Improve TimerTask

.flake8

@@ -1,5 +1,5 @@
 [flake8]
-ignore = E501,C901
+ignore = E501,C901,W503
 exclude = 
     .git
     *_pb2*

docs/supported-patterns.md

@@ -64,12 +64,12 @@ def purchase_order_workflow(ctx: task.OrchestrationContext, order: Order):
     # Orders of $1000 or more require manager approval
     yield ctx.call_activity(send_approval_request, input=order)
 
-    # Approvals must be received within 24 hours or they will be canceled.
+    # Approvals must be received within 24 hours or they will be cancelled.
     approval_event = ctx.wait_for_external_event("approval_received")
     timeout_event = ctx.create_timer(timedelta(hours=24))
     winner = yield task.when_any([approval_event, timeout_event])
     if winner == timeout_event:
-        return "Canceled"
+        return "Cancelled"
 
     # The order was approved
     yield ctx.call_activity(place_order, input=order)

durabletask-azuremanaged/durabletask/azuremanaged/worker.py

@@ -80,4 +80,6 @@ def __init__(self, *,
             log_handler=log_handler,
             log_formatter=log_formatter,
             interceptors=interceptors,
-            concurrency_options=concurrency_options)
+            concurrency_options=concurrency_options,
+            maximum_timer_interval=None  # DTS allows timers of indefinite length
+        )

durabletask/task.py

@@ -98,7 +98,7 @@ def set_custom_status(self, custom_status: Any) -> None:
         pass
 
     @abstractmethod
-    def create_timer(self, fire_at: Union[datetime, timedelta]) -> Task:
+    def create_timer(self, fire_at: Union[datetime, timedelta]) -> CancellableTask:
         """Create a Timer Task to fire after at the specified deadline.
 
         Parameters
@@ -228,10 +228,10 @@ def call_sub_orchestrator(self, orchestrator: Union[Orchestrator[TInput, TOutput
         """
         pass
 
-    # TOOD: Add a timeout parameter, which allows the task to be canceled if the event is
+    # TOOD: Add a timeout parameter, which allows the task to be cancelled if the event is
     # not received within the specified timeout. This requires support for task cancellation.
     @abstractmethod
-    def wait_for_external_event(self, name: str) -> CompletableTask:
+    def wait_for_external_event(self, name: str) -> CancellableTask:
         """Wait asynchronously for an event to be raised with the name `name`.
 
         Parameters
@@ -324,6 +324,10 @@ class OrchestrationStateError(Exception):
     pass
 
 
+class TaskCancelledError(Exception):
+    """Exception type for cancelled orchestration tasks."""
+
+
 class Task(ABC, Generic[T]):
     """Abstract base class for asynchronous tasks in a durable orchestration."""
     _result: T
@@ -435,6 +439,48 @@ def fail(self, message: str, details: Union[Exception, pb.TaskFailureDetails]):
             self._parent.on_child_completed(self)
 
 
+class CancellableTask(CompletableTask[T]):
+    """A completable task that can be cancelled before it finishes."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self._is_cancelled = False
+        self._cancel_handler: Optional[Callable[[], None]] = None
+
+    @property
+    def is_cancelled(self) -> bool:
+        """Returns True if the task was cancelled, False otherwise."""
+        return self._is_cancelled
+
+    def get_result(self) -> T:
+        if self._is_cancelled:
+            raise TaskCancelledError('The task was cancelled.')
+        return super().get_result()
+
+    def set_cancel_handler(self, cancel_handler: Callable[[], None]) -> None:
+        self._cancel_handler = cancel_handler
+
+    def cancel(self) -> bool:
+        """Attempts to cancel this task.
+
+        Returns
+        -------
+        bool
+            True if cancellation was applied, False if the task had already completed.
+        """
+        if self._is_complete:
+            return False
+
+        if self._cancel_handler is not None:
+            self._cancel_handler()
+
+        self._is_cancelled = True
+        self._is_complete = True
+        if self._parent is not None:
+            self._parent.on_child_completed(self)
+        return True
+
+
 class RetryableTask(CompletableTask[T]):
     """A task that can be retried according to a retry policy."""
 
@@ -474,13 +520,32 @@ def compute_next_delay(self) -> Optional[timedelta]:
         return None
 
 
-class TimerTask(CompletableTask[T]):
+class TimerTask(CancellableTask[None]):
+    def set_retryable_parent(self, retryable_task: RetryableTask):
+        self._retryable_parent = retryable_task
+
+    def complete(self, _: datetime) -> None:
+        super().complete(None)
 
-    def __init__(self) -> None:
+
+class LongTimerTask(TimerTask):
+    def __init__(self, final_fire_at: datetime, maximum_timer_interval: timedelta):
         super().__init__()
+        self._final_fire_at = final_fire_at
+        self._maximum_timer_interval = maximum_timer_interval
 
-    def set_retryable_parent(self, retryable_task: RetryableTask):
-        self._retryable_parent = retryable_task
+    def start(self, current_utc_datetime: datetime) -> datetime:
+        return self._get_next_fire_at(current_utc_datetime)
+
+    def complete(self, current_utc_datetime: datetime) -> Optional[datetime]:
+        if current_utc_datetime < self._final_fire_at:
+            return self._get_next_fire_at(current_utc_datetime)
+        return super().complete(current_utc_datetime)
+
+    def _get_next_fire_at(self, current_utc_datetime: datetime) -> datetime:
+        if current_utc_datetime + self._maximum_timer_interval < self._final_fire_at:
+            return current_utc_datetime + self._maximum_timer_interval
+        return self._final_fire_at
 
 
 class WhenAnyTask(CompositeTask[Task]):