Add in_ and at helpers to allow for directly requesting a retry (#130)

Closes #129

Author: bunchesofdonald

src/docket/dependencies.py

@@ -3,7 +3,7 @@
 import time
 from contextlib import AsyncExitStack, asynccontextmanager
 from contextvars import ContextVar
-from datetime import timedelta
+from datetime import datetime, timedelta, timezone
 from types import TracebackType
 from typing import (
     TYPE_CHECKING,
@@ -14,6 +14,7 @@
     Callable,
     Counter,
     Generic,
+    NoReturn,
     TypeVar,
     cast,
 )
@@ -188,6 +189,10 @@ async def my_task(logger: LoggerAdapter[Logger] = TaskLogger()) -> None:
     return cast(logging.LoggerAdapter[logging.Logger], _TaskLogger())
 
 
+class ForcedRetry(Exception):
+    """Raised when a task requests a retry via `in_` or `at`"""
+
+
 class Retry(Dependency):
     """Configures linear retries for a task.  You can specify the total number of
     attempts (or `None` to retry indefinitely), and the delay between attempts.
@@ -222,6 +227,17 @@ async def __aenter__(self) -> "Retry":
         retry.attempt = execution.attempt
         return retry
 
+    def at(self, when: datetime) -> NoReturn:
+        now = datetime.now(timezone.utc)
+        diff = when - now
+        diff = diff if diff.total_seconds() >= 0 else timedelta(0)
+
+        self.in_(diff)
+
+    def in_(self, when: timedelta) -> NoReturn:
+        self.delay: timedelta = when
+        raise ForcedRetry()
+
 
 class ExponentialRetry(Retry):
     """Configures exponential retries for a task.  You can specify the total number
@@ -251,22 +267,21 @@ def __init__(
             maximum_delay: The maximum delay between attempts.
         """
         super().__init__(attempts=attempts, delay=minimum_delay)
-        self.minimum_delay = minimum_delay
         self.maximum_delay = maximum_delay
 
     async def __aenter__(self) -> "ExponentialRetry":
         execution = self.execution.get()
 
         retry = ExponentialRetry(
             attempts=self.attempts,
-            minimum_delay=self.minimum_delay,
+            minimum_delay=self.delay,
             maximum_delay=self.maximum_delay,
         )
         retry.attempt = execution.attempt
 
         if execution.attempt > 1:
             backoff_factor = 2 ** (execution.attempt - 1)
-            calculated_delay = self.minimum_delay * backoff_factor
+            calculated_delay = self.delay * backoff_factor
 
             if calculated_delay > self.maximum_delay:
                 retry.delay = self.maximum_delay

tests/test_dependencies.py

@@ -1,9 +1,10 @@
 import logging
+from datetime import datetime, timedelta, timezone
 
 import pytest
 
 from docket import CurrentDocket, CurrentWorker, Docket, Worker
-from docket.dependencies import Depends, Retry, TaskArgument
+from docket.dependencies import Depends, ExponentialRetry, Retry, TaskArgument
 
 
 async def test_dependencies_may_be_duplicated(docket: Docket, worker: Worker):
@@ -95,6 +96,127 @@ async def the_task(
     assert calls == 2
 
 
+@pytest.mark.parametrize("retry_cls", [Retry, ExponentialRetry])
+async def test_user_can_request_a_retry_in_timedelta_time(
+    retry_cls: Retry, docket: Docket, worker: Worker
+):
+    calls = 0
+    first_call_time = None
+    second_call_time = None
+
+    async def the_task(
+        a: str,
+        b: str,
+        retry: Retry = retry_cls(attempts=2),  # type: ignore[reportCallIssue]
+    ):
+        assert a == "a"
+        assert b == "b"
+
+        nonlocal calls
+        calls += 1
+
+        nonlocal first_call_time
+        if not first_call_time:
+            first_call_time = datetime.now(timezone.utc)
+            retry.in_(timedelta(seconds=0.5))
+        else:
+            nonlocal second_call_time
+            second_call_time = datetime.now(timezone.utc)
+
+    await docket.add(the_task)("a", "b")
+
+    await worker.run_until_finished()
+
+    assert calls == 2
+
+    assert isinstance(first_call_time, datetime)
+    assert isinstance(second_call_time, datetime)
+
+    delay = second_call_time - first_call_time
+    assert delay.total_seconds() > 0 < 1
+
+
+@pytest.mark.parametrize("retry_cls", [Retry, ExponentialRetry])
+async def test_user_can_request_a_retry_at_a_specific_time(
+    retry_cls: Retry, docket: Docket, worker: Worker
+):
+    calls = 0
+    first_call_time = None
+    second_call_time = None
+
+    async def the_task(
+        a: str,
+        b: str,
+        retry: Retry = retry_cls(attempts=2),  # type: ignore[reportCallIssue]
+    ):
+        assert a == "a"
+        assert b == "b"
+
+        nonlocal calls
+        calls += 1
+
+        nonlocal first_call_time
+        if not first_call_time:
+            when = datetime.now(timezone.utc) + timedelta(seconds=0.5)
+            first_call_time = datetime.now(timezone.utc)
+            retry.at(when)
+        else:
+            nonlocal second_call_time
+            second_call_time = datetime.now(timezone.utc)
+
+    await docket.add(the_task)("a", "b")
+
+    await worker.run_until_finished()
+
+    assert calls == 2
+
+    assert isinstance(first_call_time, datetime)
+    assert isinstance(second_call_time, datetime)
+
+    delay = second_call_time - first_call_time
+    assert delay.total_seconds() > 0 < 1
+
+
+async def test_user_can_request_a_retry_at_a_specific_time_in_the_past(
+    docket: Docket, worker: Worker
+):
+    calls = 0
+    first_call_time = None
+    second_call_time = None
+
+    async def the_task(
+        a: str,
+        b: str,
+        retry: Retry = Retry(attempts=2),
+    ):
+        assert a == "a"
+        assert b == "b"
+
+        nonlocal calls
+        calls += 1
+
+        nonlocal first_call_time
+        if not first_call_time:
+            when = datetime.now(timezone.utc) - timedelta(days=1)
+            first_call_time = datetime.now(timezone.utc)
+            retry.at(when)
+        else:
+            nonlocal second_call_time
+            second_call_time = datetime.now(timezone.utc)
+
+    await docket.add(the_task)("a", "b")
+
+    await worker.run_until_finished()
+
+    assert calls == 2
+
+    assert isinstance(first_call_time, datetime)
+    assert isinstance(second_call_time, datetime)
+
+    delay = second_call_time - first_call_time
+    assert delay.total_seconds() > 0 < 1
+
+
 async def test_dependencies_error_for_missing_task_argument(
     docket: Docket, worker: Worker, caplog: pytest.LogCaptureFixture
 ):