Semaphores

[@bagos1997]

If anyone is confused from the word Semaphore know that in Greek the word Σημαφόρος (Semaphoros) means Signal-bearer. Hope that helps.

[@omardumet120]

we call traffic lights "semaforos" in Spanish lol

[@shivamxsingla]

@@omardumet120 lol

[@sasankv9919]

Thanks, this opened up lot more meaning to this concept

[@manuelconte2127]

in italian "SEMAFORO"

[@189Blake]

@@omardumet120 Yeah, my language is Spanish and when I heard the concept it was rather logical to know what it does

[@murshedaziz3742]

This channel is a blessing. During my undergrad, I used to refer to your videos to clear out my doubts. Now doing the same in my postgrad. Why on earth teachers can not teach like this.

[@yajie7756]

Some teachers just try to talk for how long a lecture lasts...

[@shreyanshgupta1587]

Capitalized Education 👍

[@shamveerapan2875]

Cause they want to complete the portion.... they too want to make the students clear. ..but some can't because they dont know.. and many can't because they dont have much time.. they can give you only a outline...what to do???. Its out fate.. 😅😅😇😊😉

[@elmass3662]

NESO academy really be pulling through. Thank you so much sir!

[@abdelghanimoumen2524]

This perfect mini-course is better than my college's 10 hours course

[@asmaaasmaa2395]

Hahahah yep ,it's useful for the cs students

[@EnigmaAI-88]

True bro 😂

[@alokendughosh7013]

This presentation is too good. Understood it perfectly. Thank you so much sir❣️

[@rupambiswas953]

Became a fan of this channel, it saved my degree 🙏🙏💙💙

[@tanish_mavi]

Best explaintion of semaphoros on the entire Internet. Thank you so much sir

[@nojoodothmanal-ghamdi1026]

Thank you so much the idea is clear now, I cannot express how much you helped me

[@surajbhardwaj1200]

Best explanation on KZbin.

[@rohitkandula8493]

One an only king for Operating Systems🔥🔥🙏🙏

[@farahmohamed2104]

The session is too good. and precise Helps to understand very clearly. Thank you

[@mihneapostoaca5044]

You are a master,sir!Great job!

[@hetaeramancer]

Wow a new video on OS, finally I can continue my learning on OS that has begun since 2018 LOL

[@invinciblegirl4386]

😂😂

[@AbhishekGupta-vu7zt]

😂😂

[@NandhiniG-h6o]

So u took 3 years to learn os huh

[@ShainaSandhu]

​@@invinciblegirl4386😊😊

[@ShainaSandhu]

​@@invinciblegirl4386😊😊😊😊😊

[@sheikharooj5762]

I read it in book did not get any of the concepts but the way you have made the concepts easy for me..cant explain in words thank you❤

[@himanshusoni1512]

Djiktra himself explaining the Semaphore. Thanks

[@dharanyuvi6951]

Legendary explanation .., thank you champ

[@divyasrisatyavada965]

Wow what a explanation sir .I am very cleared about this topic after watching your video thank you so much for such a valuable information sir

[@medhananjay9099]

what an amazing explanation thankyou so much neso academy it is very heplfull !! thankyou again

[@kerematasen399]

Best explanation ever.

[@ahmedrateb5867]

Outstanding, makes it so easy and the way it s presented is great

[@abdi.]

thx dawg, gotta exam this morning. this really helped

[@nguyeninhan8542]

this is absolutely better than my university's course

[@kailas813]

The session is too good. Helps to understand very clearly. Thank you

[@stickkh4083]

I just understood clearly by watching your video thanks you

[@jaikishank]

Excellent and crisp explanation. Thank you.

[@captureit4410]

saviors for engineering students

[@adilmughal2251]

one of the best explanation.

[@goldenarmer6363]

God level explanation💥👌

[@tanzimhasan4464]

Thanks for this valuable video 💗

[@mriduljain6809]

Amazing Explanation Sir.. Thank you so much 💓💓🥰🥰

[@wizardop2100]

very well explained sir.Thank you so much

[@darshil-oh2le]

Nicely Explained 👌👌

[@coding_unicorn2]

Well explained 🧡

[@avishkarkurkute4753]

neso, you are saviour🙌

[@theomniking7856]

ive learnt more things from neso academy (and other youtube tutorials ) than in UNI

[@wasalawyer.1179]

And it is no joke

[@Ragehunter]

it is now clear to me, thank you so much!

