Awesome.....Haven't seen this indepth singleton implementation, mostly people just do a first level of implementation without thinking of the multithreaded environment.
Cool video! It would be dope if you could also explain an alternative approach of making a singleton using enums please. Oh, and numbering the videos would be really beginner-friendly and much appreciated by the viewers!
Not sure why you don't have much more views for this video. I don't think anyone explained the multi thread issue in any of the singleton pattern video. Great job and thank you.
I just found out about this channel and subscribed to it. Great Job! Although I think your volatile explanation is a bit wrong. I think volatile tells the OS that this variable will always be written/read to/from the RAM instead of the CPU cache memory. So let's dive in the example where we don't have volatile: Thread A enters the synchronized block and checks if instance is null (still haven't started initialization), at the same time thread B checks if instance is null outside the synchronized block and sees the instance to be null. Therefore thread B also tries to enter the synchronized block but will have to wait for thread A. Thread A after a successful initialization will exit the synchronized block and eventually return. But thread B on the other hand, inside the synchronized block will again see the instance to be null (since the instance variable might only be stored in the cache of a different CPU core where thread A was operating, and where thread B can't see), and will initialize it again. This will not be happening if the "instance" variable is declared volatile: Thread A enters the synchronized block and checks if instance is null (still haven't started initialization), at the same time thread B checks if instance is null outside the synchronized block and sees the instance to be null. Therefore thread B also tries to enter the synchronized block but will have to wait for thread A. Thread A after a successful initialization (will write instance to RAM directly instead of the CPU cache) will exit the synchronized block and eventually return. Now thread B, when checking again if the instance is null inside the synchronized block, will see that it is already initialized (since it will read directly from RAM) and will return that value. Correct me if I am wrong
Thank you for the support! I am afraid you are, it is exactly like I explained in the video, I suggest you watch that part again and if you still have trouble please let me know how can I improve my explanation in the future :) Additionally, feel free to check these references, maybe their approach will be better than mine at explaining the subject: stackoverflow.com/questions/11639746/what-is-the-point-of-making-the-singleton-instance-volatile-while-using-double-l (first answer in this Stack Overflow thread) or en.wikipedia.org/wiki/Double-checked_locking#Usage_in_Java (The part where they explain the "Broken multithreaded version"). Hope this helps! Cheers!
Good explanation , one question if some one calls clone method on the singleton instance , it will create another object right ? do we have to override clone method and return same instance , please explain ?
So with this pattern you can replace a single simple method that instanciate 10 different classes (implementing the same interface/abstract class) in a switch by 10 new creator classes to respect "Open to extension Close to modification" .... That's AMAZING ... What a great idea that's so much better now. LOL
What is the use of "private String data" field here? If i call the getInstance() function with some data string, it will not update the data field of the instance. The first getInstance() call will set the data value and it will never change again. What am I missing?
Nevermind, the question is already asked before and answered well. If anyone thought the same thing: A: Very nice! This video was mainly about the Singleton Pattern that is why I didn't want to delve other details. But what you could do is create a map and store several singletons based on their names, then the single instance would be tied to that name. So, in the most common example if you were using the singleton for DB instances and you were using two of them, you'll have two records in your map! Hope this helps :) Cheers!
After instance was initialised, it doesn't matter anymore what String data we pass as parameter to getInstance, it will always return the instance with the data when the method was called the first time. It this really the correct way of doing that?
Very nice! This video was mainly about the Singleton Pattern that is why I didn't want to delve other details. But what you could do is create a map and store several singletons based on their names, then the single instance would be tied to that name. So, in the most common example if you were using the singleton for DB instances and you were using two of them, you'll have two records in your map! Hope this helps :) Cheers!
Nope :) This is equivalent to result = new Singleton(data); instance = result; we need to assign the new Singleton created to the instance we have and not just the result being returned or else we will be fetching that result and creating a new instance every time! Cheers!
If the singleton needs to call a web service to fetch the singleton data such as access token, where do you place the logic to invoke the web service? Do you put it inside the singleton class or outside? Please clarify.
