Method parameters are also located on the stack. If a parameter is an object reference, the reference is passed on the stack whereas the object remains on the heap. Also checkout my video about the Java Happens Before Guarantee - which is also part of the Java Memory Model: kzitem.info/news/bejne/0I9nmomviWhieW0
@amalangelraj
2 жыл бұрын
Im your fan, love you so much for your help. You are the only reason for i am learning java! To express my grateful respect, I subscribed you. Once i get job i will support you and will help you as much i can! I am seeing in each video how much sincere hardwork you put in these tutorials! Salute from tamilnadu, im living in pattukkottai a small town! Im a first graduate in my family! I will also help like you in future selflessly.
@kamranvlizad3862
2 жыл бұрын
Man, in the beginning of the playlist I thought it would be some generic tutorial about threads. But I was so wrong. This here is just pure GOLD. Thanks, Jakob.
@JakobJenkov
2 жыл бұрын
Hi Kamran, I am happy that you did not get disappointed :-) I have tried to really get "under the hood" to explain how threading works inside the Java VM. When you understand that, multithreaded programming gets a lot easier, and more predictable :-) ... I have a few more videos coming in this playlist in a near future. Hopefully some of them will be useful for you too :-)
@aayushmanmishra1425
24 күн бұрын
You explain so well. I have been your follower since college, and now I am a software engineer. Great work, really appreciate 😊
@JakobJenkov
24 күн бұрын
Thank you very much for your kind words :-) I am happy that I have been able to help you! :-)
@Shivam-wk6sq
2 ай бұрын
One of the best tutorials out there.. This is literally a goldmine.. Thanks a lot
@JakobJenkov
2 ай бұрын
Thank you very much !! 😊
@fuadgafarov
3 жыл бұрын
I am never see such detailed explanation about threads as this. Thank you Jakob. Pls never remove this videos. We would need it until lifetime)
@JakobJenkov
3 жыл бұрын
Thank you very much - glad my video helped you :-)
@user-sp7kp9mo1q
Жыл бұрын
This playlist is super helpful, I rare to find who explains practical parts linked to theoretical parts without too much abstraction or too much detail, it is just the optimum explanation
@JakobJenkov
Жыл бұрын
Thank you :-) ... yes, I try to explain the theory in a way that a practitioner needs to know it - not like some academic would phrase it ;-)
@prakritidevverma4315
3 жыл бұрын
Oh man.... your explanation is so good. I'm preparing for my java interviews and you have covered a lot of stuff in your playlist. Thank you for helping the community. 😬
@JakobJenkov
3 жыл бұрын
You are welcome!! :-)
@jayasribhattacharya2048
4 жыл бұрын
you deserve more subs. your vids are awesome.
@JakobJenkov
4 жыл бұрын
Thank you very much :-)
@MrPersistent16
4 жыл бұрын
Agreed!
@RoadRoller01
3 жыл бұрын
Agreed! !
@bharatjain90
3 жыл бұрын
Your videos on multithreading are the best explanation I have come across in 20 years of java exp.
@JakobJenkov
3 жыл бұрын
Thank you very much for your kind words! :-) Glad the tutorials are helpful!
@mondofps
3 жыл бұрын
Your tutorials are absolutely fantastic and have taught me so much, thank you.
@JakobJenkov
3 жыл бұрын
I am happy to hear that :-)
@isahilliogluu
3 жыл бұрын
It's so admirable and appreciable that you don't prefer to show ads in your videos. Your videos are concentrated and distraction free. Big thanks Mr. Jakob.
@JakobJenkov
3 жыл бұрын
Yearh, I only have ads before and after... and sometimes a bit of overlay ads which you can remove yourself. I only have these in-video ad breaks in very long videos - and not in everyone of them.
@michaeldemarco82
2 жыл бұрын
Great Job Jakob, I have been architecting and developing for over 30 years and I can tell you that you really cover the permutations of what can happen and explain each use case and your use case granularity is noted how you depict how memory is shared or not based on instance or static or shared instance passed into the thread. Your methodology makes sure people have the info to get it. you don't talk bits and pieces you do a comprehensive covering and I hope people understand and appreciate your level of definition and 360 degrees of dimension which produces "understanding"
@JakobJenkov
2 жыл бұрын
Hi Michael - thank you ! ... that is exactly what I am trying to do in my articles and videos - to provide that core understanding that enables developers to "calculate" how a given piece of Java code will behave in different situations. Predictable code gives developer confidence too. Unfortunately it often takes me a long time to figure out how to best present a given topic to provide that core understanding - meaning I don't publish as often as I would like to!
