Good video, interesting how multi track train networks and signals are a convenient analogy for code parallelization and concurrency

Hooray! More really informative content, stuff that makes sense and is actually useful!

Interesting programming information and a train game. I'm going to subscribe to follow along with. :)

Nice technical video! Always a pleasure learning about how you overcome challenges

Pretty cool content!

I do have a question: Have you tried batching modifications of shared state? Especially cases like spawning puffs of smoke and noises seem like they should be trivially changeable to storing them in a local list in the thread first, then locking the global list if any were created and just shoving either the list object or each element of the local list into it. It may be benefitial because it means you only need to lock/atomically insert at most once per worker, or totally worse because of the extra code and copies, so I'd love to hear if you have benchmarked this!

@josiahmanson

21 күн бұрын

Good question. I think I mentioned in the video, but the sounds actually are already batched per train over several simulation ticks and are consumed by the main thread during the render update. So, sounds have no locks during the simulation. For smoke puffs I could have done the same thing, but it doesn't cost much performance as it is since the puffs aren't generated all that often (like maybe 1 in 10 frames and only if a train is moving). So, it barely shows up in profiling, a quick test just now showed 0.143 s out of a total 18.344 s run time was spent acquiring the smoke lock. But you are right, that I could probably avoid that overhead. Thanks for the suggestion. Maybe I will implement that.

@josiahmanson

20 күн бұрын

I gave smoke puffs the same treatment as sounds. I store them only in the train now, and there is no reason to have a global array to collect the smoke in, because the renderer can directly use the train arrays. I also removed the per-tick stage of the simulation where I remove smoke, because this only needs to happen once per rendered frame. At the fastest rate that is once per 1000 ticks, which also reduces overhead some. I also made my benchmarking code (that doesn't render) match that to remove finished smoke every 1000 ticks. Rough timings of the best run over like 5: 17.68 before 17.13 after train smoke optimization There is a variance of up to a second between timings, so it is hard to know precisely how much it helped, but it is clearly somewhat better by on the order of half a second. I could in theory do similar for the cargo loaders, but since those affect the sim I will still need to touch them once per tick so the benefits won't be as large. I might try that next.

@Kanonenwind

20 күн бұрын

Nice to hear back the results! Yeah, I didn't expect a big benefit out of the smoke spawning because it didn't seem like something that would happen too often, so I'm pretty amazed if it really is half a second in the end. I mainly mentioned it because this is a common technique in entity component systems to allow multithreaded systems to spawn new entities. You could probably use it in other steps of your simulation, but once one needs more than "many threads create values for one accumulation without order" you may need to add a serial fixup step or something like that, so the smoke seemed like low hanging fruit! And on the audio, you may have mentioned it, I mainly listened to the video over two days when I ate or was on break so I don't remember all the details 😅.

@josiahmanson

20 күн бұрын

​@@Kanonenwind Ya, I wouldn't expect you to remember every detail. I think the main benefit from the smoke change was not about the locking, but about my being able to skip the step in most sim ticks and do a big batch update every 1000 ticks. Most ticks there is no change in state for the smoke puffs, so repeatedly processing them was wasteful. Also there is no harm in letting smoke remain in the array past its expiration so skipping the tick it should be removed is safe. These things aren't true for cargo loaders, so I don't expect anywhere near the same benefit.

3:10 The logo has a typo "Steam Revloution" lol

@josiahmanson

16 күн бұрын

lol. oops. thanks for catching that!

@delphicdescant

14 күн бұрын

Typos increase engagement!

Ireland!!!!!

What game is this ?

@josiahmanson

23 күн бұрын

It is a game I am working on as my hobby, called Steam Revolution.

@lynnwilliam

23 күн бұрын

@@josiahmanson I love how you have a deep understanding a parallel processing and parallel programming and simulation. I have the same it is so hard to teach in a YT video. but you did a great job. Where can.I download your software?

@josiahmanson

23 күн бұрын

@@lynnwilliam Thanks for the compliment and your interest. The game hasn't been released, so isn't available for download yet.

@lynnwilliam

23 күн бұрын

@@josiahmanson can you setup maybe a reddit subreddit and link that in all the YT videos about this? Would love to hear what other programmers think. What you are doing is amazing by the way,

@josiahmanson

23 күн бұрын

@@lynnwilliam That is a good suggestion. I'll have to consider it.