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Adding a disk read won't break my software, but it can certainly make my software non-portable. If it suddenly expects a disk write and I'm running on a ROM, I'

Adding a disk read won't break my software, but it can certainly make my software non-portable. If it suddenly expects a disk write and I'm running on a ROM, I'm going to have a hard time. If it suddenly tries to contact google.com and I'm on an airgapped machine, I'm going to have a hard time. It's not even a matter of breaking the app actually, it's a matter of warning that "I'm going to go outside the realm of just your CPU and your memory". Sure, you could also mark as as async a function that adds two numbers. It's stupid, it's a JS thing to do, but you could. Except that you need to actively opt-in to being async in this case, as opposed to have it be forced upon you because you used a function that is also async. Blocking has meaning in a lot more contexts, and being a consultant on JVM related topics, you should know that: it's the entire purpose of Project Loom, and Loom doesn't entirely get rid of colour coding either explicitly for that purpose. Loom wasn't made because the guys at Oracle have a deep love for JavaFX, but rather takes into account the server world, where you really want to know that you're going into another context, another computer, etc. The only time where the existence of async doesn't make sense is if your entire language and ecosystem expects everything to already be distributed. In which case, you've just switched the default color to async. Finally, you chose to read async as the current JS/C# abomination implementation, but most of the sensible languages have implemented it as an effect: Kotlin has suspend funs, they don't return a Promise, but they tell you two things: they're going to touch something like the disk or the network, and if you really want to have them in a non-suspend context, you can either get a Deferred<T> out of them (and find another thread to run it on, and handle synchronization yourself), or run them on the current thread (and block everything).

mike_hearn 3y ago
Blocking in Loom is primarily about waiting for network traffic, possibly with extensions to file IO in future - it doesn't suspend if you do file IO today. Loom does get rid of coloring, or rather, doesn't introduce more of it and lets you phase out what exists, so I'm not sure what exactly you mean by that. Kotlin suspend funs do not tell you they're about to touch network disk, that's the reason they use "suspend" and not "async". Suspend funs can also use generators (with yield) in which case no I/O is happening but they are nonetheless suspending. So this is why blocking as a concept isn't a great one, IMO. The Kotlin designers were right to not use the word in their implementation of coroutines. Where Loom discusses blocking a bit, it's not defined as being about blocking, it's about being able to scale up threads to way beyond what was previously possible. It just so happens that the primary reason you'd want to do that is if you have lots of threads that spend lots of time waiting for things, but that doesn't automatically require network or disk access. For example you can use threads that spend all their time in Thread.sleep if you were writing an agent simulation.
- kaba0 3y ago
  > possibly with extensions to file IO in future - it doesn't suspend if you do file IO today Wasn’t basically all of the JDK’s file APIs rewritten to io_uring-like calls to support Loom? I have thought that IO was definitely something that Loom handled.
  - mike_hearn 3y ago
    Last I heard it was on the todo list, but maybe it got done since I last looked. You can do async IO without io_uring.
coldtea 3y ago
>Adding a disk read won't break my software, but it can certainly make my software non-portable. If it suddenly expects a disk write and I'm running on a ROM, I'm going to have a hard time. If it suddenly tries to contact google.com and I'm on an airgapped machine, I'm going to have a hard time. It's not even a matter of breaking the app actually, it's a matter of warning that "I'm going to go outside the realm of just your CPU and your memory". Sure, you could also mark as as async a function that adds two numbers. It's stupid, it's a JS thing to do, but you could. You're conflating too many orthogonal things. It's not merely because of the performance of touches disk/network that async was used for those cases, it's because that waiting is not because you're held up by the language doing calculations. That isn't the case with a function like you describe. Marking functions async when they aren't yielding just to signal that they might be slow is a bizzare idea. That's not what async is and it doesn't bring any real benefit, it's just abusing the notion (and limiting the contexts where you can run those functions). You'll still be using libraries which wont follow this strange idea, and you should know their performance characteristics. Blocking code exists in all major languages, including JS. In a single thread context, having something "async" wont help you at all, if it calls anything blocking, which can be something as common as JSON.parse >If it suddenly expects a disk write and I'm running on a ROM, I'm going to have a hard time. If it suddenly tries to contact google.com and I'm on an airgapped machine, I'm going to have a hard time. All of those have nothing to do with async, and what async is created and used for. What you want is something like Haskell's IO "tainting", a (side) effects system, or something to that (no pun intended) effect.

mike_hearn 3y ago

Blocking in Loom is primarily about waiting for network traffic, possibly with extensions to file IO in future - it doesn't suspend if you do file IO today. Loom does get rid of coloring, or rather, doesn't introduce more of it and lets you phase out what exists, so I'm not sure what exactly you mean by that. Kotlin suspend funs do not tell you they're about to touch network disk, that's the reason they use "suspend" and not "async". Suspend funs can also use generators (with yield) in which case no I/O is happening but they are nonetheless suspending. So this is why blocking as a concept isn't a great one, IMO. The Kotlin designers were right to not use the word in their implementation of coroutines. Where Loom discusses blocking a bit, it's not defined as being about blocking, it's about being able to scale up threads to way beyond what was previously possible. It just so happens that the primary reason you'd want to do that is if you have lots of threads that spend lots of time waiting for things, but that doesn't automatically require network or disk access. For example you can use threads that spend all their time in Thread.sleep if you were writing an agent simulation.

kaba0 3y ago
> possibly with extensions to file IO in future - it doesn't suspend if you do file IO today Wasn’t basically all of the JDK’s file APIs rewritten to io_uring-like calls to support Loom? I have thought that IO was definitely something that Loom handled.
- mike_hearn 3y ago
  Last I heard it was on the todo list, but maybe it got done since I last looked. You can do async IO without io_uring.

coldtea 3y ago

>Adding a disk read won't break my software, but it can certainly make my software non-portable. If it suddenly expects a disk write and I'm running on a ROM, I'm going to have a hard time. If it suddenly tries to contact google.com and I'm on an airgapped machine, I'm going to have a hard time. It's not even a matter of breaking the app actually, it's a matter of warning that "I'm going to go outside the realm of just your CPU and your memory". Sure, you could also mark as as async a function that adds two numbers. It's stupid, it's a JS thing to do, but you could. You're conflating too many orthogonal things. It's not merely because of the performance of touches disk/network that async was used for those cases, it's because that waiting is not because you're held up by the language doing calculations. That isn't the case with a function like you describe. Marking functions async when they aren't yielding just to signal that they might be slow is a bizzare idea. That's not what async is and it doesn't bring any real benefit, it's just abusing the notion (and limiting the contexts where you can run those functions). You'll still be using libraries which wont follow this strange idea, and you should know their performance characteristics. Blocking code exists in all major languages, including JS. In a single thread context, having something "async" wont help you at all, if it calls anything blocking, which can be something as common as JSON.parse >If it suddenly expects a disk write and I'm running on a ROM, I'm going to have a hard time. If it suddenly tries to contact google.com and I'm on an airgapped machine, I'm going to have a hard time. All of those have nothing to do with async, and what async is created and used for. What you want is something like Haskell's IO "tainting", a (side) effects system, or something to that (no pun intended) effect.