@snoz9048
2 жыл бұрын
Jakob Jenkov the level of care and detail you put into your content - videos and written tutorials alike - is absolutely mind blowing and inspiring. Nuff Respect.
@JakobJenkov
2 жыл бұрын
Thank you very much for your kind words! I appreciate that! And - I am happy that you find my videos useful :-)
@shubhamagarwal1434
3 ай бұрын
God of Concurency..i have bene flowing you since my 2014 when you used to write blog post only...by going through your post i attend interview like a LION when they ask mutithreading qns.......Thanks a Lot form 10+ yrs exp guy from BLR,India.
@JakobJenkov
3 ай бұрын
Thank you for your kind words ! :-)
@mostinho7
3 жыл бұрын
Thanks done 18:30 example on when threads will be sharing a variable vs each having its own variable. Think of the Runnable like any other object, if the same one is passed to different threads then variables declared inside that runnable will be accessed by the threads. If a new runnable or new object is created for each thread then they will be accessing completely different objects
@manOfPlanetEarth
2 жыл бұрын
nice addition.
@RC_1930
2 жыл бұрын
I'm preparing for the OCA exam, and this was exactly what I needed. I thank you Jakob from the bottom of my heart.
@JakobJenkov
2 жыл бұрын
You are welcome! ... remember to also watch Part 2 about the Java Memory Model - the Happens Before Guarantee video!
@manOfPlanetEarth
2 жыл бұрын
@@JakobJenkov hm🤔 maybe it's reasonable to add "part 1" to this video title?🙂 bwt, it's very practical to add whole playlist link in video description (U did that). It's very convenient.
@matthewsaucedo2471
8 ай бұрын
Most any software engineer has watched, for myriad topics, hundreds of instructional videos. I must say that you are in the top tier of informational content producers. Your pairing of diagrams with code, and references to both throughout, is excellent. You do a masterful job of relaying complicated concepts to viewers with efficiency. Hats off to you!
@JakobJenkov
7 ай бұрын
Thank you ! ... I do spend quite a long time trying to figure out how to explain a given topic best. That is one of the reasons I do not make so many videos :-/
@rohitk9221
3 жыл бұрын
This is the best explanation for threads on the internet and even in the libraries of the entire world!
@JakobJenkov
3 жыл бұрын
Thank you very much :-) ... remember to also watch my follow-up video "The Happens Before Guarantee" - to fully understand the Java memory model !
@reynaldolibutan8468
2 жыл бұрын
this tutorial and how you slowly present your ideas with examples is too underrated! You need more subs, views and exposure in general!
@JakobJenkov
2 жыл бұрын
Thank you Reynaldo :-)
@samuel2560
3 жыл бұрын
Great explanation. Finally, I understand how local variables work with threads and why it is important to keep this in mind trying to solve race conditions in Java concurrency. Greetings from Mexico!
@JakobJenkov
3 жыл бұрын
Thank you ! ... Greetings back - from Denmark :-) ... I am happy my explanation helped you! ... I spent a lot of time studying this too, when I started with Java. Also, some of the details changed over the years... that's just part of the game :-)
@manOfPlanetEarth
2 жыл бұрын
@@JakobJenkov Denmark! aaaah, you're not english native:)) i guessed that while reading articles on your site. Very often very bad sentences structure:)
@michaelhughes8413
3 жыл бұрын
This is a really useful discussion of a difficult topic. Clear code samples, nice diagrams and well paced verbal explanations. I admire your ability and efforts to spread knowledge. Thank you so much!
@JakobJenkov
3 жыл бұрын
You are welcome! ... in my experience, the most occurring reason why people have a hard time learning some new topic is learning materials that are hard to understand. I am trying to rectify that - to the extend I have the time!
@kzelmer
Жыл бұрын
Best explanation of Java concurrency hands down. Thank you Jakob
@JakobJenkov
Жыл бұрын
Thanks ! :-)
@mtqin2956
3 жыл бұрын
Any knowledge written in your blog is very important to me ,i have never found a engineer who written the same content better than you,thanks +
@JakobJenkov
3 жыл бұрын
Thank you very much for your kind words! I am happy that my tutorials are understandable! ... hard-to-understand material is a real set-back for developers learning new tech!