[@puneethj9920]

Great video🙂

[@mohammadadrees5263]

Thank you sir. explained very well.

[@Account-fi1cu]

Thank you!

[@amrrelsheikh]

You didn't need to repeat "enter the critical section or use the resource" a hundred times, it was extremely disturbing, just pick one of them. But thank you, I finally understood the concept after I failed to in 2 different subjects at the uni.

[@BLG120]

it wasnt disturbing for me. it helped me to understand thoroughly.

[@aboudejeber1976]

Thank you sir , that's the explanation i was looking for 🌹

[@HabibiTau]

Best way to cover syllabus in less time is to watch your videos.

[@DopetheKid]

SIR YOU ARE GREAT

[@abrargadelrab8093]

well explained.

[@amanprajapati6301]

very valuable lacture for us thanks you 🤩

[@aiqabusov6926]

Great Content

[@jackeyboy6508]

Thank you Neso

[@khangpiano549]

Thank you

[@dnyaneshvarsalve2984]

very good explanation

[@nehasv7913]

really awesome.

[@GilbertJackob]

A lot Better than Gate Smashers

[@huhhzy]

i really appreciate you

[@fullstackcourse]

You're the best!!

[@YuganNimsara]

was really helpful. thank you very much.

[@balaganeshn4442]

Thanks a lot for your clear explanation , Is there any video for MUTUX?

[@fahedzidani2681]

instead of using var S u use mutex

[@Nilotpal_Chakravarty_]

Mutex locks are basically binary semaphores

[@MatheusSilva-dragon]

Damn! THANK YOU! You guys always help me!

[@bishnubhusal5999]

All the videos are great, only the lacking thing is coding part.

[@bakersisters7]

Best explanation ever🤌🤌

[@MiniduPunsara]

always the best

[@ripudamansingh6928]

sir you are the best

[@Bearded_Dragon_Sir]

Thanks!

[@mohammedparwes9760]

Hats off boss!!!❤

[@klaik30]

The point of mutex is to lock a critical section so that it is thread safe but the call for P() itself is not, right? If two processes each read the check for S they will both see that S > 0 and continue to both run S--. How is this accounted for? I dont think the video talked about this specific scenario?

[@luciddebz9510]

The atomicity of P() ensures that race conditions do not occur when multiple processes/threads attempt to decrement the semaphore simultaneously.

[@himansushaw4938]

very nicely explained. Thanks

[@DonaldMurf]

Thank you so much for this video.

[@venkataswamykadiyam977]

Sir, please upload remaining videos in youtube. We can't be able to take screenshots of the lectures in neso app to revise them whenever we want...

[@kavyabanka4482]

Please send memory management in you tube not only in neso fuel please release in u tube

[@mughatoamugha9029]

🙂 hi.. holaaa... Good to be here again 😇

[@leducphuclong]

Thank you so much !!

[@KarouiFulla-m6e]

thank you so much brooooooooooooooooo

[@patiencechiripanyanga7385]

Well elaborated

[@shifankphoulad]

Nice 😊☺️👍👍

[@iyadassaadnekka329]

Very very amazing thank you

[@Whymysolutions]

Really it's awesome

[@Pokehunter-t2f]

Plz upload all lectures on youTube 🙏

[@eswarpethraj9099]

In counting semaphores, if S is set to 4, then 4 processes enter the critical section at the same point of time, how it's possible because only one process can access the critical section. And what do you mean by an instance of a resource? Any example with c++ 20 code using counting semaphores.

[@subbumotepalli]

Same doubt .if you know plz explain

[@apurvkumar1808]

S is set to 4 means there are 4 instances of the resource so 4 processes can enter in critical section at once.

[@wasalawyer.1179]

does that violate Mutual Exclusion principle?​@@apurvkumar1808

[@aribiali3574]

I luv u dude 💙

[@Lawleit_L]

But what is the different between locks / semaphores and the other algorithms that we have seen like FCFS, RR and SJF , because all of them are synchronize and arrange the prosses.

[@ashishchawla9035]

But as the critical section can only be accessed by one process at a time so how two processes are entering the critical section at the same time and using it in counting semaphore?

[@ahmedrateb5867]

Counting semaphores are a generalisation of binary semaphores, whereas binary allows a maximum of 1 process to enter the critical section, counting allows up to n where n is a positive integer

[@SOWProgramming]

Counting semaphores are used when processes need to access a resource which has n instances, so N processes can access that resource.

