[issue33546] asyncio.Condition should become awaitable in 3.9

[Łukasz Langa]

Łukasz Langa  added the comment:

Andrew is right because a Condition *is* a lock.  The confusing thing about 
this construct is that the actual logic "condition" that we're waiting for is 
external.


It can be controlled by another coroutine that will just let us know by calling 
`cond.notify()` when the condition is met.  On the receiver side it looks like 
this:

async with cond:   # in this block you hold the lock
await cond.wait()  # (this temporarily releases the lock as long as it 
waits)
print("Another coroutine called .notify().  I hold the lock now!")


It can also be used like Andrew demonstrated above, where *we* run the logic 
"condition" check ourselves and that check *also* requires a lock to be correct:

async with cond:  # in this block you hold the 
lock
while not condition_check_with_lock():# <- this is the actual 
"condition" check
await cond.wait() # (temporarily releases the 
lock while it waits)
print("Check passed and I'm holding the lock now!")


Personally I find the latter example confusing because it doesn't require 
another coroutine to ever `.notify()` us if the initial 
`condition_check_with_lock()` returned True, but it *does* require another 
coroutine to `.notify()` us if that initial check returned False.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue33546] asyncio.Condition should become awaitable in 3.9

[Andrew Svetlov]

Andrew Svetlov  added the comment:

No, condition variables don't work this way.
The proper code looks like:

async with cond:
while not :
await cond.wait()


It cannot be collapsed to just `await cond`.

--
resolution:  -> rejected
stage:  -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue33546] asyncio.Condition should become awaitable in 3.9

[Jason Fried]

New submission from Jason Fried :

In 3.9 we can remove the deprecated pattern for accepting __enter__ and 
__exit__ for locks.  This will free up __await__ for Condition to use for 
replacing .wait() which is wart from before awaitables. 

My new proposed behavior is

await cond 

which would be equivalent of:

async with cond:
await cond.wait()

--
components: asyncio
messages: 316848
nosy: asvetlov, fried, lukasz.langa, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.Condition should become awaitable in 3.9

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com