@arjunmsit
Ай бұрын
Really appreciate the video for nicely explaining the concepts and internally how it works... Unfortunately most of videos just say what is multi threading and how to implement but don't talk about the it works internally.. Thanks a lot for helping me understand multithreading better ❤
@JakobJenkov
Ай бұрын
What do you mean by "works internally" ?!?
@dhruvankadavala568
12 күн бұрын
Best explanation I have ever seen...
@JakobJenkov
10 күн бұрын
Thank you very much !! :-)
@AbhishekVaid
2 жыл бұрын
1 subtlety which is missing from this video is the distinction between "Thread Stack" and "Call Stack within the thread stack". At 2:07, while it is correct that local variables are stored on Thread stack, they are actually stored on a call stack within the Thead stack. A call stack encapsulates the execution state (local variables, return values, program counter ...) of the currently running function.
@AnkitKumar-zu7cn
Жыл бұрын
Bit confusing. A call stack entry only stores the primitive data types and the object references. The actual object is stored in the heap. However, here he mentioned that the thread stack contains the object (and not the reference).
@JakobJenkov
Жыл бұрын
If I actually do say that - it's a mistake. Only the object reference is stored on the stack. The object is stored on the heap. However, at the exact time in the video that is referenced in this comment - I clearly show in the diagram that only references are stored on the stack - and the object itself is stored in the heap. And - I also explain that in the video, right there.
@thomasrixen5390
2 жыл бұрын
Dude you have the most relaxing voice of all time. I have trouble getting sleep in general, so I code at night when I can't sleep. But you make me sleep in 5minutes
@JakobJenkov
2 жыл бұрын
I am not sure if that is a good thing - or a bad thing ;-)
@ashutoshkedar1577
3 жыл бұрын
You are the most amazing tutor I have ever had. Kudos to your teaching skills.
@JakobJenkov
3 жыл бұрын
Thank you very much! :-D
@hongzhanglin6245
11 ай бұрын
thanks you Jakob, I hadnt see tutorials like yours ever. your tutorials are simple and easy to understood, i like it.
@JakobJenkov
10 ай бұрын
Thank you very much !! :-)
@jvsnyc
4 жыл бұрын
Yeah. This is fantastic. A lot of presentations are pretty superficial and get people writing and starting multiple threads, but not realizing the data hazards due to shared memory. When I first played with multiple threads, I even thought I was aware of those, but would sometimes see anomalous results. I think going slowly and carefully in the first long part of the video showing what is shared and what is separate is very important in that regard, instead of just jumping into synchronized and volatile in a big hurry.
@JakobJenkov
4 жыл бұрын
Thanks - I was actually about to upload the video without the first, detailed code walk-through... but then I decided that such an example was necessary!
@eduardojavierlatorrevandep4583
2 жыл бұрын
I really appreciate all the details you give out in your tutorials! I've been learning so much with you... keep it up :)
@JakobJenkov
2 жыл бұрын
I am happy to hear that! :-)
@FABGIO1
Жыл бұрын
Your explenation was absolutely clear. It throwed light on thread race condition that I had been struggeling for years to understand proprerly, even after reading "Cuncurrency in Practice" Goetz's book ! Thank you so much!
@JakobJenkov
Жыл бұрын
I am happy to hear that!!! ... you are very welcome! :-)
@ripusudan100
2 жыл бұрын
jakob i follows you from starting of my career...your tutorials are clear and well explained!!!
@JakobJenkov
2 жыл бұрын
Hey ! Great to hear! :-) I am happy that my tutorials are useful to you !! :-) I have had a bit of a "break" - or "slowdown" as I am trying to figure out what to write about going forward, so I write about something that is both useful to others, but also something I learn from myself, and find interesting myself. But I think I have figured that out now... so I hope to speed a bit up again within the next year or so.... within reason - because I also have a full time job to attend and other things :-D
@nabeelahs9588
3 жыл бұрын
So happy to see you have a channel. I've been using your tutorials online and they're awesome.
@JakobJenkov
3 жыл бұрын
Thank you very much! I am happy you found my channel then! :-)
@bahaagamal4995
4 жыл бұрын
You are very good in arranging and describing the information. Very nice video.
