Singleton Pattern - Design Patterns (ep 6)
Vložit
- čas přidán 26. 06. 2024
- Video series on Design Patterns for Object Oriented Languages. This time we look at the Singleton Pattern.
► The playlist
• Design Patterns in Obj...
► Head First: Design Patterns
geni.us/nlbA6
► Design Patterns: Elements of Reusable Object-Oriented Software
geni.us/PsXmo
► Clean Code Talks at Google, by Miško Hevery
• "The Clean Code Talks ...
• "The Clean Code Talks ...
• The Clean Code Talks -...
• The Clean Code Talks -...
• How to Write Clean, Te...
💪 Patreon Community
/ christopherokhravi
📚 Products I Recommend
geni.us/71ZXF
Boss: My wife is cheating on me
Programmer: One man's constant is another man's variable....
🤣🤣
'The Variable Man' - by Philip K. Dick
Is this lose?
once a variable, always a variable :D
@@bazejtez6635 Unless you garbage collected :D
Me: Let me learn about Singleton pattern.
Christopher: never use singleton pattern.
Me: -_-
You can use it tho. In Typescript Nestjs Framework alsmost every class is a singleton and its fine.
You should never use it, except when you should. (eg. it is good to prevent database connection leaks)
@@eugeneganshin2934 so like redux store is a singleton in a javascript/react world ?
One of the best series I have ever watched. Keep going on dude!
mohammad naseri thank you for the kind words. I'm glad it's useful :)
Love these videos, thanks Christopher! The Head First series is great.
Karl Hadwen thanks! I'm very glad they're useful. Thanks for watching :)
Your editing is absolutely fantastic. The stream of knowledge never stops or slows down.
Everything makes sense with that kind of explanation! Thanks, Chris!
Thank you for the very kind words. Much appreciated and I'm glad to hear it. Thanks for watching :)
This is why I love the internet, good videos with good info. My man!
If there is anything comparable to your teaching skills, it's your skills to have amazing intros. Intro for this particular video is simply genius. Your intros are so underrated man!
“One man’s constant is another man’s variable”... Woow!!
That's a good video. Especially the code smell part. I would add though that to ensure single instance you also need to wrap instance creation with lock (Monitor), because nowadays threads are used left and right. In fact, "double-checked locking" (that's a pattern) should be used
if (instance == null) {
lock (_lockObject) {
if (instance == null) {
instance = new Singleton();
}
}
}
Sorry for asking such a newb question but what is purpose of locking here.
@@GohersWay Locking prevents execution of the enclosed code by multiple threads. We want "instance = new Singleton()" execute only ONCE in entire process lifetime and for that we need to make sure that inner "if (instance == null)" is never evaluated SIMULTANEOUSLY (but theoretically it can happen more than once, if two threads happen to access the singleton instance for the FIRST time simultaneously). Now, why do we need outer "if (instance == null)" - because it's much cheaper than lock in terms of CPU. If a web application runs for 30 minutes before process recycling, then 99.9% of instance access cases by different threads will go no further than outer if, 0.09% will create monitor, wait on that monitor, and evaluate inner if, and 0.01% will actually execute inner if's enclosed code (instance = new Singleton).
@@mikhailbisserov8017 but even if two threads access that part of creating the object, why should it be a concern ? considering, first instantiation call is just necessary (but state will always be random, so hardly matters who creates it finally or been changed by some other threds at same time)
@@good_life_videos if two threads create instances of the object, it's not Singleton by definition. WHY we want to create it only once is an out-of-scope question. It's a given task, purpose of Singeton. Usually it's for performance and memory conservation, maybe even acquiring lock to some unique underlying resource, but again, it's out of scope.
this guy and explanation is pure gem
That's what I call 'in-depth explanation'! Awesome work.
U, my good Sir are born for teaching, really nice and simple explanation for everyone to understand. Keep up the good job!
cheers
The way you teach these lessons is perfect. This is a good example for my lecturers how to teach these stuff.
The Clean Code links are all great! Now, back to your videos! I wound up learning as much from this as any of your others in this playlist, thanks to the excellent links provided in the description. Singletons seem very convenient, until test-time...
Already learned this in university and now planning to review again, my professor who teaches that course is very good, and your lecture is as good as the course I learned before ! Thank you so much ! Waiting for more
You are criminally underrated. Deserves more followers. Top notch.
Singleton design pattern is simple, however, complicated! every line of the code was explained thoroughly and beautifully.. well done! One of the best videos ever for Singleton!
You are one of the best teachers on the planet. Thanks for the videos.
This series is greatest I've ever encountered on youtube on any topic, period.
Same here
The way you teach is fantastic, you are my inspiration.
