# util/queue.py
# Copyright (C) 2005-2025 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
# mypy: allow-untyped-defs, allow-untyped-calls
"""An adaptation of Py2.3/2.4's Queue module which supports reentrant
behavior, using RLock instead of Lock for its mutex object. The
Queue object is used exclusively by the sqlalchemy.pool.QueuePool
class.
This is to support the connection pool's usage of weakref callbacks to return
connections to the underlying Queue, which can in extremely
rare cases be invoked within the ``get()`` method of the Queue itself,
producing a ``put()`` inside the ``get()`` and therefore a reentrant
condition.
"""
from __future__ import annotations
import asyncio
from collections import deque
import threading
from time import time as _time
import typing
from typing import Any
from typing import Awaitable
from typing import Deque
from typing import Generic
from typing import Optional
from typing import TypeVar
from .concurrency import await_fallback
from .concurrency import await_only
from .langhelpers import memoized_property
_T = TypeVar("_T", bound=Any)
__all__ = ["Empty", "Full", "Queue"]
class Empty(Exception):
"Exception raised by Queue.get(block=0)/get_nowait()."
pass
class Full(Exception):
"Exception raised by Queue.put(block=0)/put_nowait()."
pass
class QueueCommon(Generic[_T]):
maxsize: int
use_lifo: bool
def __init__(self, maxsize: int = 0, use_lifo: bool = False): ...
def empty(self) -> bool:
raise NotImplementedError()
def full(self) -> bool:
raise NotImplementedError()
def qsize(self) -> int:
raise NotImplementedError()
def put_nowait(self, item: _T) -> None:
raise NotImplementedError()
def put(
self, item: _T, block: bool = True, timeout: Optional[float] = None
) -> None:
raise NotImplementedError()
def get_nowait(self) -> _T:
raise NotImplementedError()
def get(self, block: bool = True, timeout: Optional[float] = None) -> _T:
raise NotImplementedError()
class Queue(QueueCommon[_T]):
queue: Deque[_T]
def __init__(self, maxsize: int = 0, use_lifo: bool = False):
"""Initialize a queue object with a given maximum size.
If `maxsize` is <= 0, the queue size is infinite.
If `use_lifo` is True, this Queue acts like a Stack (LIFO).
"""
self._init(maxsize)
# mutex must be held whenever the queue is mutating. All methods
# that acquire mutex must release it before returning. mutex
# is shared between the two conditions, so acquiring and
# releasing the conditions also acquires and releases mutex.
self.mutex = threading.RLock()
# Notify not_empty whenever an item is added to the queue; a
# thread waiting to get is notified then.
self.not_empty = threading.Condition(self.mutex)
# Notify not_full whenever an item is removed from the queue;
# a thread waiting to put is notified then.
self.not_full = threading.Condition(self.mutex)
# If this queue uses LIFO or FIFO
self.use_lifo = use_lifo
def qsize(self) -> int:
"""Return the approximate size of the queue (not reliable!)."""
with self.mutex:
return self._qsize()
def empty(self) -> bool:
"""Return True if the queue is empty, False otherwise (not
reliable!)."""
with self.mutex:
return self._empty()
def full(self) -> bool:
"""Return True if the queue is full, False otherwise (not
reliable!)."""
with self.mutex:
return self._full()
def put(
self, item: _T, block: bool = True, timeout: Optional[float] = None
) -> None:
"""Put an item into the queue.
If optional args `block` is True and `timeout` is None (the
default), block if necessary until a free slot is
available. If `timeout` is a positive number, it blocks at
most `timeout` seconds and raises the ``Full`` exception if no
free slot was available within that time. Otherwise (`block`
is false), put an item on the queue if a free slot is
immediately available, else raise the ``Full`` exception
(`timeout` is ignored in that case).
"""
with self.not_full:
if not block:
if self._full():
raise Full
elif timeout is None:
while self._full():
self.not_full.wait()
else:
if timeout < 0:
raise ValueError("'timeout' must be a positive number")
endtime = _time() + timeout
while self._full():
remaining = endtime - _time()
if remaining <= 0.0:
raise Full
self.not_full.wait(remaining)
self._put(item)
self.not_empty.notify()
def put_nowait(self, item: _T) -> None:
"""Put an item into the queue without blocking.
