README.md

This small snippet can be implemented in your Django project to handle locks. It is particularly useful for replacing Redis locks, reducing dependency overhead. To use this snippet, simply copy and adapted to your Django project.

The hash_string function is used to convert a string value into a numerical hash value, as PostgreSQL advisory lock mechanism requires an integer.

Tested on Python3.11 and Django4

Learn more about advisory locks in:

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

postgres_advisory_lock.py

import hashlib
from contextlib import contextmanager
from django.db import connection


def hash_string(value: str) -> int:
    hash_object = hashlib.sha256(value.encode())
    lock_id = int(hash_object.hexdigest()[:16], 16)
    return lock_id


@contextmanager
def advisory_lock(namespace_id: int, lock_name: str) -> None:
    lock_id = hash_string(lock_name)

    try:
        with connection.cursor() as cursor:
            cursor.execute("SELECT pg_advisory_lock(%s, %s);", [namespace_id, lock_id])

        yield
    finally:
        with connection.cursor() as cursor:
            cursor.execute("SELECT pg_advisory_unlock(%s, %s);", [namespace_id, lock_id])
        
company = 1
lock_name = "sales_code"

with advisory_lock(company, lock_name):
    ...