vibe.d-lite v0.1.0 powered by photon

[Dmitry Olshansky]

On Friday, 19 September 2025 at 13:22:48 UTC, Sönke Ludwig wrote:
> Am 19.09.25 um 12:33 schrieb Dmitry Olshansky:
>>>> 2. There is no Interruptible* mutexes, condvars or anything 
>>>> photon doesn't support the notion and code that relies on 
>>>> interrupt needs to be rethought (including some part of 
>>>> vibe.d itself).
>>>
>>> Is this a fundamental limitation, or could it be implemented 
>>> in the future?
>> 
>> The limitation is this - photon operates inside of syscall 
>> wrappers, those are nothrow so if we get interrupted there is 
>> no way to throw anything. Plus this could be deep in some C 
>> library, not sure how exception would propagate but likely 
>> missing cleanup in the C side.
>
> Shouldn't it still be possible to set an "interrupted" flag 
> somewhere and let only the vibe-core-lite APIs throw? Low level 
> C functions should of course stay unaffected.

Since vibe-core-light depends on syscalls this would mean 
creating a separate set of API for vibe-core-light which is not 
something I’d like to do.

>>> I know interruption/cancellation is generally problematic to 
>>> get to work across platforms, but interruptible sleep() could 
>>> at least be implemented by waiting on an an event with 
>>> timeout, and I guess sleep() is the most important candidate 
>>> to start with.
>> 
>> Sleep is trivial but also kind of pointless, if you want to 
>> interrupt why not wait on the event and trigger that?
>
> It's more of a timeout pattern that I've seen multiple times, 
> there are certainly multiple (better) alternatives, but if 
> compatibility with existing code is the goal then this would 
> still be important.

I guess, again most likely I’d need to create API specifically 
for vibe. Also that would mean interrupt becomes part of photon 
but only works when certain APIs are used. This is bad.
>> 
>>>> 5. Fibers are scheduled roughly to the least loaded cores so 
>>>> all of LocalThis LocalThat are in fact SharedThis and 
>>>> SharedThat, simplifying the whole thing and making it easier 
>>>> to scale.
>>>
>>> This is okay for `runWorkerTask`, but would be a fundamental 
>>> deviation from vibe-core's threading model. Having the basic 
>>> `runTask` schedule fibers on the calling thread is absolutely 
>>> critical if there is to be any kind of meaningful 
>>> compatibility with "non-lite" code.
>> 
>> I on the other hand imagine that it’s not. In year 2025 not 
>> utilizing all of available cores is shameful. The fact that I 
>> had to dig around to find how vibe.d is supposed to run on 
>> multiple cores is telling.
>
> Telling in what way?

That running single threaded is the intended model.

> It's really quite simple, you can use plain D threads as 
> normal, or you can use task pools, either explicitly, or 
> through the default worker task pool using `runWorkerTask` or 
> `runWorkerTaskDist`. (Then there are also higher level 
> concepts, such as async, performInWorker or 
> parallel(Unordered)Map)

This does little to the most important case - handling requests 
in parallel. Yeah there are pool and such for cases where going 
parallel inside of a single request makes sense.

> Not everything is CPU bound and using threads "just because" 
> doesn't make sense either. This is especially true, because of 
> low level race conditions that require special care. D's 
> shared/immutable helps with that, but that also means that your 
> whole application suddenly needs to use shared/immutable when 
> passing data between tasks.

I’m dying to know which application not being cpu bound still 
needs to pass data between tasks that are all running on a single 
thread.

>>> In general, considering that TLS is the default in D, and 
>>> also considering that many libraries are either not 
>>> thread-safe, or explicitly thread-local, I think it's also 
>>> the right default to schedule thread-local and only schedule 
>>> across multiple threads in situations where CPU load is the 
>>> guiding factor. But being able to get rid of low-level 
>>> synchronization can also be a big performance win.
>> 
>> Most TLS using libs would work just fine as long as they are 
>> not pretending to be “globals” and the whole program to be 
>> single threaded. Say TLS random has thread-local state but 
>> there is no problem with multiple fibers sharing this state 
>> nor any problem that  fibers in different threads do not “see” 
>> each other changes to this state.
>
> But TLS variables are always "globals" in the sense that they 
> outlive the scope that accesses them. A modification in one 
> thread would obviously not be visible in another thread, 
> meaning that you may or may not have a semantic connection when 
> you access such a library sequentially from multiple tasks.
>
> And then there are said libraries that are not thread-safe at 
> all, or are bound to the thread where you initialize them. Or 
> handles returned from a library may be bound to the thread that 
> created them. Dealing with all of this just becomes needlessly 
> complicated and error-prone, especially if CPU cycles are not a 
> concern.

TLS is fine for using not thread safe library - just make sure 
you initialize it for all threads. I do not switch or otherwise 
play dirty tricks with TLS.

> By robbing the user the control over where a task spawns, you 
> are also forcing synchronization everywhere, which can quickly 
> become more expensive than any benefits you would gain from 
> using multiple threads.

Either of default kind of rob user of control of where the task 
spawns. Which is sensible a user shouldn’t really care.

> Finally, in the case of web applications, in my opinion the 
> better approach for using multiple CPU cores is *usually* by 
> running multiple *processes* in parallel, as opposed to 
> multiple threads within a single process. Of course, every 
> application is different and there is no one-size-fits-all 
> approach.

There we differ, not only load balancing is simpler within a 
single application but also processes are more expansive. Current 
D GC situation kind of sucks on multithreaded workloads but that 
is the only reason to go multiprocess IMHO.