Don't suggest inside lock

[Jesse-Hufstetler]

You can't do async in a lock

Stop squigglin' me!

[avonwyss]

The reason why it isn't allowed is explained well here:
https://stackoverflow.com/questions/7612602/why-cant-i-use-the-await-operator-within-the-body-of-a-lock-statement/7612714#7612714
In summary, since locks are inherently thread-bound but async code is not, awaiting in a lock is a receipe for deadlocking.

However, by using other locking mechanisms such as SemaphoreSlim it is possible to implement rougly equivalent functionality from the locking point of view while keeping things async.

Therefore, the AsyncConverter could maybe provide a way to convert lock(X) (where X must be a object field/property only used for locking) to have X be a SemaphoreSlim(1, 1) instance and replace all usages of the lock(X) {...} with something like this:

await X.WaitAsync();
try {
  ...
} finally {
  X.Release();
}

(Note: non-async code doing lock(X) would need to do X.Wait() instead of await X.WaitAsync();)