feat: add simple background_task and io_bound functions

learning_loop_node/helpers/background_tasks.py

@@ -0,0 +1,78 @@
+# Copy of Nicegui background_tasks.py
+# MIT License
+
+# Copyright (c) 2021 Zauberzeug GmbH
+
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+"""inspired from https://quantlane.com/blog/ensure-asyncio-task-exceptions-get-logged/"""
+from __future__ import annotations
+
+import asyncio
+import logging
+from typing import Awaitable, Dict, Set
+
+running_tasks: Set[asyncio.Task] = set()
+lazy_tasks_running: Dict[str, asyncio.Task] = {}
+lazy_tasks_waiting: Dict[str, Awaitable] = {}
+
+
+def create(coroutine: Awaitable, *, name: str = 'unnamed task') -> asyncio.Task:
+    """Wraps a loop.create_task call and ensures there is an exception handler added to the task.
+
+    If the task raises an exception, it is logged and handled by the global exception handlers.
+    Also a reference to the task is kept until it is done, so that the task is not garbage collected mid-execution.
+    See https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task.
+    """
+    loop = asyncio.get_event_loop()
+    coroutine = coroutine if asyncio.iscoroutine(coroutine) else asyncio.wait_for(coroutine, None)
+    task: asyncio.Task = loop.create_task(coroutine, name=name)
+    task.add_done_callback(_handle_task_result)
+    running_tasks.add(task)
+    task.add_done_callback(running_tasks.discard)
+    return task
+
+
+def create_lazy(coroutine: Awaitable, *, name: str) -> None:
+    """Wraps a create call and ensures a second task with the same name is delayed until the first one is done.
+
+    If a third task with the same name is created while the first one is still running, the second one is discarded.
+    """
+    if name in lazy_tasks_running:
+        if name in lazy_tasks_waiting:
+            asyncio.Task(lazy_tasks_waiting[name]).cancel()
+        lazy_tasks_waiting[name] = coroutine
+        return
+
+    def finalize(name: str) -> None:
+        lazy_tasks_running.pop(name)
+        if name in lazy_tasks_waiting:
+            create_lazy(lazy_tasks_waiting.pop(name), name=name)
+    task = create(coroutine, name=name)
+    lazy_tasks_running[name] = task
+    task.add_done_callback(lambda _: finalize(name))
+
+
+def _handle_task_result(task: asyncio.Task) -> None:
+    try:
+        task.result()
+    except asyncio.CancelledError:
+        pass
+    except Exception:
+        logging.exception('Background task %s raised an exception', task.get_name())

learning_loop_node/helpers/run.py

@@ -0,0 +1,12 @@
+import asyncio
+from typing import Callable, ParamSpec, TypeVar
+
+T = TypeVar('T')
+P = ParamSpec('P')
+
+
+async def io_bound(func: Callable[P, T], *args: P.args, **kwargs: P.kwargs) -> T:
+    """Run a blocking function in a thread pool executor.
+    This is useful for disk I/O operations that would block the event loop."""
+    loop = asyncio.get_event_loop()
+    return await loop.run_in_executor(None, lambda: func(*args, **kwargs))