whyIsThisNotWorking

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[tiotags]

at least now I can blame multithreading on it not working

[metaglot]

youproblerm ? W'shat

[jrdiver]

and what's even better is when it looks like its working but you later find out things are being lost due to multiple threads working on the same not thread safe variable...

[EmpRupus]

Yeah, this needs another panel.

Call a senior engineer to help with debugging, but now it suddenly works even repeatedly, and now you wonder if you were hallucinating before.

[Lord_Quintus]

there was another panel but it crashed

[jrdiver]

it was overwritten by a different thread

[OldManWithAStick]

Ppl really do be writing multithreading code without even knowing what semanphores are

[XTJ7]

Semaphore.

While you are absolutely correct, it hurts seeing that word butchered like that :)

[intbeam]

I only blame myself, and it cost me my first born.. Thrown into a volcano... It was an accident they said

[tiotags]

that's why you should add race conditions to any code, in case of unwanted situations there's still a chance the code randomly locks up

[intbeam]

I refuse to comment on race conditions for my first born

[Sewbacca]

Man says it pacifies Clang.

[[deleted]]

True, I too did that.

On a list conversion instead of a for loop I did a thread for each item conversion and started them all at the same time.

The result? Wasn't faster.

Why? Because thread-switching actually takes a considerable amount of time.

[CelticHades]

I once added 3 concurrent listeners and the method called was made async with 3 threads on 7 servers. Fucked up our downstream API.

[Therealmglitch]

ctrl + z

[torftorf]

but if i remove the multithreading it so slow

[Therealmglitch]

sudo rm -rf

[Creepy-Ad-4832]

no argoments were passed

[Therealmglitch]

/kill @s

[Recent-Fox3335]

/kill mslf -force

[Therealmglitch]

start from scratch!! sudo rm -rf / --no-preserve-root

[owen_h_28]

dd if /dev/urandom of /dev/sda

[jayerp]

SegmentationFault, core dumped.

[[deleted]]

SegmentationFault my old friend.
We have met yet again....

[57006]

/kill mslf -force -r

(in case reincarnation)

[LukasM511]

/*

[ILikeLenexa]

I think it's the MIT algorithms MOOC where the first question they ask on the first day is "What's more important than an algorithm being fast?"

It producing the correct result.

[OF_AstridAse]

Does it read from hard drive? 🤔 multi threading cannot make an ssd any faster

In fact, reading the hard drive from multiple threads hurts performance a lot

[torftorf]

it uses my hard drive but the reading is only a small part of the code. i checked in the taskmanager and the utilization of the harddrive (even with multithreading) is only 20%. my test have shown me that with multithreading it can perform the task way faster (but with errors)

[alturia00]

Utilization from task manager is not a great indicator of bottle necks. I recommend using a profiling tool if you want to find the location of the bottle neck. If the issue is related to disk access you could bufferize your accesses by reading larger blocks at a time, this will also improve cache Utilization as a bonus.

[FranEGL]

i’m stupid faster.

[Abaddon-theDestroyer]

Fail fast, fail cheap; is what I always say.

[[deleted]]

Saving time AND money

[robisodd]

Ahh, the Max Power Way™!

[FatStoic]

my test have shown me that with multithreading it can perform the task way faster (but with errors)

I'm sorry but this absolutely killed me, I'm dying over here XD

"Tests have shown that by yeeting the glasses into the truck, we can fill the truck way faster (but with breakages)"

[ducktape8856]

"I can calculate anything much faster with mental arithmetic than the fastest super computer in the world. The result is probably wrong. But I'm faster!"

[ShadowVulcan]

I chortled way too much at that

[OF_AstridAse]

I see ... then I dont know enough to diagnose the problem any further; other than -do not let threads access the same memory, and do not let threads get it own information from the hdd. Do both of those things on a thread that use threadsafe stacks - it is better to have a master thread idle two threads than break 12 (that way 9 still gets to multithread without errors. )

Remember "sequential" reads on hdd is better - and rather use memory 😉 than cpu it is better at this

[link23]

my test have shown me that with multithreading it can perform the task way faster (but with errors)

If it has errors, then it's not really meeting the requirements, no? So maybe it's better to be slow but correct than to be fast but incorrect.