@JakobJenkov
4 жыл бұрын
Thank you very much! I've got a sequel to this video coming up which explains more advanced features of the Java memory model: The Java Happens Before Guarantee for volatile variables and synchronized blocks.
@xixia1597
3 жыл бұрын
At 22:22 , Thread 1 is 2 million but Thread 2 is not. I tested this locally and I see the same discrepancy. On multiple runs, a few do result in 2 million in both. I did fix it by using a CyclicBarrier right after the end of the for loop. So apparently making sure both threads do the full for loop matters. My guess for the different counts is because one Thread (it could be 1 or 2 it seems, from testing) starts just a bit before its partner. While late thread starts and is busy incrementing the count, the initial thread has already finished its for loop and prints the count. Since, the late thread hasn't completed its for loop, the counter isn't going to be 2 million yet. Then the late thread finishes and prints - this will be 2 million.
@JakobJenkov
3 жыл бұрын
Hi Xi, if 2 threads both count to 1.000.000 - the total result should be 2.000.000 - but both threads will most often NOT reach the final count at the same time. One of the threads will typically finish its 1.000.000 iterations before the other, and thus the total count at that time is less than 2.000.000 .
@roman_mf
2 жыл бұрын
Thank you Jakob for all your efforts and shared knowledge. With your videos learning such complex topic is a breeze!
@JakobJenkov
2 жыл бұрын
Great !! :-)
@aaronrasing2710
2 жыл бұрын
Third episode in and I really find your tutorial and examples really comprehensive. You use words and examples that are so easy to understand. I've been trying to get my head in concurrency for quite some time now and this is by far the best tutorial I've seen. One improvement - perhaps it would be nice to have your examples in git.
@JakobJenkov
2 жыл бұрын
I have a few of the examples in a git repo here: github.com/jjenkov/java-examples If you browse the code, there are more examples than what are listed on the README page.
@tomok284
Жыл бұрын
Few tutorials will link it to the hardware. You are doing a great job!
@JakobJenkov
Жыл бұрын
Thanks !
@mehtubbhai9709
5 ай бұрын
More Java tutorials please! 👍
@JakobJenkov
5 ай бұрын
I will try ! :-)
@AvinashKumar-tk5bd
6 ай бұрын
Guruji @jakobJenkov no words to describe.you made this complicated topic very easy.Thank you saw muchhhh
@JakobJenkov
6 ай бұрын
Thank you very much! :-) I am happy my video has helped you!! :-)
@MarceloAX
8 ай бұрын
Very good explanation! Good level of depth knowledge about Threads and CPU arch! Congrats again for the great summariazation!
@JakobJenkov
7 ай бұрын
Thank you! :-)
@lewallen1971
3 жыл бұрын
Your videos and website tutorials are just fantastic! Thanks!
@JakobJenkov
3 жыл бұрын
Thanks! :-)
@KratosProton
Жыл бұрын
Great explanation!
@JakobJenkov
Жыл бұрын
Thanks :-)
@ritwikkumar1402
3 жыл бұрын
Lovely Explanation, Superb please keep doing the good work :) Came here from you blog and I am glad I watched this video. Just subscribed you and now i know where i need to end up in case i am stuck in java
@JakobJenkov
3 жыл бұрын
Thank you very much for your kind words! :-)
@guptatushar86
3 жыл бұрын
Thanks a tonne once again i so wish i could work with you to get these concepts (&Java) in my blood.... like day-in day-out ... the way we breath - that's how we perceive the concepts are to you ! Cheers !
@JakobJenkov
3 жыл бұрын
If you study and practice enough, little by little you will learn more and more and more. That's how I've learned what I know. Reading. Making small examples. Going to work and using what I learned. Reading more. etc. etc.
@hliebhalunko5214
2 жыл бұрын
Awesome tutorial! Thanks for your work! Though, it left several questions: 1. 22:56 - if Thread 2 finished first, why is it printed second? 2. It would be awesome if you mentioned the reason of different counts printed (while it is the same variable in memory) - while first thread is finished counting and printed count the second one is still uses that same variable and increments it. It's a matter of execution time. The combination of these two got me puzzled for some time :)
@JakobJenkov
2 жыл бұрын
Concurrency will get you puzzled from time to time in any case :-D ... still happens to me too sometimes ;-)
@ASTATEPACH
2 жыл бұрын
I think it's because Threads have a nondeterministic behavior in where external/internal conditions could affect the way your thread produces.