Only enqueue the item if a free slot is immediately available.
Otherwise raise the ``Full`` exception.
"""
return self.put(item, False)
def get(self, block: bool = True, timeout: Optional[float] = None) -> _T:
"""Remove and return an item from the queue.
If optional args `block` is True and `timeout` is None (the
default), block if necessary until an item is available. If
`timeout` is a positive number, it blocks at most `timeout`
seconds and raises the ``Empty`` exception if no item was
available within that time. Otherwise (`block` is false),
return an item if one is immediately available, else raise the
``Empty`` exception (`timeout` is ignored in that case).
"""
with self.not_empty:
if not block:
if self._empty():
raise Empty
elif timeout is None:
while self._empty():
self.not_empty.wait()
else:
if timeout < 0:
raise ValueError("'timeout' must be a positive number")
endtime = _time() + timeout
while self._empty():
remaining = endtime - _time()
if remaining <= 0.0:
raise Empty
self.not_empty.wait(remaining)
item = self._get()
self.not_full.notify()
return item
def get_nowait(self) -> _T:
"""Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the ``Empty`` exception.
"""
return self.get(False)
def _init(self, maxsize: int) -> None:
self.maxsize = maxsize
self.queue = deque()
def _qsize(self) -> int:
return len(self.queue)
def _empty(self) -> bool:
return not self.queue
def _full(self) -> bool:
return self.maxsize > 0 and len(self.queue) == self.maxsize
def _put(self, item: _T) -> None:
self.queue.append(item)
def _get(self) -> _T:
if self.use_lifo:
# LIFO
return self.queue.pop()
else:
# FIFO
return self.queue.popleft()
class AsyncAdaptedQueue(QueueCommon[_T]):
if typing.TYPE_CHECKING:
@staticmethod
def await_(coroutine: Awaitable[Any]) -> _T: ...
else:
await_ = staticmethod(await_only)
def __init__(self, maxsize: int = 0, use_lifo: bool = False):
self.use_lifo = use_lifo
self.maxsize = maxsize
def empty(self) -> bool:
return self._queue.empty()
def full(self):
return self._queue.full()
def qsize(self):
return self._queue.qsize()
@memoized_property
def _queue(self) -> asyncio.Queue[_T]:
# Delay creation of the queue until it is first used, to avoid
# binding it to a possibly wrong event loop.
# By delaying the creation of the pool we accommodate the common
# usage pattern of instantiating the engine at module level, where a
# different event loop is in present compared to when the application
# is actually run.
queue: asyncio.Queue[_T]
if self.use_lifo:
queue = asyncio.LifoQueue(maxsize=self.maxsize)
else:
queue = asyncio.Queue(maxsize=self.maxsize)
return queue
def put_nowait(self, item: _T) -> None:
try:
self._queue.put_nowait(item)
except asyncio.QueueFull as err:
raise Full() from err
def put(
self, item: _T, block: bool = True, timeout: Optional[float] = None
) -> None:
if not block:
return self.put_nowait(item)
try:
if timeout is not None:
self.await_(asyncio.wait_for(self._queue.put(item), timeout))
else:
self.await_(self._queue.put(item))
except (asyncio.QueueFull, asyncio.TimeoutError) as err:
raise Full() from err
def get_nowait(self) -> _T:
try:
return self._queue.get_nowait()
except asyncio.QueueEmpty as err:
raise Empty() from err
def get(self, block: bool = True, timeout: Optional[float] = None) -> _T:
if not block:
return self.get_nowait()
try:
if timeout is not None:
return self.await_(
asyncio.wait_for(self._queue.get(), timeout)
)
else:
return self.await_(self._queue.get())
except (asyncio.QueueEmpty, asyncio.TimeoutError) as err:
raise Empty() from err
class FallbackAsyncAdaptedQueue(AsyncAdaptedQueue[_T]):
if not typing.TYPE_CHECKING:
await_ = staticmethod(await_fallback)
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