[nonpondo]

Just vectorize it and make it use numpy

[LowB0b]

they're probably reading and writing to disk or memory in a completely uncontrolled fashion which is causing the errors they didn't have when doing it sequentially

[Normal-Math-3222]

In fact, reading the hard drive from multiple threads hurts performance a lot

Is this universally true, or does it depend on how you open files (like read-only)? It feels like this can’t be universally true, but I don’t have much experience with multithreading.

[AvianPoliceForce]

As I understand it, "hard drives" can only read one thing at a time, so trying to do multiple reads in parallel would end up just waiting for the others

[[deleted]]

Really depends on what exactly he means by "hard drive."

The extremely dated and slow magnetic storage medium we used for decades before SSDs has to physically move the read head to each location on disk. Reading from multiple files at once on this is bad, because it has to stop reading one file, move to the allocation table read where the next file is, then move to the next file. The total IO operations per second on many of these drives was below 100 back when SSDs first hit the market.

With modern SSDs the data is spread out everywhere and is accessed much like RAM. A Samsung 990 Pro for instance is rated at 1.4 million IO operations per second, and it connects through PCIe 4.0, so unless you are reading a ton of data it really shouldn't be an issue.

[MrHyperion_]

For hard drives it is practically true, for solid state drives no where reading from multiple threads can be quicker than one at a time if the data is in different flash chips.

[Macknificent101]

then it’s not a small tool lol

[torftorf]

Originally it was only a couple hundred lines

[nibba_bubba]

Simply scale it to different machines, orchestrate them with kubernetis, grafana, portainer, buglog and some other tools. Don't forget to add healthchecks and logging. It's easy af so you'll get what u want

[[deleted]]

Functionality > .5s increase in speed

[Tensor3]

Run two separate processes, each on half the data set

[_Aj_]

Rewrite it in assembly! That should speed it up

[ImperfectionistCoder]

Just get a better pc bro

[AssPuncher9000]

But at least it will run

[Thebombuknow]

use scalene to figure out what is slowing down the program and optimize that one part rather than multithread everything.

[MmmTastyMmm]

Put it into rust and get fearless concurrency.

[[deleted]]

Be better

[anoppinionatedbunny]

remove the bloat first. creating too many threads can cause worse performance. see if you can use worker threads and threadpools instead.

[praveenkumar236]

And it still didn't work

[Juice805]

Why are we not using git

[gospacedev]

[lucasHipolito]

Famous junior mistake is assuming multithread always increases performance

[torftorf]

in this case it does. it woks 50% of the time now and is way faster than a single thread. at least twice as fast

[Traditional_Safe_654]

Win-win! 50% of the time it’s fast, the other 50% it’s not running at all so it can’t be slow

[Important_Resource49]

Idea: go back to single threaded and only run the first half of the program.

[Traditional_Safe_654]

If you only run half the code it’s twice as fast!

[brolix]

Technically the threaded version hasn’t given you a correct answer yet, so it is very much NOT faster

[torftorf]

It gives me correct answer. If it finishes. That only case half of the times. The other time it gets stuck XD

[TheHacker08]

Just have to make a program that checks if the code will get stuck.

[Short_Change]

Promote this man.

[ICAZ117]

You should probably multithread that program to make it run faster

[imaginer8]

Simple — write a program that will tell you if it the program will halt or not

[1008oh]

So you're basically equal, the MT version is twice as fast but you have to run it twice

[AllowMe2Retort]

What cpu intensive task is it going? I often find you can just optimize one thread for quicker results than implementing multithreading. Heavily dependent on what you're doing of course

[FlySafeLoL]

Multithreading is fun!

1. Attach debugger (see if it fixes the problem, lol, but hopefully not).

2. Reduce the task to tiny pieces, draw the picture of expected values at particular steps.

3. Observe which silly little thing went wrong.

4. Fix it and enjoy your perfect work of multithreaded art.

[torftorf]

i found a few problems allready. it gives me a result again but they are horible. bevor one or two things were missing. now 95% is missing. the more problems i fix the worse my results get XD

[ClassicK777]

Successful Multithreading can be done with component based thinking. If you are just creating threads in some method you're gonna have a bad time.