@alexs9289
3 жыл бұрын
Awesome videos, as other people stated. Keep them coming, your work really helped me understand concepts that other teachers couldn't explain !
@JakobJenkov
3 жыл бұрын
Thanks - will try :-) ... which teachers?
@user-kz4jr9ti4x
Жыл бұрын
Thank you Jakob, nice explanation
@JakobJenkov
Жыл бұрын
Glad you liked it ! :-)
@Sunsets_LoFi
3 жыл бұрын
Dude your explanation is awesome. Thanks for that quality of content. Please keep going
@JakobJenkov
3 жыл бұрын
Thanks! :-) ... I will continue - when I have time :-)
@aelkelaany
3 жыл бұрын
Thank you Jacob for this pretty clear explanation , good job
@JakobJenkov
3 жыл бұрын
You are welcome! I am glad it was useful :-)
@shreyasgosavi9647
Жыл бұрын
Woww!!! That was a very good explanation .. learned a lot in a single !! video over to the next one ;)
@JakobJenkov
Жыл бұрын
I am happy to hear that! :-)
@evgenyleshok5892
11 ай бұрын
Thank you very much! Your explanation and examples are really helpful. I wish you the best and motivation to create more such good content!
@JakobJenkov
10 ай бұрын
Thank you very much ! :-)
@maksymmatlo4327
3 жыл бұрын
English is not my native language but I can understand this video better rather than some videos about the same subject on my native language!
@JakobJenkov
3 жыл бұрын
Thanks :-) ... after 20+ years of working and learning in the IT industry, and 15+ years of blogging, I have realized that there is more to a good presentation of a topic than the language it is written in. My mothertoungue is Danish, but there are simply not enough materials available in Danish, so I've had to read it in English most of the time. And there is a big difference between a bad Danish book, and a good English book and the other way around too. Especially academic books can be hard to read - especially when written in a language other than your mothertongue.
You explanation is awesome. I want to be like you one day
@JakobJenkov
2 жыл бұрын
:-D ...you can become better than me! There are so many learning resources available today, that you can learn much faster than I could when I started out!
@theunusual4566
2 жыл бұрын
Thank you so much Jakob for creating such wonderful videos and presenting them in so easy to understand way.
@JakobJenkov
2 жыл бұрын
You are very welcome :-) Glad my videos help you! :-)
@paulisaichuk5034
Жыл бұрын
Thank you for the video!
@JakobJenkov
Жыл бұрын
You are welcome!
@MeftahLakehal
4 ай бұрын
Good explanation, thank you Jakob!
@JakobJenkov
4 ай бұрын
You are welcome ! :-)
@manOfPlanetEarth
2 жыл бұрын
nice, nice lesson. read a few lessons in text, now am covering them with video. can notice video is more detailed.
@JakobJenkov
2 жыл бұрын
Thank you! Great to hear! :-)
@manOfPlanetEarth
2 жыл бұрын
@@JakobJenkov really nice job, man. detailed. not in a hurry. it's a creative trace of your life. wish i will make something like that.
@rishabgoyal6138
3 жыл бұрын
This really good content low level java understanding with coverage of multithreading.
@JakobJenkov
3 жыл бұрын
Thanks :-) ... I try hard! ... though it's not that easy to find precise information about these topics, so it's not that fast to make videos about!
@flamencoag
2 жыл бұрын
Thanks a lot Jakob!
@JakobJenkov
2 жыл бұрын
You are very welcome :-)
@ankuraagarwal
4 жыл бұрын
Good one, quite helpful. Thanks Jakob.
@JakobJenkov
4 жыл бұрын
You are welcome :-)
@justinf1343
3 жыл бұрын
Great explanation of the Java Memory Model, you will already know this but volatile alone cannot be used for CAS related operations. I agree that volatile ensures all threads see the same value, but incrementing a variable can only be atomic via synchronization or by using an AtomicInteger
@JakobJenkov
3 жыл бұрын
Yes, I know that, and I cover that in several of my videos :-) There is one situation where it can work to increment a volatile variable though: Single writer - Single / multiple reader cases. If only one thread every writes to the volatile variable, then incrementing it is safe, or using it in compare-and-swap-like situations. If only one thread writes to a volatile variable, then only that thread depends on the variable's previous value, and no conflict occurs.
