Partial fix to the cancel method

experiment.py

@@ -45,11 +45,11 @@ async def main():
     print("Spawning countdown immediately, scheduling count for 4 secs from now")
     task = loop.spawn(countdown(8))
     task1 = loop.schedule(count(8, 2), 4)   # Schedules the task, it will be ran 4 seconds from now
-    await giambio.sleep(0)  # Act as a checkpoint to switch tasks. Beware! Cancelling a task straight away will propagate the error in the parent
+    await giambio.sleep(0)  # TODO: Fix this to avoid the need to use a checkpoint before cancelling
-#    await task.cancel()    # TODO: Fix this to reschedule the parent task properly
+    await task.cancel()
-    result = await task.join()
+#    result = await task.join()  # Would raise TaskError!
     result1 = await task1.join()
-    print(f"countdown returned: {result}\ncount returned: {result1}")
+    print(f"countdown returned: {None}\ncount returned: {result1}")
     print("All done")
 
 loop.start(main)

giambio/abstractions.py

@@ -1,5 +1,5 @@
 import types
-
+from .traps import join, sleep, want_read, want_write, cancel
 
 class Result:
     """A wrapper for results of coroutines"""

giambio/core.py

@@ -7,9 +7,9 @@ from .exceptions import AlreadyJoinedError, CancelledError
 from timeit import default_timer
 from time import sleep as wait
 from .socket import AsyncSocket, WantRead, WantWrite
-from .traps import join, sleep, want_read, want_write, cancel
 from .abstractions import Task, Result
 from socket import SOL_SOCKET, SO_ERROR
+from .traps import join, sleep, want_read, want_write, cancel
 
 class EventLoop:
 
@@ -53,7 +53,7 @@ class EventLoop:
                     self.running.result = Result(e.args[0] if e.args else None, None)  # Saves the return value
                     self.to_run.extend(self.joined.pop(self.running, ()))  # Reschedules the parent task
                 except RuntimeError:
-                    self.to_run.extend(self.joined.pop(self.running, ()))
+                    self.to_run.extend(self.joined.pop(self.running, ()))   # Reschedules the parent task
                     self.to_run.append(self.running)
                 except Exception as has_raised:
                     self.to_run.extend(self.joined.pop(self.running, ()))  # Reschedules the parent task
@@ -116,8 +116,6 @@ class EventLoop:
         await want_read(sock)
         return sock.accept()
 
-
-
     async def sock_sendall(self, sock: socket.socket, data: bytes):
         """Sends all the passed data, as bytes, trough the socket asynchronously"""
 
@@ -151,11 +149,11 @@ class EventLoop:
             self.to_run.append(self.running)    # Reschedule the task that called sleep
 
     def want_cancel(self, task):
-        self.to_run.extend(self.joined.pop(self.running, ()))  # Reschedules the parent task
         task.cancelled = True
+        self.to_run.extend(self.joined.pop(self.running, ()))
+        self.to_run.append(self.running)   # Reschedules the parent task
         task.throw(CancelledError())
 
-
     async def connect_sock(self, sock: socket.socket, addr: tuple):
         try:			# "Borrowed" from curio
             result = sock.connect(addr)

giambio/exceptions.py

@@ -12,3 +12,6 @@ class CancelledError(GiambioError):
 
     def __repr__(self):
         return "giambio.exceptions.CancelledError"
+
+class TaskCancelled(GiambioError):
+    """This exception is raised when the user attempts to join a cancelled task"""

giambio/traps.py

@@ -2,8 +2,7 @@
 
 import types
 import socket
-from .abstractions import Task
+from .exceptions import TaskCancelled
-
 
 @types.coroutine
 def sleep(seconds: int):
@@ -35,16 +34,18 @@ def want_write(sock: socket.socket):
 
 
 @types.coroutine
-def join(task: Task):
+def join(task):
     """'Tells' the scheduler that the desired task MUST be awaited for completion"""
 
+    if task.cancelled:
+        raise TaskCancelled("Cannot join cancelled task!")
     task.joined = True
     yield "want_join", task
     return task.get_result()    # This raises an exception if the child task errored
 
 
 @types.coroutine
-def cancel(task: Task):
+def cancel(task):
     """'Tells' the scheduler that the passed task must be cancelled"""
 
     yield "want_cancel", task

test.py

@@ -3,7 +3,6 @@ from giambio.socket import AsyncSocket
 import socket
 import logging
 
-
 loop = giambio.core.EventLoop()
 
 logging.basicConfig(level=20,