[@kusalaphameya3421]

so amazing

[@muhammadmaawaz1221]

Thanks

[@Makerelax444]

IN COUNTING SEMAPHORE : Two processes goes to critical section at same time then it disobey mutual exclusion. How it is a solution

[@LL-oj3cs]

Truly thanks from an OS final headache person

[@eylulmood4830]

why test and lock is a hardware solution? we also used a variable Lock, whereas semaphore is software solution

[@rohith2758]

Worthy video

[@sudhakannan4746]

Thank you sir..

[@samarthtandale9121]

To prevent/protect a shared resource from being accessed by multiple processes at the same time we use Semaphore S, and wait() and signal() operations. But for wait() and signal(), again, the Semaphore is shared resource and they have critical section in them, so we have to again implement mutex for Semaphore S and so on. So, If you got what I just said, to solve a problem of mutex, we are generating another problem of mutex and that will recursively generate another and so on... So how do you solve this problem or where exactly did I go wrong?

[@Mehraj_IITKGP]

You are correct that using a semaphore to protect a shared resource can introduce its own synchronization issues, particularly if multiple threads or processes need to access the semaphore itself. This can lead to a problem known as "semaphore contention," where threads or processes contend for the semaphore itself, rather than the shared resource it is protecting. To address this issue, it is important to carefully design the critical sections for the semaphore and ensure that they are as small and simple as possible. In particular, the critical section for the semaphore should be limited to the code that directly modifies the semaphore's value, such as the wait() and signal() operations. One common approach to minimizing semaphore contention is to use a variant of the semaphore known as a "spinlock." A spinlock is a type of lock that repeatedly checks the value of the semaphore in a loop until it becomes available, rather than blocking the thread or process. This can reduce the overhead of context switching and thread synchronization, particularly in high-concurrency environments. Another approach to reducing semaphore contention is to use techniques such as "reader-writer locks" or "lock-free algorithms," which are designed to allow multiple threads or processes to access a shared resource in a more fine-grained and efficient manner, without relying on traditional locks or semaphores.

[@samarthtandale9121]

@@Mehraj_IITKGP Thank You very much for taking time to resolve my doubt !!!

[@samratpatel8060]

@@Mehraj_IITKGP wow , wrote an long ass para for solving a strangers doubt

[@uditish5531]

Just perfect!!!!

[@heysisteronion]

thank you^^

[@minidupasan1520]

[@dodsa247]

I think the definition of wait() is Wait(S){ while s>= 0; s--; } in the video it is Wait(s){ while s

[@JanhaviDeore]

s

[@codingwithazan2280]

You missed the concept i would say

[@chhajedji]

What if s=1, hence both P and V execute simultaneously and during s++ and s-- we face the original producer consumer problem and instead of s being 1, takes value 0 or 2?

[@vinayak186f3]

Why is there no while loop in signal's def. i mean if it's a binary semaphore and is already 1 won't it overflow ?

[@diptabose7187]

S never exceeds one in binary semaphore , because to access the critical section wait operation is done. And after accessing signal operation is used . As signal and wait operations are used indivisibly , Semaphore value doesn't overflow , it remains between 0 and 1.

[@MrAmalthejus]

How can a Resource have multiple instances?! What kind of Resources are you talking about?

[@MrMaschine999]

Why is it possible for different processes to be in the critical section for counting semaphores? I thought you sad we only want one process at a time in the critical section. Did I misunderstood something?

[@harshmishra9008]

Is there any platform to get the notes of the lectures?

[@amillion7582]

damn, my professor literally took months to explain this simple concept

[@somethingnew3654]

In counting semephore..mutual exclusion is not followed..then how is it solving critical section problem?

[@lowerbound4803]

How could we ensure that S will never be altered from different sources simultaneously?

[@raaj7256]

It's because they're atomic. I guess they're internally atomized using test_and_set or compare_and_set, and my faculty told test_and_set and compare_and_set cannot be called at the same time, there for you can't really call them at the same time (Don't know if the "cannot be altered part" is correct though).

[@lowerbound4803]

​@@raaj7256 Thank you for your answer!! I have to learn how atomic works.

[@decostarkumar2562]

It's wrong. In semaphore loops are not present. To avoid busy waiting symbols are used .