@justinf1343
3 жыл бұрын
@@JakobJenkov I’m not doubting that. I have seen far too many programmers who mark a shared variable volatile and when I say “that’s not thread safe” they try and argue it is because it’s volatile 😬
@anmolsandal3454
2 жыл бұрын
Great explanation 👌. Thank you for your work.
@JakobJenkov
2 жыл бұрын
You arr welcome :-)
@magdak1556
2 жыл бұрын
Perfect video. Thank you!
@JakobJenkov
2 жыл бұрын
You are welcome! :-)
@garimadhanania1853
4 ай бұрын
Awesome content, so clear!!
@JakobJenkov
4 ай бұрын
Thank you ! :-)
@ManishKumar-qx1kh
3 ай бұрын
Hi Jacob, Great explanation really appreciate and you just got a sub 🙂 Below are two points i need to ask:- 1) The main method itself runs in a thread so the threads defined are its local variables right? 2) You said object references are stored on stack and objects on heap but what if variable is a primitive type that is they are not objects.
@JakobJenkov
3 ай бұрын
Yes, the local variables in main() are local to the thread running main() Primitives don't have object references to them. The primitive values are store on the stack directly.
@gloriafigueroa8129
3 жыл бұрын
Thanks Jakob, these are some amazing videos!
@JakobJenkov
3 жыл бұрын
You are welcome! Glad you like them! :-)
@Ketrixx
3 жыл бұрын
Man that tutorial is amaizing !!!
@JakobJenkov
3 жыл бұрын
Thanks! Great to hear! :-)
@SoeaOu
3 жыл бұрын
this is mindblowing, love the vid, thanks
@JakobJenkov
3 жыл бұрын
Glad you liked it :-)
@andrewshatnyy
3 жыл бұрын
Amazing tutorial. Thank you for your work!
@JakobJenkov
3 жыл бұрын
Thanks - and you are welcome! :-)
@MrVipulLal
2 жыл бұрын
Good one, mate
@JakobJenkov
2 жыл бұрын
Thank you! :-)
@jovangrgur3266
3 ай бұрын
Great tutorial about multithreading and Java memory model, but one thing is missing. Diagrams are too static, when you explain different variants of code you should follow that and draw on diagram what is happening, because it will be more clearer. For example in section with local variables and object locations, for different combinations in code you are always using same diagram, so it is very confusing to realize what and which objects are created. This is just feedback from my side how to improve you tutorials
@JakobJenkov
3 ай бұрын
Thanks for the feedback ! I will try to think about that in future videos! :-) It's not always so easy to draw clearly the ideas I am trying to convey :-) But I will try to think more about it!
@jasper5016
2 жыл бұрын
You are really a fantastic teacher. Do you have any courses on Udemy or Pluralsight? You are a master of this topic. Can you please cover how can we write high transaction codes? Your tutorials are fun to watch and a lot to learn.
@JakobJenkov
2 жыл бұрын
Hi Jasper, I am glad my tutorials are helpful for you! :-) ... I don't have any courses on Udemy, Pluralsight, LinkedIn Learning ... only KZitem and Odysee, and my website jenkov.com so far :-)
@jasper5016
6 ай бұрын
@@JakobJenkov Thanks!
@ohadlevy5719
3 жыл бұрын
Thank you very much for the videos. they make the subject easy to understand. Keep it up and once again thank you :).
@JakobJenkov
3 жыл бұрын
Thank you for your feedback! ... I have many more videos planned - it's mostly a question of getting the time to record them :-)
@marmont8005
8 ай бұрын
Thank you, bro Nice work!
@JakobJenkov
7 ай бұрын
Thanks - and you are welcome ;-)
@Shonia
2 жыл бұрын
Wonderful tutorials! Thank you a lot!
@JakobJenkov
2 жыл бұрын
You're very welcome! :-)
@billwu7367
Жыл бұрын
So professional!respect!
@JakobJenkov
Жыл бұрын
Thank you 😊
@vikrantkaushal9650
4 жыл бұрын
Thanks, your videos are awesome. Can you please comment that why both threads didn't stop at one million even after using synchronized block? IMO they should have because as log as one thread hit million, it should come out of for loop?
@JakobJenkov
4 жыл бұрын
Both threads loop for 1 million times in total. The for-loops do not look at the "count" variable to determine how many times to loop. They only look at their own "i" variables. That means, that the threads will both loop 1 million times, and in total that should result in 2 million loop iterations. The threads only share the "count" variable - not their "i" variables.