6:24 I don't get how volatile fixes the problem. It only makes thread B reread the variable from memory when returning it but the variable could still not be fully initialized by thread A.
No, it's just to check again if an instance is already created while the current thread was waiting for lock to acquire after the first check, 2nd check will be rarely used as most of times first check will be not null and return from there, double check is just for initialisation if many threads are trying to initialise the instance at the same time.
Very nice job. But we can still break this by serialize the object and deserialize it to create a duplicate object. I guess you should have covered that particular scenario on how to overcome that.
Damn man. That's a unique teaching ability to explain every reason. Nice.
Thanks a lot :) Glad it helped!
My left ear loved this
😂 Check our newest videos, we fixed that!
Awesome.....Haven't seen this indepth singleton implementation, mostly people just do a first level of implementation without thinking of the multithreaded environment.
Incredibly clear man THANKS
Good channel. I started reading Head First Design Pattern, but I think I'm gonna drop it and just learn from you.
Checking multiple references is not a bad idea, that's what I did when I try to put a video together! I am really glad you found our videos helpful :)
@@geekific Gonna watch them all.
Thanks for the video, it was really useful.
Great explaining skills, I read many documentation but I completely understood from your video
Awesome, thank you! Glad it was helpful :)
Very well constructed, step by step explanation. Thank you!
The only thing I have to say is 'Perfectly Awesome..........'. Thank you!
Cool video! It would be dope if you could also explain an alternative approach of making a singleton using enums please. Oh, and numbering the videos would be really beginner-friendly and much appreciated by the viewers!
Will add it to my list of upcoming videos! Stay Tuned!
Not sure why you don't have much more views for this video. I don't think anyone explained the multi thread issue in any of the singleton pattern video. Great job and thank you.
Thank you so much for a well coordinated video!! Kudos to you
My pleasure :) Glad you liked it!
Hey man, your videos are super awesome. Thank you so much for the good work
Thanks for clear explanation!
Thank you so much for making this video. Helped a lot!
overwhelmed
sick explanation and video
Thanks! Glad you liked it :)
Your videos are so so so good!! Thank You!!
That was giga clear.
Tanks buddy
I just found out about this channel and subscribed to it. Great Job!
Although I think your volatile explanation is a bit wrong.
I think volatile tells the OS that this variable will always be written/read to/from the RAM instead of the CPU cache memory.
So let's dive in the example where we don't have volatile:
Thread A enters the synchronized block and checks if instance is null (still haven't started initialization), at the same time thread B checks if instance is null outside the synchronized block and sees the instance to be null. Therefore thread B also tries to enter the synchronized block but will have to wait for thread A. Thread A after a successful initialization will exit the synchronized block and eventually return. But thread B on the other hand, inside the synchronized block will again see the instance to be null (since the instance variable might only be stored in the cache of a different CPU core where thread A was operating, and where thread B can't see), and will initialize it again.
This will not be happening if the "instance" variable is declared volatile:
Thread A enters the synchronized block and checks if instance is null (still haven't started initialization), at the same time thread B checks if instance is null outside the synchronized block and sees the instance to be null. Therefore thread B also tries to enter the synchronized block but will have to wait for thread A. Thread A after a successful initialization (will write instance to RAM directly instead of the CPU cache) will exit the synchronized block and eventually return. Now thread B, when checking again if the instance is null inside the synchronized block, will see that it is already initialized (since it will read directly from RAM) and will return that value.
Correct me if I am wrong
Thank you for the support! I am afraid you are, it is exactly like I explained in the video, I suggest you watch that part again and if you still have trouble please let me know how can I improve my explanation in the future :) Additionally, feel free to check these references, maybe their approach will be better than mine at explaining the subject: stackoverflow.com/questions/11639746/what-is-the-point-of-making-the-singleton-instance-volatile-while-using-double-l (first answer in this Stack Overflow thread) or en.wikipedia.org/wiki/Double-checked_locking#Usage_in_Java (The part where they explain the "Broken multithreaded version"). Hope this helps! Cheers!
Absolutely love the video although the last third of the video took 90% of my brainpower to keep up
Nicely explained. Thank you!
the best i've seen
Super clear 👏 Thank you !
