Show HN: Async UI: A Rust UI Library Where Everything is a Future

Post by gpderetta » Thu, Oct 06, 2022, 1:11 PM UTC

naasking wrote: post #90

gpderetta wrote: post #89

Earlier quoted context omitted.

So, you didn't give the explanation of what your snippet is supposed to do but, assuming that await returns control to f (as that the only thing that can happen with stackless coroutines) the equivalent in go would be to spawn a goroutine when calling g (pseudocode as I know approximately zero go): fn f() { var v1 = ..., var v2 = ...; go g(v2); } fn g(v2) { /* do something with v2 */ } There is no await as they are i…

> So, you didn't give the explanation of what your snippet is supposed to do but, assuming that await returns control to f No, await is a context switch of some kind. In a stackful implementation the stack is switched to another thread at that point (say for an I/O wait), in an async implementation, the point after await is resumed with the live variables needed for the remainder of the program because it will be pas…

Post by gpderetta » Thu, Oct 06, 2022, 3:39 PM UTC

naasking wrote: post #92

gpderetta wrote: post #91

Earlier quoted context omitted.

So, don't you agree that the stackful equivalent of your stackless example will use something like 'go g(v1)' which will only capture v1? Without explicitly forking v2 will be captured, but then it is a completely different program with different semantics and it doesn't make sense to say that it captures more. Edit to be more practical: in c++ you can have both stackless and stackful coroutines. If you write the sam…

> So, don't you agree that the stackful equivalent of your stackless example will use something like 'go g(v1)' which will only capture v1? It will only capture v1 and also reserve a larger stack space in case the new computation needs it, where the stackless equivalent does not require this. > Without explicitly forking v2 will be captured, but then it is a completely different program with different semantics and i…

Post by bheadmaster » Thu, Oct 06, 2022, 4:39 PM UTC

naasking wrote: post #73

bheadmaster wrote: post #69

Earlier quoted context omitted.

What state does a userspace thread have to capture in order to work that a coroutine doesn't?

A userspace thread captures full a stack context, a delimited continuation used in async programming captures only the referenced variables needed for the remaining computation. This is a strict subset of the userspace thread state. For instance: fn f() { var v1 = ..., var v2 = ...; g(v2); } fn g(v2) { await; /* do something with v2 */ } // await is a context switch A userspace thread captures v1 and v2, an async com…