apsw_connection_pooling.py

# MIT License
# 
# Copyright (c) 2023 Michael Hall
# 
# 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
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# 
# 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
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

from __future__ import annotations

import asyncio
import apsw
from collections import deque
from typing import Any


from contextlib import asynccontextmanager


__all__ = ["ConnectionPool"]


class ConnectionPool:
    """
    It's a misuse of this class to continue using a connection
    outside of the provided async context manager.
    I may actually do the required wrapping to check for this at some point, 
    but I'm just wrapping some really simple
    behavior here and don't want to.

    with the exception of poolsize, the arguments this accepts are
    just passed through to the underlying aspw.connection(s)

    use of wal mode (see apsw.connection_hooks) is highly reccomended, but not done for you

    Lazy async use requires functions which accept a cconnection + things to pass through

        def set_user_phone_number(conn, user_id, phone):
            with conn:
                cursor = conn.cursor()
                cursor.execute(
                    '''
                    INSERT INTO USERS (user_id, phone) VALUES (?, ?)
                    ON CONFLICT (user_id) DO UPDATE SET phone=excluded.phone
                    ''',
                    (phone,)
                )
    
    elsewhere....

        async with pool.get_connection() as conn:
            await asyncio.to_thread(set_user_phone_number, conn, phone_number)

    """

    def __init__(
        self,
        poolsize: int,
        filename: str,
        # I am going to assume someone knows enough to know you can't pool sqlite connections and exclusive mode
        flags: int = apsw.SQLITE_OPEN_READWRITE | apsw.SQLITE_OPEN_CREATE,
        vfs: Any | None = None,
        statementcachesize: int = 100
    ):
        if poolsize < 1:
            raise ValueError("Must have a poolsize of at least 2")
        self._sem = asyncio.Semaphore(value=poolsize)
        self._connections: deque[apsw.Connection] = deque(maxlen=poolsize)
        for _ in range(poolsize):
            self._connections.append(apsw.Connection(filename, flags, vfs, statementcachesize))

    # not implementing close, apsw connections are self-closing at collection

    @asynccontextmanager
    async def get_connection(self):
        # There's not much point in a sync version of this IMO
        # Additionally, the connections are threadsafe, you can toss them into asyncio.to_thread if you need
        # I don't see much a point in wrapping beyond that either.

        async with self._sem:
            try:
                conn = self._connections.pop()
                yield conn
            finally:
                self._connections.appendleft(conn)  # could add misuse wrapping here by wrapping the returned connection, but... meh