@vikrantkaushal9650
4 жыл бұрын
@@JakobJenkov oops my bad. Hats off sir. Your videos are really good. Thanks a lot
@srinivastadinada4846
3 жыл бұрын
Hidden gem..
@JakobJenkov
3 жыл бұрын
Thanks :-)
@osamabassam7517
3 жыл бұрын
Amazing explanation.
@JakobJenkov
3 жыл бұрын
Thanks :-)
@qwlol
3 жыл бұрын
I wish I could give you more likes
@JakobJenkov
3 жыл бұрын
:-D ... well, I appreciate every like my videos get - even if just one at a time ;-)
@lbirowka
3 жыл бұрын
Excellent explanation. Could you share with us images of those diagrams?
@jgwhite5728
3 жыл бұрын
Awesome tutorials!
@JakobJenkov
3 жыл бұрын
Thank you very much !!! 😊
@AbhishekVaid
2 жыл бұрын
My biggest confusion is that if threads are also java objects, they would also be instantiated on heap. Moreoever, if two threads share an object and that object has state, then if both threads update that state (through setters on the shared object) then would each thread make a copy of that state in their register? Would it mean we have two copies of that state in two CPU registers, simply because we exposed that state (which is still very much part of only 1 object on heap) to two threads ?
@JakobJenkov
2 жыл бұрын
Yes, each thread *may* hold a copy of the state of a shared object in different CPU registers at the same time. That is why we use volatile variables or synchronized blocks - which both force reads of a variable to come directly from main memory and writes to go back to main memory.
@bayraminanc885
3 жыл бұрын
perfect explanation
@JakobJenkov
3 жыл бұрын
Thank you :-)
@trdngy8230
4 жыл бұрын
Thanks for your work!
@JakobJenkov
3 жыл бұрын
My pleasure! :-)
@abenezertilahun610
3 жыл бұрын
Thank you
@JakobJenkov
3 жыл бұрын
Welcome!
@Anonimus_13
2 жыл бұрын
nice tutorial, thank you) Have just one question, is synchronized keyword enough to guarantee atomicity ? Don't we need to use volatile keyword as well to guarantee that the operations are performed directly via RAM?
@JakobJenkov
2 жыл бұрын
If you use a synchronized block you do not need to use the volatile keyword around the variables accessed inside the synchronized blocks. The volatile keyword is used to provide some level of thread visibility without having to use synchronized blocks. Thus, volatile is a weaker thread synchronization mechanism, but it offers higher performance than synchronized blocks - e.g. via non-blocking concurrent algorithms and data structures.
@123iamnoob
2 жыл бұрын
Nice tutorial! I have two questions, if you don't mind. One thing that is puzzling is that in the last example even though we used synchronized one thread got the count of 2 million (expected) but the other one did not? How's that possible? The other question would be, if we were to use class that "extends thread" instead of implements runnable to recreate the scenario, and we had a member field that is a reference type (for example Count count) in that class, where would that member field "live"? We created two thread stacks, but I'm not sure if "count" referencing variable would be located on thread stack since it is not "local variable" but rather member field. Where are member fields located that's sort of the main question. Hopefully my questions help others with same dilemmas :)
@JakobJenkov
2 жыл бұрын
One thread will finish counting to 1 million before the other thread. Only one of the threads can add the last 1 to turn the total count to 2 million (2 x 1 million). A member in a Thread subclass would live within instances of that Thread subclass. Thus, each thread would end up having its own count field. Member fields are stored on the heap within with the object.
@jericho7989
2 жыл бұрын
well explained 👏
@JakobJenkov
2 жыл бұрын
Thank you :-)
@khomo12
2 жыл бұрын
Great!
@JakobJenkov
2 жыл бұрын
Thanks! :-)
@nopepsineedcola8893
3 жыл бұрын
so good
@JakobJenkov
3 жыл бұрын
Thanks :-)
@RobbieBobbie107
3 жыл бұрын
this is a great video thank you
@JakobJenkov
3 жыл бұрын
You are welcome! Glad you liked it! :-)
@a.yashwanth
4 жыл бұрын
21:23 why the count is different for both threads? If the count is shared between threads they should print same values right?