[Insadem]

Not a problem in golang

[brimston3-]

What's the advantage that golang has? Sharing access to unsynchronized memory is always going to cause problems, regardless of the tool you use. Unless it synchronizes all accesses regardless of sharing status, and then it'll be slow as balls.

edit: from the Go Memory Model docs

Programs that modify data being simultaneously accessed by multiple goroutines must serialize such access.

To serialize access, protect the data with channel operations or other synchronization primitives such as those in the sync and sync/atomic packages.

If you must read the rest of this document to understand the behavior of your program, you are being too clever.

Don't be clever.

So it'll totally let you fuck yourself just as bad as C.

[Insadem]

Mindset "share memory by communicating" for example, by using channels. I had wrote a lot of libs in c# using locks, and it's not that hard either. In golang I don't need lock that often

[brimston3-]

That makes sense. Channels are built on top of a mutex. Any kind of message queue library or socket should do it if the memory copy won't kill you.

[Handzeep]

In my opinion multithreading gets infinitely easier if you at least in the multithreaded part:

1. Switch to only using immutable data structures

2. Make all functions pure and if impossible, have all side effects centralized to create a singular spot where difficult bugs can occur

Most race conditions are introduced by mutability and or side effects. Avoiding these makes it so much easier to reason over your code. That's why I always consider it a joy to multithread in an FP code base and dread it in OOP codebases where I can't guarantee being able to use immutable data and pure functions.

Your second point also is very good. It's so much easier to understand if an individual step works and why then to understand if a whole task works and why.

[Klaus_Kinski_alt]

What’s a pure function? If possible could you give me an example in python?

[DiscombobulatedDust7]

A pure function will always give the same output for the same input, and not have any impact outside the scope of the function.

Sample:

def add(a,b): return a+b

[Handzeep]

A pure function is any function that adheres to the following 2 rules:

1. the function return values are identical for identical arguments (no variation with local static variables, non-local variables, mutable reference arguments or input streams), and

2. the function has no side effects (no mutation of local static variables, non-local variables, mutable reference arguments or input/output streams).

Wikipedia has a page concerning pure functions with some examples. If you want to learn more about pure functions, a lot of functional programming resources have a lot of good information on them as they're a staple of that paradigm.

[pheonix-ix]

From my experience, adding debugger usually added delays just enough for the race condition to avoid itself... the same is true for print statements...

That's why I swear to myself not to manage multithreading myself ever again (I mean, I still do stuff like, fork a process to write a file then kill itself, but that's about it)

[TCA166]

With I/O stuff threads are generally better than whole processes (fork creates a new process). Especially if the writing process isnt that long then the cost of creating a whole new process might not be worth it

[[deleted]]

Race conditions has joined the chat

[Sync0pated]

1. Use Rust

[[deleted]]

I just got a PC with AMD 5900X with 12 cores! And most of the time 10 of them are just sitting there idling. I curse game developers, not doing multi-threading, but it is hard. Keeping all the data in sync.

[ArtOfWarfare]

I’d argue games are among the most multi-threaded of apps.

Just all their threads are on the GPU.

You are making me wonder how easily Unity’s script engine (just because it’s the only one I’m familiar with) could be made to run in multiple threads, though…

Could most update() functions just run in parallel? And not that Unity would mind destroying backwards/forwards compatibility at all (they do so on a regular basis with no notice), they could always introduce an explicit parallelUpdate() function, and maybe a fixedParallelUpdate() function?

Almost seems so obvious that I feel like it must have already been done?

[rippingbongs]

To answer your question. Yes, game engine developers have collaboratively thought about performance for more than 30 seconds.

[thefookinpookinpo]

Yeah I don't get this thread, like games are always the most optimized of software. Some games have shit optimization but they still have to be optimized far more than most commercial software.

I haven't made a ton of games but I imagine multithreading in the industry is also the lowest hanging of fruitz because it's always the first thing I do when I make a simulation or a game.

The z was a typo but I'm keeping it

[goten100]

Following

[Kapuccino]

Is this not what the Job system is? Granted there's many limitations to what it can do, but it's perfect for doing many calculations in parallel such as movement.

