We use async code in two modes which have different very different consequences for concurrency issues.
We have an imperative code flow where we perform a series of tasks that involve IO, and apply the effects sequentially. Here the biggest problem is holding a lock for a long transaction and starving the rest of the system. So we break it up into a finite state machine where the lock is held mostly during the synchronous parts.
The other is asking a lot of questions and then making a decision based on the sum of the answers. These actually happen in parallel, and we often have to relax the effective isolation levels to make this work. But it always seems to work better if the parallel task can be treated as a pure function. Purity removes side effects, which removes the need for write locks, which if applied consistently removes the Dining Philosopher’s problem. “Applied consistently” is the hard part. Because it requires not just personal discipline but team and organizational discipline.
> There is usually not much of a point in writing a finalizer that touches only the object being finalized, since such object updates wouldn’t normally be observable. Thus useful finalizers must touch global shared state.
That seems like an “Abandon hope, all ye who enter here.”
Unless I'm missing something, this has nothing to do with asynchronous code. The delete is just synchronous code running, same as if we called a function/closure right there.
This is just about syntax sugar hiding function calls.
I'm assuming you're referring to the Python finaliser example? If so, there's no syntax sugar hiding function calls to finalisers: you can verify that by running the code on PyPy, where the point at which the finaliser is called is different. Indeed, for this short-running program, the most likely outcome is that PyPy won't call the finaliser before the program completes!
We use async code in two modes which have different very different consequences for concurrency issues.
We have an imperative code flow where we perform a series of tasks that involve IO, and apply the effects sequentially. Here the biggest problem is holding a lock for a long transaction and starving the rest of the system. So we break it up into a finite state machine where the lock is held mostly during the synchronous parts.
The other is asking a lot of questions and then making a decision based on the sum of the answers. These actually happen in parallel, and we often have to relax the effective isolation levels to make this work. But it always seems to work better if the parallel task can be treated as a pure function. Purity removes side effects, which removes the need for write locks, which if applied consistently removes the Dining Philosopher’s problem. “Applied consistently” is the hard part. Because it requires not just personal discipline but team and organizational discipline.
> There is usually not much of a point in writing a finalizer that touches only the object being finalized, since such object updates wouldn’t normally be observable. Thus useful finalizers must touch global shared state.
That seems like an “Abandon hope, all ye who enter here.”
Unless I'm missing something, this has nothing to do with asynchronous code. The delete is just synchronous code running, same as if we called a function/closure right there.
This is just about syntax sugar hiding function calls.
I'm assuming you're referring to the Python finaliser example? If so, there's no syntax sugar hiding function calls to finalisers: you can verify that by running the code on PyPy, where the point at which the finaliser is called is different. Indeed, for this short-running program, the most likely outcome is that PyPy won't call the finaliser before the program completes!
I think it says if your async code holds locks you’re gonna have a bad time. Async and optimistic locks probably should go hand in hand.
I would think finalizers and async code magnify problems that are already there.
Dupe of [0], though there's only 1 comment on that submission as of this comment.
[0]: https://news.ycombinator.com/item?id=45898923