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drastically simplified meta-task internals

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Daniil Fajnberg
2022-03-26 10:49:32 +01:00
parent 0e7e92a91b
commit 54e5bfa8a0
2 changed files with 60 additions and 135 deletions
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src/asyncio_taskpool/pool.py
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@ -31,15 +31,13 @@ import logging
from asyncio.coroutines import iscoroutine, iscoroutinefunction
from asyncio.exceptions import CancelledError
from asyncio.locks import Semaphore
from asyncio.queues import QueueEmpty
from asyncio.tasks import Task, create_task, gather
from contextlib import suppress
from datetime import datetime
from math import inf
from typing import Any, Awaitable, Dict, Iterable, Iterator, List, Set, Union
from typing import Any, Awaitable, Dict, Iterable, List, Set, Union
from . import exceptions
from .queue_context import Queue
from .internals.constants import DEFAULT_TASK_GROUP, DATETIME_FORMAT
from .internals.group_register import TaskGroupRegister
from .internals.helpers import execute_optional, star_function
@ -491,8 +489,6 @@ class TaskPool(BaseTaskPool):
Adding tasks blocks **only if** the pool is full at that moment.
"""
_QUEUE_END_SENTINEL = object()
def __init__(self, pool_size: int = inf, name: str = None) -> None:
super().__init__(pool_size=pool_size, name=name)
# In addition to all the attributes of the base class, we need a dictionary mapping task group names to sets of
@ -714,34 +710,6 @@ class TaskPool(BaseTaskPool):
await task
return group_name
@classmethod
async def _queue_producer(cls, arg_queue: Queue, arg_iter: Iterator[Any], group_name: str) -> None:
"""
Keeps the arguments queue from :meth:`_map` full as long as the iterator has elements.
Intended to be run as a meta task of a specific group.
Args:
arg_queue: The queue of function arguments to consume for starting a new task.
arg_iter: The iterator of function arguments to put into the queue.
group_name: Name of the task group associated with this producer.
"""
try:
for arg in arg_iter:
await arg_queue.put(arg) # This blocks as long as the queue is full.
except CancelledError:
# This means that no more tasks are supposed to be created from this `_map()` call;
# thus, we can immediately drain the entire queue and forget about the rest of the arguments.
log.debug("Cancelled consumption of argument iterable in task group '%s'", group_name)
while True:
try:
arg_queue.get_nowait()
arg_queue.item_processed()
except QueueEmpty:
return
finally:
await arg_queue.put(cls._QUEUE_END_SENTINEL)
@staticmethod
def _get_map_end_callback(map_semaphore: Semaphore, actual_end_callback: EndCB) -> EndCB:
"""Returns a wrapped `end_callback` for each :meth:`_queue_consumer` task that releases the `map_semaphore`."""
@ -750,23 +718,25 @@ class TaskPool(BaseTaskPool):
await execute_optional(actual_end_callback, args=(task_id,))
return release_callback
async def _queue_consumer(self, arg_queue: Queue, group_name: str, func: CoroutineFunc, arg_stars: int = 0,
end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
async def _arg_consumer(self, group_name: str, group_size: int, func: CoroutineFunc, arg_iter: ArgsT,
arg_stars: int, end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
"""
Consumes arguments from the queue from :meth:`_map` and keeps a limited number of tasks working on them.
Consumes arguments from :meth:`_map` and keeps a limited number of tasks working on them.
The queue's maximum size is taken as the limiting value of an internal semaphore, which must be acquired before
a new task can be started, and which must be released when one of these tasks ends.
The `group_size` acts as the limiting value of an internal semaphore, which must be acquired before a new task
can be started, and which must be released when one of these tasks ends.
Intended to be run as a meta task of a specific group.
Args:
arg_queue:
The queue of function arguments to consume for starting a new task.
group_name:
Name of the associated task group; passed into :meth:`_start_task`.
group_size:
The maximum number new tasks spawned by this method to run concurrently.
func:
The coroutine function to use for spawning the new tasks within the task pool.
arg_iter:
The iterable of arguments; each element is to be passed into a `func` call when spawning a new task.
arg_stars (optional):
Whether or not to unpack an element from `arg_queue` using stars; must be 0, 1, or 2.
end_callback (optional):
@ -776,29 +746,27 @@ class TaskPool(BaseTaskPool):
The callback that was specified to execute after cancellation of the task (and the next one).
It is run with the task's ID as its only positional argument.