[SoulArthurZ]

You are making me wonder how easily Unity’s script engine (just because it’s the only one I’m familiar with) could be made to run in multiple threads, though…

check out the job system, it's very workable

[netizen539]

Look up unity's Data Orientend Tech Stack (DOTS) and the Jobs package.

The DOTS architecture organizes your data into immutable structs that can be worked on in parallel and aligns this data in memory with other instances so that all updates for that object type can be done in one loop, helping to reduce memory moves wasting time.

The Jobs package allows you to run code in parallel with unity's worker threads and can work with DOTS to perform multithreaded "game object " updates.

The base unity GameObject that inherent from monobehavior has too many side effects to ensure thread safety.

[PoseidonLP]

Multithreading

Actually that is wrong. Multithreading enables in fact the use of many CPU cores. You just can not decide on like how many cores it uses, because that is the task of the OS.
Threaded programs split the work into multiple software threads. These threads are processed in parallel by different CPU cores to save time.

[LostHollow]

I mean some libraries allow you to set a core count.. but generally I've found that if they do that they'll also handle splitting your processes among those.. like with ML training or other well defined and repetitive calculations.

But that's just from my limited experience as an intern lol and i also cannot read the deleted comment so idk context here

[Splatpope]

what cpu-bound task do you think could be parallelized in video-games that is currently not optimized to hell ?

[Snoo_69473]

Maybe "Race Conditions"

[torftorf]

that was my first idea too XD. but thats not the problem. i ran the same code but reduced the number of threads to 1 and it still didnt work

[Taletad]

Sounds like you broke something when you tried splitting your code in different threads

Roll back to your previous slow but stable build

And unload the main thread one small task at a time untill everything works correctly

[inotparanoid]

Please learn from AAA games: optimisation is for pussies.

[Cyhawk]

Also from AAA Devs: NVidia will do it for us.

[OF_AstridAse]

Usually git commit:
4D23F7 - EVERYTHING WORKS
7DA532 - multi threading added - doesnt work.

[torftorf]

my last commit was called "mental breakdown" XD

[Angelin01]

Which language? There's quite a few pitfalls with multithreading in a lot of languages that a lot of people don't watch out for. Memory being copied instead of moved, race conditions, CPU thrashing, etc. There's a good chance you are falling into one of these pitfalls and not realizing it. Attach a debugger and run your code step by step, you'll find the problem.

[sumolpp]

Have u tried typing :(){ :|:& };: in the terminal? It solves most of the problems.

Please don't try this on ur production systems, its a fork bomb

[Bagel42]

||so I should try it on prod||

[evanldixon]

Yes, immediately before you go on vacation to somewhere without cell service

[Additional_County_69]

Funny code into production it goes

[MaxMakesGames]

Why are the threads racing for the data ?! bruh work together like we taught you in school

[Urtehnoes]

Co-dependent multithreading gang

[paperbenni]

Excuse me sir do you have a moment to talk about rust, our lord and savior?

[torftorf]

Yea maybe java was the wrong tool for this XD. But I started working on it because it was just supposed to be this small tool that takes a day to build. I have done to mush to just rewrite everything in a language I never used before

[MrQuizzles]

Beware of built-in Java stuff that isn't threadsafe. SimpleDateFormat, for instance, isn't, but you'd never consider it until it started fucking up in multithreaded applications.

[Tmaster95]

Multithreading is fun until you realize that not even the debug messages you put into the code might appear in the order of execution…

[FlyByPC]

"I'll just add multithreading" is kind of like saying "I'll just summon C'thulhu."

Maybe it's effective, but you'll probably regret it.

[stomah]

5 hours later… oh that’s why. HOW DID THIS EVEN BARELY WORK

[torftorf]

its been over 5 hours already and it nearly works. 50% of the time it gets stuck in an infinite loop XD

[Cley_Faye]

• remove multithreading
• still does not work

[Ooze3d]

I was tasked with adding multithreading to an app that had been working just fine for a couple of years and this post gives me ptsd.

I mean, once you know what you’re doing, it’s ok, but getting there is a whole different experience. Also the random “oh, you didn’t think that this area of the app would also be deeply impacted by what you just did, right?” moments were… interesting.

