What is a mutex in C? (pthread_mutex)

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yup

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Exactly

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The operations performed by a thread after acquiring a lock are called "critical section". This helps in achieving thread synchronisation. Thanks for the video!

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Can’t thank you enough for your detailed and succinct explanations! When I began diving in to multithreaded programming with C++17 I became overwhelmed pretty quickly

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you should train professors on how to teach Thanks for explaining, it was very easy to understand.

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[@triplestrikee875]

The lock variable + if block example is the best example I have even seen for this Mutex topic

[@harshmishra9941]

I purely watched this playlist to understand what the heck my OS prof was teaching when she taught us semaphores (although for processes) and I couldn't understand at that time. Loved it !

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Hello. This is one of the greatest tutorials I've seen. I will be watching the whole playlist, thank you for your hard work and skill in education.

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You saved alot of work and misunderstanding with the threads videos. Thanks alot

[@DeezNardsX]

Just a slight correction at the end: You can have race conditions on single core processors. We can fake "parallel execution" by time slicing. If the two threads are sharing memory resources, then we can absolutely have a race condition during a context switch.

[@CodeVault]

That is correct.

[@ManaswiRaj-p8u]

Race conditions can also occur on single core processors like if we consider concurrent CPU and the operations are read, increment and write. So lets say P1 starts first then P1 reads increments and then it is preempted by another process P2, then P2 does read, increment and then it is preempted by P1. Now P1 writes the value and exits after which P2 comes and writes its value thus there is a race condition

[@CodeVault]

You're right, I didn't want to go into much detail regarding this and gave a simple (albeit wrong) explanation

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You can tell how helpful his videos are because I have not seen 1 dislike yet. You make this so understandable

[@ndf782]

Your classes are amazing! All of them! Just one thing, I think that when you say race condition, the correct term is data race. Cheers!

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thank you really , you are better than almost all the teachers in this world... all the respect

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Best course on Multithreading!!

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Haha, thanks. I will think about launching some merch if enough people want them

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Thank you sir, these tutorials have made my synchronisation concepts very clear.

[@sanguinho]

What a clear and simple explanation. Thanks my dude

[@iloveukraine-subscribe1kgo822]

Thank you for the practical Mutual Exclusion video.

[@msimamsima9059]

Mutual Exception.

[@barankaplan4308]

PERFECT! looking forward to see a video about spinlock!

[@Achao3_AkaoShiro_]

Great video, explained how lock and unlock work really well. I was having trouble understanding what it was with my professors explanation lol. Thanks for explaining it, you definitely deserve more views and subs!

[@yernarduisebai5609]

You explain way more clear than my professor Park

[@izharhussain7241]

you are a gem! Thank you for the videos.

[@ayoubrayanemesbah8845]

just a note mutuale exclusion problem can heppen even for single core processors , because when the quantum ends of a processoes , another process can modifie the variable

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Great job. Explanations are easy and clear, very useful information. Thanks a lot!!!

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[@tiemen88]

Thank you so much for the explanation on Pthread mutex!

[@alireza98325]

Great tutorial. I have one comment about the likelihood of race condition happening for single-core processors. Even with a single core and a single processor but multiple threads (as it is the case for the FreeRTOS OS in embedded systems), race conditions will happen more often than not without a mutex, atomic instructions, etc.

[@CodeVault]

Thanks! Interesting. I wonder now about single-core single-thread environments. Technically there still should be some race conditions but they might be encountered less often. Would you like to test that?

[@alireza98325]

@@CodeVault I think the only possibility for race conditions to happen for single-core single-threaded app, is when a hardware interrupt occurs and ISR gets executed. If hardware interrupts were not present, I'm not sure race conditions can ever occur for a single-core, single-threaded app

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Foarte bine explicat, mersi :)

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Thanks for the great explanation!

[@ivanleon6164]

race cond can also happen in single core if interrupts are enabledand a variable is modified.

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many thanks for this series, sir! you'v saved me !!!!

[@galkk3]

I really enjoy your videos, thank you Could you make a video about Condition Variables with threads?

[@CodeVault]

Will do

[@log_of_1]

Really a wonderful explanation. Thank you!

[@patrykjaworski402]

I love your videos. Your materials are helping me a lot more than my lecturers do and also you making it simple and more understable. Looking forward to POSIX/ SYS V semaphores. Also I would like to ask will there be coming more materials about pthreads ? ( maybe private data of threads). Best of regards code vault. Keep it up!

[@CodeVault]

Thank you! And yes, the last lessons in the course are not yet decided so will add most of the suggestion from the community there (like this one ;) ).

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Fantastic explanation!!! Thanks

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AMAZING TEACHER!!!!!!!!!!!!!!!!!! THANK YOU!!!

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thank you for this playlist

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This is beyond helpful! Thank you so much :)

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Thank you sir , I appreciate your help !

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Thank you so much for the video!

[@jong.4864]

Thank you, you're so helpful!

[@msimamsima9059]

Very useful video! Thank you!

Could you make a video about semaphores and pointing the differences between it and mutexes' use cases?

[@CodeVault]

Yep, semaphores and barriers are also planned for this course

[@dorianalary7849]

Its incredible, I'm French but I understood perfectly this video, thanks you

[@AsliArtistVlogs]

Race codnitions can very well occur in single core processors too. Think of pre-emption.

