Threads in C++
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- čas přidán 9. 06. 2024
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Hey guys, looks like CZcams is still processing this video (#classic), so hopefully it will be in HD soon. Thanks for watching :)
Could you also make a video on mutexes and atomic variables. I am mainly confused about who should own the mutex in an OOP scenario...
PlutoYT: if you had just called the function, you wouldn't be able to wait for user input to terminate the loop. The best you could do is ask at each iteration of the loop whether to continue.
Thank your for all your effort. With your videos I'm starting to understand much more things in c++. Greetings from Poland!
Why your int main() not returning anything? Shouldn't that cause error?
in c++, if you dont write return 0; at the end of main function, it presums that ends with that.
Explaining thread in the woods because another cherno::thread is using the house for another video
such an underrated comment lmao
too funny
indeed
I will yeld on that
Pretty nice *Syntactic Sugar!*
Walked in the woods, found a
Cherno doing c++ multithreading.
Yee
DOLLAR
money
Yee underrated comment
He's no longer THE Cherno. He's pluralized.
Cherno gave us a simple and great example of how to display a looping "Loading" text animation while waiting for our models and other materials to load. We learn c ++ with practical examples. Great things for beginners. Thanks dude!
everyone's gonna be surprised they can exit their loading screen by pressing enter! genious game design!
There are plenty of good C++ tutorials out there, and this is by far the best C++ channel. Thank you.
Cheers to Cherno! Hands down the best C++ tutorials. My guy somehow manages to explain a relatively complex topic along with example in about 10 mins. Just Awesome.
I miss these videos in nature 😢
I bet there was a bear family just behind you hiding in the bushes and learning C++:D
great tutorial thanks a lot
You're doing great job bro. You are explaining things in a really clear way and not doing it in a boring way. Lucky to find you
Thanks for the C++ tutorials. I have seen most of your videos multiple times over the last few years.
Now, your videos are my reference content whenever I need something in C++
You are great at making things interesting. Loved all your videos so far. Thank you.
Thx for this series, exactly what i needed right now ! :)
Dude I LOVE that you are in the woods. I want my office as programmer and engineer to be the summit of some mountain or in the middle of the forest. Thats badass.
Immediately reminds me of Ex Machina!
I have been waiting for this for so long...
Thank you for the clear tutorial! Very easy to follow your explanations
I really like your videos. Great knowledge and charisma!
Love how you explained this. Ended up watching your video instead of my instructors' lecture because it was more content in less time more completely explained. Thanks for what you do!
A video on exception handling and a video on callbacks would be awesome if you haven't done those topics yet! Awesome videos man, you are a great teacher.
Came here because of the recommendation, stayed to see how C++ enables threading, learned that C++ offers custom literals
Brilliant production Cherno! Both informative and aesthetically pleasing. I'm really looking forward to the new game engine series.
This series is absolutely outstanding!
Unique ideas to appear cool in CZcams! It sure is working.
Every Time I have a problem just you clarifying it gets me going!
that's something I was thinking about some time ago, great think and great video
My wish is that maybe one day teach us about Neural Networks in C++. I'm loving your C++ series man !
Alex Tol, van If you want to get into neural networks, C++ doesn't have as many libraries and options compared to a highly supported language like Python.
It's difficult implementing neural networks in C++ I agree, but if it is fast and efficient plus it gives you more control.
Not too difficult I can send u some code of a simple one if u want...
Neil Tsakatsa I agree C++ has major performance benefits, but in my opinion, C++ isn't the best in terms of helping beginners.
just use (py)/torch if you want fast GPU accelerated networks, else if you are CPU bound use Caffe
That is so cool!!! like this multi-threading stuff is so freaking cool
Hey Cherno - Amazing series. I would be very interested in a couple that explore optimisation strategies in greater detail.
I was teaching myself some network programming using UDP sockets and was printing off the state of the server into the console. Problem is that std::cout is really slow and it was taking up so much time my server was lagging behind the game. So what I did was stick the std::cout into a thread of it's own and put it in an infinite loop and just sleep it for 0.2 seconds after every draw. Just a toy example but something simple that shows the usefulness of threads.
OMG i have been waiting
Love your introductions.
Note: in real applications one should always use e.g. std::atomic for s_Finished (or other ways to ensure thread safety) to avoid race condition, which is a kind of undefined behaviour, which is very bad.
Is this necessary when you are only writing to it from one thread?
This example is completely thread safe for 2 reasons:
1. Because he only modifies the value of the flag on the main thread so other threads could read its value without any problem. (2 thread cannot modify a variable value at the same time, that would cause a nice crash).
2. Boolean value is stored on a signle bit (0 = false, 1 = true), that means if the main thread changes its value at the same time the side thread read its value, it would be 0 or 1 anyway (so if its 0 the next time he checks it it gonna be 1 anyway). This is not true with real numbers where this technique can lead you to data corruption.
In engines such as UE4 and others this technique is used heavly, because you don't waste any time on setting up mutexes and checking its locks, etc...
The code from the video "kind of works" which means it definitely works on x86 in most popular current compilers (but might break due to boolean check elimination if you enable optimization ), but is not guaranteed to work on other platforms or even future compilers because it exhibits undefined behaviour according to C++ memory model. Boolean writes (and int writes) are atomic on x86, but, say, int writes are not atomic to non-aligned addresses on ARM. I believe even bool writes might be thread-unsafe on some platforms due to memory barriers (one core sees "false", another sees "true").
Now, if you only write for x86 and did check that all current processors/compilers accept it, and have commented it heavily to avoid future bugs by non-suspecting future programmers, then maybe it's OK to write such code. But I think in that case one should know that they are breaking the rules of C++ memory model: one should assess the risks/rewards for their particular situation, whatever UE4 and others do.
That is true, my explanation is only limited to the x86 platform. Before you do any kind of threading, the first thing what you have to do is checking if the current platform the application is running on is atomic or not. I'm not saying that you should always avoid mutexes, but on boolean flags usually you can (depends how the system is designed). Note that mutexes are not for free (it costs more memory and CPU checks) and settings up mutexes on every (lets say 1000) booleans it could impact the performance.
@@robertenyedi5692 "Boolean value is stored on a signle bit (0 = false, 1 = true)" Bools aren't stored as a single bit (or even byte necessarily), and that's not relevant anyway. As ashutosh108 points out, the issue is with atomicity. Point 1 is valid though I think, probably... most of the time.
This was so helpful--thank you!
well explained, thanks for this awesome tutorial!
Thanks for another awesome video!
Thank you alot for your videos!
That was a really nice review! Thank you
i cant thank you enough, finally found what i needed
This is really good explanation for this.
Awesome video!
Can you do please videos about multithreading problems and how to avoid them? (data race, deadlock,livelock,starvation, etc.)
Great video, love wood scenery
Great vid as always
Locations behind looks so peaceful
Thanks Cherno
great tutorial!!! I love your videos
Note that simple thread example is actually wrong: it accesses a global variable (s_Finished) from two different threads without using proper thread synchronisation - which according to the C++ 11 standard is "undefined behaviour".
In fact, a C++ compiler is explicitly allowed to "optimise away" the read- access to the global variable s_Finsihed in your worker thread. Why? Because access to that variable is not using any thread synchronisation mechanisms (such as e.g. std::atomic), so the compiler is able to say: "Hey, s_Finished is never changed to false in this function call, so I may as well replace it with while(true)!". Of course also depending on the "optimisation level" that you set during compilation.
And you would end up with a worker thread that would never stop!
Also e.g. refer to the excellent CZcams video "Back to Basics: Concurrency - Arthur O'Dwyer - CppCon 2020". At around the time mark 6:45 it says: "Every write to a single memory location must be synchronise-with all other reads or writes of that memory location, or else the program has undefined behavior".
And that's why there's a bit more behind concurrency than simply spawning multiple threads ;)
But otherwise nice video that shows in simple ways how to create and join threads in C++ :)
If tutor is going in nature, why should we study in room, I'm watching this in nature.
Cherno you are amazing brother ❤️❤️
brilliant vid, thx
My game engine uses a thread pool that I've written along with coroutines for the different components and a scheduler class. The scheduler determines how long and when each component should run based on amount of work and priority and because they're coroutines its easy to suspend them at many points, save their state, and then pick up execution from there during the next frame
Cherno you are a hero!
hey charnya its amazing series
I love the fact that you are doing this in the forest!
It's easy to understand, thanks.
powerful for image processing
Finally. I am waiting this.