"""
map_semaphore = Semaphore(arg_queue.maxsize) # value determined by `group_size` in :meth:`_map`
map_semaphore = Semaphore(group_size)
release_cb = self._get_map_end_callback(map_semaphore, actual_end_callback=end_callback)
while True:
# The following line blocks **only if** the number of running tasks spawned by this method has reached the
# specified maximum as determined in :meth:`_map`.
for next_arg in arg_iter:
# When the number of running tasks spawned by this method reaches the specified maximum,
# this next line will block, until one of them ends and releases the semaphore.
await map_semaphore.acquire()
# We await the queue's `get()` coroutine and ensure that its `item_processed()` method is called.
async with arg_queue as next_arg:
if next_arg is self._QUEUE_END_SENTINEL:
# The :meth:`_queue_producer` either reached the last argument or was cancelled.
return
try:
await self._start_task(star_function(func, next_arg, arg_stars=arg_stars), group_name=group_name,
ignore_lock=True, end_callback=release_cb, cancel_callback=cancel_callback)
except CancelledError:
map_semaphore.release()
return
except Exception as e:
# This means an exception occurred during task **creation**, meaning no task has been created.
# It does not imply an error within the task itself.
log.exception("%s occurred while trying to create task: %s(%s%s)",
str(e.__class__.__name__), func.__name__, '*' * arg_stars, str(next_arg))
map_semaphore.release()
try:
await self._start_task(star_function(func, next_arg, arg_stars=arg_stars), group_name=group_name,
ignore_lock=True, end_callback=release_cb, cancel_callback=cancel_callback)
except CancelledError:
# This means that no more tasks are supposed to be created from this `arg_iter`;
# thus, we can forget about the rest of the arguments.
log.debug("Cancelled consumption of argument iterable in task group '%s'", group_name)
map_semaphore.release()
return
except Exception as e:
# This means an exception occurred during task **creation**, meaning no task has been created.
# It does not imply an error within the task itself.
log.exception("%s occurred while trying to create task: %s(%s%s)",
str(e.__class__.__name__), func.__name__, '*' * arg_stars, str(next_arg))
map_semaphore.release()
async def _map(self, group_name: str, group_size: int, func: CoroutineFunc, arg_iter: ArgsT, arg_stars: int,
end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
@ -815,11 +783,9 @@ class TaskPool(BaseTaskPool):
of the pool never imposes a limit, this ensures that the number of tasks belonging to this group and running
concurrently is always equal to `group_size` (except for when `arg_iter` is exhausted of course).
This method sets up an internal arguments queue which is continuously filled while consuming the `arg_iter`.
Because this method delegates the spawning of the tasks to two meta tasks (a producer and a consumer of the
aforementioned queue), it **never blocks**. However, just because this method returns immediately, this does
not mean that any task was started or that any number of tasks will start soon, as this is solely determined by
the :attr:`BaseTaskPool.pool_size` and the `group_size`.
Because this method delegates the spawning of the tasks to a meta task, it **never blocks**. However, just
because this method returns immediately, this does not mean that any task was started or that any number of
tasks will start soon, as this is solely determined by the :attr:`BaseTaskPool.pool_size` and the `group_size`.
Args:
group_name:
@ -850,17 +816,9 @@ class TaskPool(BaseTaskPool):
raise exceptions.InvalidGroupName(f"Group named {group_name} already exists!")
self._task_groups[group_name] = group_reg = TaskGroupRegister()
async with group_reg:
# Set up internal arguments queue. We limit its maximum size to enable lazy consumption of `arg_iter` by the
# `_queue_producer()`; that way an argument
# TODO: Perhaps this can be simplified to just one meta-task with no need for a queue.
# The limiting factor honoring the group size is already the semaphore in the queue consumer;
# Try to write this without a producer, instead consuming the `arg_iter` directly.
arg_queue = Queue(maxsize=group_size)
meta_tasks = self._group_meta_tasks_running.setdefault(group_name, set())
# Start the producer and consumer meta tasks.
meta_tasks.add(create_task(self._queue_producer(arg_queue, iter(arg_iter), group_name)))
meta_tasks.add(create_task(self._queue_consumer(arg_queue, group_name, func, arg_stars,
end_callback, cancel_callback)))
meta_tasks.add(create_task(self._arg_consumer(group_name, group_size, func, arg_iter, arg_stars,
end_callback=end_callback, cancel_callback=cancel_callback)))
async def map(self, func: CoroutineFunc, arg_iter: ArgsT, group_size: int = 1, group_name: str = None,
end_callback: EndCB = None, cancel_callback: CancelCB = None) -> str: