86 lines
3.1 KiB
Python
86 lines
3.1 KiB
Python
"""
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AtomicSQL - Race-condition and Threading safe SQL Database Interface.
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"""
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import os
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import sqlite3
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import time
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from threading import Lock
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class AtomicSQL:
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"""
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Race-condition and Threading safe SQL Database Interface.
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"""
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def __init__(self):
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self.master_lock = Lock() # prevents race condition
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self.db = {} # used to hold the database connections and commit changes and such
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self.cursor = {} # used to execute queries and receive results
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self.session_lock = {} # like master_lock, but per-session
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def load(self, connection):
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"""
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Store SQL Connection object and return a reference ticket.
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:param connection: SQLite3 or pymysql Connection object.
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:returns: Session ID in which the database connection is referenced with.
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"""
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self.master_lock.acquire()
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try:
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# obtain a unique cryptographically random session_id
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session_id = None
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while not session_id or session_id in self.db:
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session_id = os.urandom(16)
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self.db[session_id] = connection
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self.cursor[session_id] = self.db[session_id].cursor()
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self.session_lock[session_id] = Lock()
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return session_id
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finally:
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self.master_lock.release()
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def safe_execute(self, session_id, action):
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"""
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Execute code on the Database Connection in a race-condition safe way.
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:param session_id: Database Connection's Session ID.
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:param action: Function or lambda in which to execute, it's provided `db` and `cursor` arguments.
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:returns: Whatever `action` returns.
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"""
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if session_id not in self.db:
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raise ValueError(f"Session ID {session_id!r} is invalid.")
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self.master_lock.acquire()
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self.session_lock[session_id].acquire()
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try:
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failures = 0
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while True:
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try:
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action(
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db=self.db[session_id],
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cursor=self.cursor[session_id]
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)
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break
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except sqlite3.OperationalError:
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failures += 1
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delay = 3 * failures
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print(f"AtomicSQL.safe_execute failed, retrying in {delay} seconds...")
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time.sleep(delay)
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if failures == 10:
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raise ValueError("AtomicSQL.safe_execute failed too many time's. Aborting.")
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return self.cursor[session_id]
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finally:
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self.session_lock[session_id].release()
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self.master_lock.release()
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def commit(self, session_id):
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"""
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Commit changes to the Database Connection immediately.
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This isn't necessary to be run every time you make changes, just ensure it's run
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at least before termination.
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:param session_id: Database Connection's Session ID.
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:returns: True if it committed.
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"""
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self.safe_execute(
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session_id,
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lambda db, cursor: db.commit()
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)
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return True # todo ; actually check if db.commit worked
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