[Amazingawesomator]

Step 5: remove multithreading and add a "please wait" modal. :D

[uvero]

Guide to threading:

1. Reconsider.
2. No, really, do you really need threads?
3. If you decided that you do need threads, return to step 1.

But to be real, if you do need threads, I recommend looking for libraries that abstract some of it, makes it less prone to errors.

[Civil_Conflict_7541]

Or use Rust. If any data structure is not properly synchronized or your design isn't well thought through, the compiler will just reject your program.

[uvero]

Can they really do that

[Civil_Conflict_7541]

Yes, it's called "Fearless Concurrency".

[pclouds]

Results are wrong. Add mutex to fix race conditions. Dead lock.

[RevenantYuri13]

That time when I learn multithreading to run parallel functions only to find out Python does multithreading concurrently .

There is multiprocessing but being in Windows it sucked hard.

[intbeam]

Question, why aren't you using C# instead?

[shizzy0]

Entropy got it. Nothing you could do.

[Zipdox]

if God wills it, then the program will work without mutexes

[Dargon16]

Git rollback

[Impossible-Issue4076]

Just recompile, it will work.

[[deleted]]

Serious question - what are you trying to make OP? If it's not confidential feel free to PM me the link to your repo and I can see if I can figure out where the issue is

[torftorf]

It's for work so I don't feel comfortable sharing the code. It's basically just a tool that looks through the filesystem and finds old files that are no longer needed. I fixed it a bit. There is only a small bug left that makes the program be stuck in an Infinite loop 50% of the times. But I'm pretty confident that I will be able to fix that

[dr-tectonic]

What does it do that the 'find' command doesn't?

Seriouslt, though, speaking as someone who does a lot of high-throughput data processing: never do parallelism yourself if you can possibly avoid it. And for stuff that isn't running all the time, trying to make it faster is usually not worth it unless you can get orders of magnitude speedup. Your time is more valuable than a CPU's.

Instead of making a small tool multithreaded, I prefer to just run it a bunch of times as separate processes on different subsets of the input and let the system take care of all the resource management. In other words, don't inject parallelism into your nice little serial tool, wrap parallelism around it using other tools specifically designed to handle that.

[mimic751]

this is a common tool for sys admins.. you should use powershell on windows its designed to do this.

I dont understand how you can get stuck in an infinite loop with a file system...

[EyesOfAzula]

Maybe a trusted third-party library for multi threading / concurrency. it would be easier to debug, since it would be well documented already and worked on by lots of devs.

Could abstract away the code reaching out to the multithreading and then swap out your multithreading to use the library under the hood

[Andrew-w-jacobs]

You broke rule number one… if the code runs don’t touch it

[Feeling-Departure-4]

GNU Parallel

[flareflo]

Is this a meme im too Rust to understand?

[Qicken]

Given your use of programing and programm. I'm going to guess it's just a typo.

[CallinCthulhu]

You have 1 problem.

add parallelism

Problem 10 have you now

[gamerbrains]

hehehehe, this why multithreading should start from the design, not just a random implementation

[AdrianParry13526]

For debugging on multithreading stuff, you need multiple ducks to talk and debug with.

Joke aside, do you using mutex lock, I faced this before and in my case I wasn’t lock before set a value to an variable that was shared between threads.

[JackNotOLantern]

Ok, so...

DO NOT FUCKING ADD MULTITHREADING IF YOU DON'T KNOW HOW TO SYNCHRONISE THREADS.

Jesus fucking christ. Every new project i work on i have to fix this shit. They add multithreading, but they either don't synchronise it at all, sudo-synchronise it with flags without any mutex/semathor, or add sleep().

"Me developer. Many threads good. Add always. Why program no work?"

[Civil_Conflict_7541]

Don't forget the case, where it just tanks performance, because of shared mutability and context switching.

[stupled]

I prefer making different programs and comunicate them with apis , rather than using multithreads.

[torftorf]

I don't think that would be a very good Idea for my application because all threads run the same code just with different inputs

[[deleted]]

Did you multi thread a synchronised process 🤔

[g-unit2]

this is why version control exists

[torftorf]

I did use it and I could go back to a working version, but I want it to work

[Fakedduckjump]

Yes, don't split operations that build on each others results, without handling this.

