Various fixes, check experiment.py file

experiment.py

@@ -4,18 +4,26 @@ loop = giambio.EventLoop()
 
 """
 
-What works and what does not (25th March 2020 20:35)
+What works and what does not (5 Apr 2020 12:06 AM):
 
 - Run tasks concurrently: V
 - Join mechanism: V
 - Sleep mechanism: V
 - Cancellation mechanism: V
-- Exception propagation: X
+- Exception propagation: X   Note: Almost ready
 - Concurrent I/O: V
 - Return values of coroutines: V
 - Scheduling tasks for future execution: V
 - Task Spawner (context manager): V
 
+
+What's left to implement:
+
+- An event system to wake up tasks programmatically
+- Lower-level primitives such as locks, queues, semaphores
+- File I/O (Also, consider that Windows won't allow select to work on non-socket fds)
+- Complete the AsyncSocket implementation (happy eyeballs, other methods)
+- Debugging tools
 """
 
 async def countdown(n):
@@ -43,16 +51,22 @@ async def count(stop, step=1):
         return "Count UP over"
     except giambio.CancelledError:
         print("count cancelled!")
-
+#        raise BaseException      # This will propagate
 
 async def main():
+    try:
         print("Spawning countdown immediately, scheduling count for 4 secs from now")
         async with giambio.TaskManager(loop) as manager:
             task = manager.spawn(countdown(8))
-            manager.schedule(count(8, 2), 4)
+            task2 = manager.schedule(count(8, 2), 4)
+            await task.cancel()   # This works, but other tasks continue running
         for task, ret in manager.values.items():
             print(f"Function '{task.coroutine.__name__}' at {hex(id(task.coroutine))} returned an object of type '{type(ret).__name__}': {repr(ret)}")
+    except Exception as e:
+        print(f"Actually I prefer to catch it here: {e}")  # Everything works just as expected, the try/except block below won't trigger
 
 
-loop.start(main)
-
+try:
+    loop.start(main)
+except Exception:      # Exceptions climb the whole stack
+    print("Exceptions propagate!")

giambio/traps.py

@@ -74,4 +74,3 @@ def _cancel(task):
 
     task.cancelled = True
     yield "want_cancel", task
-

giambio/util.py

@@ -17,10 +17,14 @@ class TaskManager:
 
 
     async def _cancel_and_raise(self, exc):
-        self.loop._exiting = True   # Tells the loop not to catch all exceptions
-        for task in self.tasks:
-            await task.cancel()
-        raise exc
+        if not isinstance(exc, CancelledError):
+            self.loop._exiting = True   # Tells the loop not to catch all exceptions
+            try:
+                for task in self.tasks:
+                    await task.cancel()
+            except Exception:
+                pass
+            raise exc
 
     async def __aenter__(self):
         return self
@@ -30,8 +34,7 @@ class TaskManager:
             task = self.tasks.popleft()
             self.values[task] = await task.join()
             if task.result.exc:
-                if task.result.exc != CancelledError:
-                    await self._cancel_and_raise(task.result.exc)
+                await self._cancel_and_raise(task.result.exc)
 
     def spawn(self, coroutine: types.coroutine):
         """Schedules a task for execution, appending it to the call stack"""