522,6 +1523,16 @@ asyncio.run(bar())
 
 ###### [Contents](./TUTORIAL.md#contents)
 
+## 4.4 Object scope
+
+If an object launches a task and that object goes out of scope, the task will
+continue to be scheduled. The task will run to completion or until cancelled.
+If this is undesirable consider writing a `deinit` method to cancel associated
+running tasks. Applications can call `deinit`, for example in a `try...finally`
+block or in a context manager.
+
+###### [Contents](./TUTORIAL.md#contents)
+
 # 5 Exceptions timeouts and cancellation
 
 These topics are related: `uasyncio` enables the cancellation of tasks, and the

v3/primitives/delay_ms.py

@@ -48,6 +48,8 @@ async def _timer(self, dt):
 # API
     # trigger may be called from hard ISR.
     def trigger(self, duration=0):  # Update absolute end time, 0-> ctor default
+        if self._mtask is None:
+            raise RuntimeError("Delay_ms.deinit() has run.")
         self._tend = ticks_add(ticks_ms(), duration if duration > 0 else self._durn)
         self._retn = None  # Default in case cancelled.
         self._busy = True
@@ -73,3 +75,4 @@ def callback(self, func=None, args=()):
     def deinit(self):
         self.stop()
         self._mtask.cancel()
+        self._mtask = None

v3/primitives/tests/delay_test.py

@@ -91,6 +91,7 @@ async def reduce_test():  # Test reducing a running delay
 Callback should run
 cb callback
 Callback should run
+cb callback
 Done
 '''
     printexp(s, 11)
@@ -174,6 +175,31 @@ def timer_cb(_):
     await asyncio.sleep(1)
     print('Done')
 
+async def err_test():  # Test triggering de-initialised timer
+    s = '''
+Running (runtime = 3s):
+Trigger 1 sec delay
+cb callback
+Success: error was raised.
+Done
+    '''
+    printexp(s, 3)
+    def cb(v):
+        print('cb', v)
+        return 42
+
+    d = Delay_ms(cb, ('callback',))
+
+    print('Trigger 1 sec delay')
+    d.trigger(1000)
+    await asyncio.sleep(2)
+    d.deinit()
+    try:
+        d.trigger(1000)
+    except RuntimeError:
+        print("Success: error was raised.")
+    print('Done')
+
 av = '''
 Run a test by issuing
 delay_test.test(n)
@@ -184,11 +210,12 @@ def timer_cb(_):
 2 Test reducing the duration of a running timer
 3 Test delay defined by constructor arg
 4 Test triggering a Task
+5 Attempt to trigger de-initialised instance
 \x1b[39m
 '''
 print(av)
 
-tests = (isr_test, stop_test, reduce_test, ctor_test, launch_test)
+tests = (isr_test, stop_test, reduce_test, ctor_test, launch_test, err_test)
 def test(n=0):
     try:
         asyncio.run(tests[n]())