ProxyPatternPool

Generic Proxy and Pool classes for Python.

This module provides two classes:

• Proxy implements the proxy pattern, i.e. all calls to methods on the proxy are forwarded to an internally wrapped object. This allows to solve the classic chicken-and-egg importation and initialization possibly circular-dependency issue with Python modules:

# File "database.py"
db = Proxy()

def init_app(config):
    db.set_obj(initialization from config)

# File "app.py"
import database
from database import db  # db is a proxy to nothing
…
# delayed initialization
database.init_app(config)

# db is now a proxy to the initialized object

When an internal pool is used, method _ret_obj must be called to return the object to the pool when done with it.

• Pool implements a full-featured thread-safe pool of things which can be used to store expensive-to-create objects such as database connections, to be shared between threads for instance. The above proxy object creates a pool automatically depending on its parameters.

This generic pool class can be used independently of the Proxy class.

It provides numerous hooks to provide callbacks for creation, deletion, stats, tracing, health check… which makes it ideal to manage any kind of expensive resources within a process.

import ProxyPatternPool as ppp

# start a pool with 2 resources created by "fun"
pool = ppp.Pool(
    fun = lambda n: f"expensive object {n}",
    min_size=2, max_size=2, timeout=0.5,
)

# get resources
a = pool.get(); b = pool.get()  # max_size reached
try:
    c = pool.get()  # will timeout after 0.5 seconds
    assert False
except ppp.TimeOut:
    pass

pool.ret(a); pool.ret(b);  # return resources

pool.shutdown()
del pool

License

This code is Public Domain.

All software has bug, this is software, hence… Beware that you may lose your hairs or your friends because of it. If you like it, feel free to send a postcard to the author.

Versions

Sources, documentation and issues are hosted on GitHub. Install package from PyPI. See version details.