Need more videos in C++ series! :)
You should have mentioned Race Conditions which are probably the most common problem with threads. Still nice simple introduction.
Thanks for this comment. I didn't realize they are related.
@@NeoKailthas Yeah race is a big problem especially with different colored threads
@@puppergump4117 Whats thread coloring?
@@Henry14arsenal2007 A race issue lol
@@puppergump4117 lol i just only now got that it was a joke, legit thought thread coloring was a concept in programming (which i was hearing of for the first time in my years of studying and practice).
No mutex or atomic :/
I would also like to see thread synchronization covered.
@@warrenbuckley3267 me too me too
No std::future or std::async :/
He just uploaded a video on it
@@warrenbuckley3267 and thread safety, race conditions etc
love the birds in the background xd
if you print very fast, in background thread, and you don't use std::endl but you use
then it goes into new randomly.
"
" Outputs a newline (in the appropriate platform-specific representation, so it generates a "
" on Windows), but std::endl does the same AND flushes the stream.
The aussie forest background sounds were a vibe
Thanks!
very well explained.
Thanks for the great video! Can you please do a follow up video on how Future, Promise and Coroutines work in C++?
teaches threads in da woods. legend
awesome!
FYI open gl is single threaded
....
I use threads in all my heap allocations but I try not to have more than 2 threads running at the same time.
Also it's better to abandon oop and have your threads in one function with a switch loop, and each case calling a single function
(then the function calls the classes etc)
EXCEPTIONS Chernobyl
Thanks
thanks!
The code in this video is not thread safe, s_Finished should be atomic, it is perfectly acceptable for the compiler/machine to only do the read once for that boolean value if it can determine it is not changed anywhere throughout that function, in which case it won't see it become true.
Hey cherno loving this as always still waiting a course on algorithms and data structures
Awesome!
you are the best!
11:16 His camera man says "It's done?" :D
شرح حلو عاشت ايدك ♥👏
well said
I LOVE YOU AND YOUR CHANNEL IS FANTASTIC IM BRAZILIAN BRO
Nice forest!
i'm glad that modern PCs are multicore because in the old days, one could have threaded code that worked but only because all the threads were scheduled on a single CPU (i.e., software threads), getting discrete time slices and not truly running in parallel. The code would then fail on a multiprocessor system surprising the developer. But now we can rigorously test right away. Even release vs. debug builds can differ!
Hi cherno , please make video on recursion in c++ & how it works internally.
Threads! Finally!
I almost didn't recognize you until you did the hands :-)
I like the nature
AmaZING! Thank you. Now l can run 2 things together!
I work at home in a room with my pet birds, and they are going NUTS from the bird sounds in the background lol
9:26 does nobody want to tell me what that sound was
thas a phantom from minecraft
I would say that’s a jay (bird)
Probably a pterodactyl
That sound was made by a "wild cherno", it's a rare animal found in the woods who codes in C++.
Nature is so beautiful!
bigfoot
@TheChernoProject will you ever go in to true parallel programing without shared memory. Like how to use MPI for example?
More threading videos!
Thanks for the video, i wonder if boolean variable could be cached and never get new value?
Some questions i have:
- How would I make differents thread accessing and updating the same value to always have the most up to date value?
- And also, how many threads can I initialize? My pc has 16 threads, so is that the maximun I can start? Or if a start more than that the OS will handle how each thread will run?
Can this treads be used as Interrupt? My C++ project got safety concern. It need to do interrupt when safety button trigger. Then execute machine stop function & power down machine immediately.
why do you sometimes use "
" and other times use std::endl?
imagine hiking in woods and seeing guy speaking about threads in cpp
What is the advantage of using thread header over MPI or OpenMp?
That Resolution, oh boi.
subscribed
hey there, hoping for you thoughts on this. wish to make a fake 3d style fps rpg with a physics engine to help simulate abilities like telekinesis and such. wish to build from scratch though not sure of the mathimatical requirments to understand and anything else that would be needed. would be using c++ and not look to make it very complex just enough to simulate what i want. if possible? any suggestions or advice? would the sparky engine in your tutorials work for it?
fuck , he explained it so well
Nice
Isn't accessing the same non-atomic variable in two different threads wrong? (i know that you're only mutating it in only one of two threads, but still).
Nice video btw.
Thanks!