You are amazing bro, you nailed it, I will definitely subscribe to such an amazing and valuable content channel, wish you growth and wealth :)
I appreciate that! Thanks for the support :)
Good explanation , one question if some one calls clone method on the singleton instance , it will create another object right ? do we have to override clone method and return same instance , please explain ?
That was a great explanation
thank you so much ,very clear
What's the music in the beginning?
Great video. But how to we actually use it now? Should there also be a setter to update the variables?
So with this pattern you can replace a single simple method that instanciate 10 different classes (implementing the same interface/abstract class) in a switch by 10 new creator classes to respect "Open to extension Close to modification" .... That's AMAZING ... What a great idea that's so much better now. LOL
Thank you!
Excellent
What is the use of "private String data" field here? If i call the getInstance() function with some data string, it will not update the data field of the instance. The first getInstance() call will set the data value and it will never change again. What am I missing?
Nevermind, the question is already asked before and answered well. If anyone thought the same thing:
A: Very nice! This video was mainly about the Singleton Pattern that is why I didn't want to delve other details. But what you could do is create a map and store several singletons based on their names, then the single instance would be tied to that name. So, in the most common example if you were using the singleton for DB instances and you were using two of them, you'll have two records in your map! Hope this helps :) Cheers!
Good channel. Helped me a lot. However I would request you to put even more detail to compete with other channels.
Happy it helped! and thanks for the feedback will take it into consideration in future videos :)
please explain eager and lazy instantion
After instance was initialised, it doesn't matter anymore what String data we pass as parameter to getInstance, it will always return the instance with the data when the method was called the first time. It this really the correct way of doing that?
Very nice! This video was mainly about the Singleton Pattern that is why I didn't want to delve other details. But what you could do is create a map and store several singletons based on their names, then the single instance would be tied to that name. So, in the most common example if you were using the singleton for DB instances and you were using two of them, you'll have two records in your map! Hope this helps :) Cheers!
That's exactly what I thought.
i want a written notes of what ever he said
can someone help me?
I think there is one mistake. An additional 'instance =' At the end it says instance = result = new Singleton(data);
Nope :) This is equivalent to result = new Singleton(data); instance = result; we need to assign the new Singleton created to the instance we have and not just the result being returned or else we will be fetching that result and creating a new instance every time! Cheers!
Oh, good to know. Thanks
If the singleton needs to call a web service to fetch the singleton data such as access token, where do you place the logic to invoke the web service? Do you put it inside the singleton class or outside? Please clarify.
Depends on what your singleton is. If that's its whole purpose, like a token generator or something then it should go inside.
OMG wow man
amazing!
Thank you :)
6:24 I don't get how volatile fixes the problem. It only makes thread B reread the variable from memory when returning it but the variable could still not be fully initialized by thread A.
It won't be there!
@@geekific I am afraid I don't understand what you are referring to, what won't be where?
It will not be written to memory until fully initialized
Good explanation, but the second if condition is redundant, isn't it?
Thank you! Basically more than half of the video was dedicated into answering this question. Kindly watch between 3:25 to 7:00. Cheers!
No, it's just to check again if an instance is already created while the current thread was waiting for lock to acquire after the first check, 2nd check will be rarely used as most of times first check will be not null and return from there, double check is just for initialisation if many threads are trying to initialise the instance at the same time.
good
>country can't have two presidents
San Marino has entered the chat
Very nice job. But we can still break this by serialize the object and deserialize it to create a duplicate object. I guess you should have covered that particular scenario on how to overcome that.
Thanks for the feedback! Will keep that in mind for future videos! Stay Tuned :)
There is so much stuff there. This feels like it should be solved by just making the whole thing a global atribute.
Cool, but you should use enum for that.
kichui bujhlam na
Please, let us know which parts exactly were not clear so we may try and help in the comments section :)
"most used pattern"
- As far as I know, many programmers call it an anti-pattern...
Being an anti-pattern isn't keeping people from using it ;P
That was giga clear.
Tanks buddy
Thank you!