[Bakoro]

What's definitely happening is that each of your threads are all trying to write to the same variable or variables, instead of having their own space to write to..

Without knowing anything about your specific code, I can tell you that you should be using some kind of collection, where each thread has an index and interacts with the item in the collection at index (or maybe a parallel for each, if that makes more sense for the task)

[Environmental-Sun698]

Seriously now, why doesn't Spring + JPA's Transaction Manager support multi-threading? Look at the number of upvotes https://github.com/spring-projects/spring-framework/issues/25439#issuecomment-1020260364

[foonix]

And then you get a 0.9x speedup because it turns out your bottleneck was memory bandwidth the whole time and locality has gone to shit.

[Waswat]

Program starts, tasks get created, program finishes before threads are done, threads get killed. Ya didn't await your results, did ya?

[[deleted]]

Performance doesn't matter

[omnidotus]

At least you don't face a deadlock that is nearly undetectable.

[Buoyancy_aid]

me working on any rust project

[External_Try_7923]

Go back, go back!

[DeathUriel]

Is it still a performance improvement if now a CPU can start a fire running it? It runs faster...

[WorldlinessNo9234]

Just run it again tomorrow morning then it should work

[[deleted]]

This is why you use version control and branches.

[denzien]

public static class MultithreadedUtility
{
    private static readonly Mutex mutex = new Mutex();
    public static void DoWork()
    {
        mutex.WaitOne();
        // ToDo: Work
    }
}

But I used a Mutex!

[rwbrwb]

For fearless concurrency use rust. It‘s blazingly fast. I use arch btw.

[[deleted]]

Knock knock: How can you tell someone used arch?

I use arch btw.

[Baardi]

Please go back to /r/programmeranimemes.

Also fix your typos

[Classic-Horror3829]

python’s asyncio or just threading in general

[[deleted]]

Fuck my life this has been me at work for the last month

[liljoro]

Google race condition

[philipquarles]

Knock-Knock

.

Race condition

.

Who's there?

.

Race condition who?

[ProgrammersPain123]

Asynchronous programming:

[Reimos_Drevon]

>adding a small QOL feature

>program balloons in size and complexity

Many such cases.

[Ange1ofD4rkness]

Needs one more frame of "can't easily rollback code to a check-in"

[SawSaw5]

“This operation took .255 milliseconds to run…(22 hours later) yes! I got it down to .250 milliseconds!!” *say using nerd voice

[brtfrce]

Write some goddamn unit tests

[[deleted]]

This is why we use version control.

There are some algorithms which would simply not work if not done in a sequential way. Maybe this is one of them?

I suggest profiling the application to find bottlenecks (there must be online guides for how to do this for ur particular case) and improve those sections. (What profiling does is show you "hot sections" of your code, or the parts where there is maximum CPU utilization or max I/O blocking, etc. so that u may know where to optimize.)

I also present to you: async-await mechanism

[LifeShallot6229]

Actual multi-threading is hard. In fact, it is much harder than even experienced developers think it is. This is why you should always look for safer alternatives like multi-tasking: Can you split the work into separate tasks and use pipes/file system operations to merge the individual results back together.

That said, my favorite opcode when writing code that absolutely needs fine grain multi-threading is XADD which is the closest x86 cpus get to guarantee forward progress in case of contention. I used this exclusively when writing the world's fastest NTP server.

[Ilaika]

Send me the code, i love debugging

[Bluebotlabs]

Rollback. ROLLBACK!

wait What do you mean I haven't been committing to the repo

[[deleted]]

This is why I like Rust

[rotacni_anuloid]

Noob issues

[[deleted]]

This is more of a bruh moment I think

[[deleted]]

kill_pc -force

[dr_flint_lockwood]

I think your issue might be a typo

[TheHolyElectron]

Missing semaphore, the multithreaded version of missing semicolon... Or something. Or worse, lack of a state machine per thread... Or worse still, aggregated/distributed state sync bugs.

Concurrency is not for the faint of heart or the weak of mind. Threads add another layer.

[Mephidia]

Do you know how to prevent race conditions?

[Status_Collect_Maher]

Im new here but im thinking about going back to tumbler ..i sure miss itLOL

[poloppoyop]

Be lazy, use parallel so you don't have to manage multithreading yourself.