@JakobJenkov
4 жыл бұрын
I cover that in the video. If two threads share a member variable, and that member variable is not declared volatile, nor accessed from inside a synchronized block, there is no guarantee about when each thread will read the latest value of that variable from main memory into CPU registers, nor any guarantees about when each thread will commit the latest value of the member variable back to main memory so other threads can see it. Thus, each thread may be working on "stale" local values - not seeing the changes other threads have made to the same member variable. In the case of a shared count variable which is read-then-incremented, declaring the variable volatile is not enough - because a read-check-change-write operation on the same, shared variable by multiple threads will lead to race conditions. Thus, the read-check-change-write operation must be "atomic" - which can be achieved by performing these operations within a synchronized block (or using e.g. an Atomiclong as counter etc.).
@a.yashwanth
4 жыл бұрын
@@JakobJenkov I got it now. The reason why I asked it because I thought both threads exit at the same time.(you didn't mention this in the video). And as they have access to same variable location in memory they should print same value when both exit at same time.(even though count is different due to race condition) So according to your explanation I understood that there is no guarantee that threads exit at same time.
@michaelhughes8413
3 жыл бұрын
@@a.yashwanth I think *any* use of the count must use synchronized (or volatile) in order to get the right value. In the code example, the increment to 'count' is synchronized. The System.out is not synchronized, so i presume it uses a value from the Register or Caches?
@Qladstone
3 жыл бұрын
@@michaelhughes8413 The thread that finishes incrementing first will have incremented the count by a million. At this point the count may not be 2 million yet and it may proceed to create the string that is to be printed out with this < 2 million count. Suppose this evaluation is done, but the scheduler decides to delay the System.out.print I/O call and let the other thread complete the rest of its task. Then you have the other thread incrementing the count to 2 million, creating the string, then printing it out. And finally the first thread prints out the string that now contains the old value of the count. Even if you synchornized the System.out portion, the thread that finishes first can still print a < 2 million count. The only guarantee is that it will print this < 2 million count before the other thread prints the 2 million count.
@timurkhasanov5978
3 жыл бұрын
thanks!
@JakobJenkov
3 жыл бұрын
Welcome! :-)
@kamilemirov9479
2 жыл бұрын
I didn't understand why Thread 2 printed 1674273 at 22:23 ? I expected them to print 2 million since access to count happening inside the synchronized block
@JakobJenkov
2 жыл бұрын
Only the second thread will see the full count of 2 million. The two threads each increment the counter 1 million times and print the value of the counter at the time they finish incrementing 1 million times. Thus, the first thread has finished incrementing 1 million times when the total count is 1,674,273 . At that time the second thread has only incremented the counter 674,273 times.
@hliebhalunko5214
2 жыл бұрын
@@JakobJenkov doesn't that mean that "Thread 2 : 1674273" should be printed first as Thread 2 finished first?
@giantbush4258
7 ай бұрын
Imagine each thread dropping a pebble into a shared bucket for each iteration. And each thread will use the total bucket count before incrementing. In the best case one thread will be 1,999,999 and the other one 2,000,000. Because one thread will finish before the other one.
@marcin83kra
Жыл бұрын
Jakob, how can you explain that if we set the counter variable as volatile, both results are usually less than 1 000 000.
@JakobJenkov
Жыл бұрын
Even if a shared counter is volatile - the increment operation (counter++) is not atomic. The incrementation does not happen out in the memory where the volatile memory is stored. Two CPUs might load the value of the counter into a CPU register, increment it, and write that value back to the volatile variable. If both CPUs load the value 2 into a local CPU register, both will increment it to 3, and write 3 back to the memory. Even if both variables write the incremented value back to memory immediately, one of the increments will "get lost". Only writes to a volatile variable are atomic. But - an increment is a read-increment-write operation - and is thus not atomic. This is, by the way, what we have atomic operations such as compare-and-swap for. I've made a vide about that too, here: kzitem.info/news/bejne/1pyNvH9tfHqAdKA
@woosukbyun2455
Жыл бұрын
Thank you so much for the quality video! I just have one question. I recently tried hard to really grasp what the word jvm stands for. But, the word jvm is explained quite differently at different places. Watching your video, it seems like jvm is just a part of physical ram. Am I correct on this?
@JakobJenkov
Жыл бұрын
JVM meand Java Virtual Machine. It is the application (process) that executes your Java application.
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