SQLAlchemy-DLock

Distributed lock based on Database and SQLAlchemy.

It currently supports below locks:

• MySQL - named lock: https://dev.mysql.com/doc/refman/8.0/en/locking-functions.html

• PostgreSQL - advisory lock: https://www.postgresql.org/docs/current/explicit-locking.html#ADVISORY-LOCKS

❗ Note:

The project is not stable enough and DO NOT use it in production.

Usages

• Work with SQLAlchemy’s Connection object:

  from sqlalchemy import create_engine
  from sqlalchemy_dlock import create_sadlock
  
  key = 'user/001'
  
  engine = create_engine('postgresql://scott:tiger@localhost/')
  conn = engine.connect()
  
  # Create the D-Lock on the connection
  lock = create_sadlock(conn, key)
  
  # it's not lock when constructed
  assert not lock.acquired
  
  # lock
  lock.acquire()
  assert lock.acquired
  
  # un-lock
  lock.release()
  assert not lock.acquired
  

• Used in with statement

  from contextlib import closing
  
  from sqlalchemy import create_engine
  from sqlalchemy_dlock import create_sadlock
  
  key = 'user/001'
  
  engine = create_engine('postgresql://scott:tiger@localhost/')
  with engine.connect() as conn:
  
      # Create the D-Lock on the connection
      with create_sadlock(conn, key) as lock:
          # It's locked
          assert lock.acquired
  
      # Auto un-locked
      assert not lock.acquired
  
      # If do not want to be locked in `with`, a `closing` wrapper may help
      with closing(create_sadlock(conn, key)) as lock2:
          # It's NOT locked here
          assert not lock2.acquired
          # lock it now:
          lock2.acquire()
          assert lock2.acquired
  
      # Auto un-locked
      assert not lock2.acquired
  

• Work with SQLAlchemy’s ORM session:

  ❗ Note:

  According to https://docs.sqlalchemy.org/14/orm/extensions/asyncio.html:

  • The asyncio extension as of SQLAlchemy 1.4.3 can now be considered to be beta level software.

  • The asyncio extension requires at least Python version 3.6

  from sqlalchemy import create_engine
  from sqlalchemy.orm import sessionmaker
  from sqlalchemy_dlock import create_sadlock
  
  key = 'user/001'
  
  engine = create_engine('postgresql://scott:tiger@localhost/')
  Session = sessionmaker(bind=engine)
  
  with Session() as session:
    with create_sadlock(session, key) as lock:
        assert lock.acquired
    assert not lock.acquired
  

• Work asynchronously

  from sqlalchemy.ext.asyncio import create_async_engine
  from sqlalchemy_dlock.asyncio import create_async_sadlock
  
  key = 'user/001'
  
  engine = create_async_engine('postgresql+asyncpg://scott:tiger@localhost/')
  
  async with engine.begin() as conn:
      async with create_async_sadlock(conn, key) as lock:
          assert lock.locked
          await lock.release()
          assert not lock.locked
          await lock.acquire()
      assert not lock.locked
  

Tests

Set environment variables TEST_URLS and TEST_ASYNC_URLS for sync and async database connection url. Multiple connections separated by space.

Set environment variables NO_ASYNCIO to 1 disable asyncio tests.

The test cases load environment variables in tests/.env.

eg (and also the defaults):

TEST_URLS=mysql://test:test@localhost/test postgresql://postgres:test@localhost/
TEST_ASYNC_URLS=mysql+aiomysql://test:test@localhost/test postgresql+asyncpg://postgres:test@localhost/