SingleInstanceTask: add cancel_restart
cancel_restart is a mode for SingleInstanceTask that changes the behavior when starting the task - if the task is already running, do not cancel it to start another.
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@ -48,12 +48,21 @@ async def run_in_thread(func, *args):
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raise asyncio.CancelledError
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class TaskAlreadyRunningError(Exception):
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"""Used to let callers know that a task hasn't been started due to
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cancel_restart == False and the task already running."""
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pass
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class SingleInstanceTask:
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def __init__(self, func, propagate_errors=True):
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def __init__(self, func, propagate_errors=True, cancel_restart=True):
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self.func = func
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self.propagate_errors = propagate_errors
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self.task = None
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# if True, allow subsequent start calls to cancel a running task
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# raises TaskAlreadyRunningError if we skip starting the task.
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self.cancel_restart = cancel_restart
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async def _start(self, old):
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if old is not None:
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@ -69,6 +78,10 @@ class SingleInstanceTask:
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return self.task
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def start_sync(self, *args, **kw):
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if not self.cancel_restart:
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if self.task is not None and not self.task.done():
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raise TaskAlreadyRunningError(
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'Skipping invocation of task - already running')
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old = self.task
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coro = self.func(*args, **kw)
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if asyncio.iscoroutine(coro):
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@ -0,0 +1,47 @@
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# Copyright 2022 Canonical, Ltd.
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as
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# published by the Free Software Foundation, either version 3 of the
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# License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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import asyncio
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import unittest
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from unittest.mock import AsyncMock
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from parameterized import parameterized
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from subiquitycore.async_helpers import (
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SingleInstanceTask,
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TaskAlreadyRunningError,
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)
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class TestSingleInstanceTask(unittest.IsolatedAsyncioTestCase):
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@parameterized.expand([(True, 2), (False, 1)])
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async def test_cancellable(self, cancel_restart, expected_call_count):
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async def fn():
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await asyncio.sleep(3)
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raise Exception('timeout')
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mock_fn = AsyncMock(side_effect=fn)
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sit = SingleInstanceTask(mock_fn, cancel_restart=cancel_restart)
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await sit.start()
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await asyncio.sleep(.01)
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try:
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await sit.start()
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except TaskAlreadyRunningError:
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restarted = False
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else:
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restarted = True
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sit.task.cancel()
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self.assertEqual(expected_call_count, mock_fn.call_count)
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self.assertEqual(cancel_restart, restarted)
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