asyncio-loop-local storage, singletons and deferred __aexit__'s. Init that pool once and reuse it!
Project description
asyncio-loop-local
asyncio-loop-local storage, singletons and deferred aexit's. Init that pool once and reuse it!
why have loop-local things
Suppose you have some async context manager, like aiohttp.ClientSession
:
async with aiohttp.ClientSession() as session:
async with session.get('http://httpbin.org/get') as resp:
print(await resp.text())
But the docs tell you: "don't create a session per request". So, you need to reuse it somehow, and this means you need to init it somewhere and then either pass it around all the code that might need it, or... use global variables? There must be a better way.
sticky_singleton_acm
The all-in-one solution to this is:
_ClientSession = asyncio_loop_local.sticky_singleton_acm(ClientSession)
...
async _ClientSession() as session:
async with session.get('http://httpbin.org/get') as resp:
print(await resp.text())
The wrapper gives you
- the same
ClientSession
for every combination of parameters passed to it (singleton) - that doesn't
__aexit__
when the block is over, only when the async event loop is closed (sticky ACM)
enter_once
+ singleton
Those willing to save up a level of indentation
(after all, de-denting is a no-op as __aexit__
'ing effect is deferred anyway)
might be interested in
combining two simpler primitives to the same effect:
_ClientSession = asyncio_loop_local.singleton(ClientSession)
...
session = await asyncio_loop_local.enter_once(_ClientSession())
async with session.get('http://httpbin.org/get') as resp:
print(await resp.text())
singleton
Decorate your callable that generates something, and the returned value will be cached per async loop (and per passed parameters).
_ClientSession = asyncio_loop_local.singleton(ClientSession)
_ClientSession() is _ClientSession() # as long you're in the same event loop
enter_once
Invoke __anter__
of an asynchronous context manager now,
defer __aexit__
to the end of the event loop.
Repeated attempts to enter_once
on the same object will do nothing.
session = await asyncio_loop_local.enter_once(ClientSession())
...
# __aexit__ will be executed at the end of the event loop
sticky_acm
Wrap an asynchronous context manager.
__anter__
just proxies the original context manager's __aenter__
,
__aexit__
does nothing and is deferred to end of the event loop.
It's like enter_once
, but in a form to use with async with
.
cs = asyncio_loop_local.sticky_acm(ClientSession())
async with cs: # __aenter__'s
...
# __aexit__ will be executed at the end of the event loop
enter
Invoke __anter__
of an asynchronous context manager now,
defer __aexit__
to the end of the event loop.
session = await asyncio_loop_local.enter_once(ClientSession())
...
# __aexit__ will be executed at the end of the event loop
storage
Async-loop-local storage. Like thread-local, but loop-local. All the hacks above are built up on it.
alls = asyncio_loop_local._storage.storage() # gives a loop-associated dict
alls['purpose'] = ('whatever', {'you': 'want'})
If you wanna use locking, consider this:
class LockingDict(asyncio.Lock, dict): pass
alls['careful'] = LockingDict()
with alls['careful'] as d:
d['a'] = 'b'
_atexit
There's also an async-loop-local atexit hook implementation. It's private so far until some interest is expressed.
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