[@timonburkard3481]

Exactly.

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Ty for the awesome videos!

[@cindaellas]

great video! thanks!!!! very good job! greetings from germany

[@chaimaeelhaimer870]

Bravo ! thanks for explaining my question is : when we may need to create 2 threads with same function?

[@CodeVault]

Whenever you want to split CPU intensive work between the threads, that's when the workload is exactly the same except for some indices.

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Really useful videos, just as im learning this at school :D

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[@Jonathan-ru9zl]

amazing explanation.

[@Alexander_444.20]

great explanation thank you!

[@Brad_Script]

Apparently there's another way of initializing a pthread_mutex: pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; I wonder what the difference is

[@CodeVault]

They are basically the same. The first one could technically be faster since it only assigns some values but can only be used. Also, it guarantees that the lock is always initialized

[@viniciuss.9250]

Thank you SOOO MUCH.

[@narasarajv5278]

Real time example super explanation.

[@peerapatratanachartchuchai5844]

Thank you for your great video bro. You save my life !!! Just curious a little bit from the last video. Base on my understanding, Race condition happen when 2 thread read memory at the same time. Is that possible if mutex lock data in exactly same time and race condition happen. If not why?

[@CodeVault]

First things first: a race condition happens only in two cases: 1) You have one thread writing a piece of data while other threads are reading it 2) You have multiple threads writing the same piece of data Two threads reading the same piece of data won't cause a race condition. Although with mutexes a read and write could happen at the same time, they are designed so that each read and write on them is atomic, meaning there's no way other threads could read the data while another is in the process of writing it (only before it wrote to it or after that)

[@austinoquinn815]

Maybe a minor misstatement when you say race conditions only happen on multicore systems. I think race conditions can also happen on one core processors. You could save your mails in thread 1 context switch to thread 2 and finish loop then go back to 1 and finish, then your result would only be 1,000,000 on write back. Great content though. Love this playlist.

[@CodeVault]

Yes, it's definitely wrong. Race conditions can happen on any system. It's just much much rare to happen on single-core processors as the context switch would have to happen right between an assignment (which, from what I recall, is a very low chance). Maybe I will make a video on this topic to investigate what is the chance of that happening and whatnot

[@austinoquinn815]

@@CodeVault that would be awesome 👍🏻

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Love your Videos

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Thank you.

[@misterSaragi]

Your a gem!

[@johnthompson4011]

Bro small problem with your code.I took this as a refresher to threads.Locking and unlocking the mutex in each iteration of the loop introduces unnecessary overhead and reduces the potential benefits of multithreading. A better way is to lock and unlock it outside the loop.Anyway thanks for the video bro

[@CodeVault]

Of course. But this was a short explanation and I wanted to show that the mutexes work even if multiple loops are executing at the same time. In a production environment, this would be very inefficient indeed

[@sakkamouid3343]

I think using lock the execution of the program would be slower, but that is not important . More important is avoiding race condition

[@wisiw]

Yes but doesn't that mean we're forcing multithreading program into serial program?

[@anthonymarcovecchio5201]

Good stuff my friend

[@dattakunal]

Thanks for the wonderful video. I have a question. What happens if thread 1 throws an error before the unlock? Will thread 2 wait forever?

[@CodeVault]

The lock is released, so thread 2 won't wait forever

[@oguzhanasilturk5110]

man, i wanna be your thread. such a good explanation

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good explanation!

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Great work

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Your video is the best. thx

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Could you please make a video about marge, selection, bubble and quick sort in c?

[@CodeVault]

Will look into it... may come at a later time tho

[@Edvs3261]

@@CodeVault thanks!

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Thank you! :)

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Thank you

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very underrated

[@kamurashev]

I believe it’d be fair to at least mention that there are other options to approach this. Eg in this example atomic would work better.

[@CodeVault]

You mean atomic operations?

[@kamurashev]

@@CodeVault yep, like using atomic_int eg

[@spellignerror8998]

2:09 what if the threads met a race condition at reading lock?

[@CodeVault]

locks are thread-safe at the OS level

[@wisiw]

Can we say that mutex locking forces the multithreading routine into serial?

[@CodeVault]

Yes. Basically the critical section that is surrounded by a mutex lock/unlock will always be serially executed

[@DineshKumar-wo4tj]

Even if I comment mutex_init and mutex_destroy, i can able to see mutex lock/unlock is working. Then what is the use of init/destroy function???

[@CodeVault]

Well, init is surely needed when using a mutex. Although, probably, since the mutex is global in this video it gets its members automatically initialized to 0 and I think that coincides with what pthread_mutex_init sets the values to. If you try to use the a local mutex I think you'd have issues without the init function call. The pthread_mutex_destroy is not 100% necessary on some architectures but it's good practice

[@DineshKumar-wo4tj]

@@CodeVault Thank you for your clarity.

[@selvamthiagarajan8152]

say in the routine() function I had 3 different operations, op1, op2, op3. I place a mutex_lock before op1, mutex_unlock after op1. Assume 3 threads. Will the other threads execute op2, and op3 when op1 is under lock ?

[@CodeVault]

No, they won't. All threads will wait at the mutex_lock instruction until the lock is unlocked. Though, this still allows for race conditions on op2 and op3