Thank you for this video and all the rest. I really hope to find every single Design pattern explained by you in this play list.
The best playlist (on IT/Sw) I have ever watched on CZcams
A clear video on single ton design pattern. Thank you.
Your explanation is clear and precise. I enjoyed the video and was able to understand the nuances of this pattern very well.
I love how you explained this. Very clear. 👏
This is the best explanation of a Singleton pattern ever !!
don't understand why this video is not popular than it has to be. You are amazingly well explaining abstract concepts so dumb like me can understand. Thanks.
I love the way you teach. Your explanations are thorough and the way you speak is very captivating. Straight to the point, you are not a time waster.
Very informative! Thank you very much for this fantastic explanation, and for presenting it in such a good-natured way!
The best explanation of Singleton pattern i have come across
Simplest and clear explanation I've come across. Thanks
These videos are so precious thank you!
NIce man, totally grasped for the first time, thank you so much.
Super clear! Thanks Christopher!
Thanks, your explanation was clear and convincing :)
Dominik Roszkowski thanks for sharing and for watching :)
Gooooooooood one !!!! Very clear ! Clear all my concepts !
This is quality man. Keep the good work, youtube definitly needs that. Well done
+JohnyJohn Johny Thanks! And thanks for watching :)
First time seeing your videos... I give a 10000 likes for your cuts and edits. Your videos are full of info (no lags and time waste). That itself proves you value your trade.. Kudos
Thank you for making this series ❤❤❤
It was really helpful that you went through the code in this video; great series! :)
You're views must really go up every December/January. Exams time and your explanations are great, thanks man
i got a UML exam tomorrow , and i've been watching your video , your videos are saving my life right now
Just wanted to let you know that you are amazing for making this series!
Thank you. You peeps are amazing for watching it :D
As much as we try to avoid Singletons, we do run into scenarios where we have to use one. Specially when working with native Android using Java where for creating Fragments, we use a public Instance property to get access to it. These Instances are then held in memory for various operations done by the OS.
Great series, keep it up :)
god bless you, christopher. Please keep making videos!!
This is perfect. Thank you so much.
Fantastic series. When I get my first dev job I will do what I can to support you.
Clear, audible video. Keep it up
Super awesome mate. Clear explanation.
you have really simplified design patterns ... classic explaination ... thank you very much
+Glenn Dsilva Thanks for letting me know! :) And thanks for watching!
Thank's for all the Knowledge🤜
Hey SIr , I am Sri Lankan IT Undergraduate , you do explain these design patterns very well and Thank You So much. It was really helpful me to figure out the answers for the design patterns questions in our university :)
The way you jump entered, I expect to hear "Hey Vsauce" :P . Awesome video.
BEST VIDEO EVER!!!!! So much better than university lectures
Brilliant work - thank-you.
great video. finally I found explanation in a style that I can understand clearly. Thanks for the lesson. I am now a subscriber.
+AVBFANS Awesome! Welcome to the channel :) And thank you for sharing your thoughts :)
Thanks a lot! Very cool vivid explanations and examples! Thanks! Thanks! Thanks!
Your explanation of concepts are easy to understand 👏👏👏👏👏
Oh my god, you are a good explainer! I'm actually understanding what's happening
very good explanation of Singleton. Thanks Christopher
I have watched all your videos on Design Pattern, You rock!!! keep up the good work. :)
SNHU is using this video as material reference. you should feel proud that an university is using your videos to teach new students :)
Liked the way you describe different aspects of decision making and assumptions related to pattern
Clearly explained ! thank you .
this amazingly amazing , thankyou brother.
That was great! thank you 🙌
Thank you for your videos !
such a wonderful lecture . concept clear now.
Thanks Christopher! I will definitely check out those links. On to the next pattern :)
Hitesh Rana cool! They're worth the time. Misko seems like a very smart guy. Thanks for watching!
Explained the matter nicely.
thanks chrostoper the best video about singleton i ever watched
Thanks Christopher really your explanation is very good
Very nice and detailed explanation of design pattern concepts.... I am waiting for other remaining design patterns videos ..... Thank you very much.
Not sure about other languages, but in C++, the preferred approach to singletons is known as the Meyers Singleton (named after Scott Meyers who included it in his book Effective C++). The idea is to declare the variable within a method rather than as a member variable. This is thread safe, and it also allows you to skip the check to see whether or not the singleton exists. The code looks like this:
class Singleton {
private:
Singleton() {}
public:
static Singleton& getInstance() {
static Singleton instance;
return instance;
}
};
I don't think intra-method static variable magic exists in non C languages, I think it's mostly a C thing. By the way, I'm assuming you meant static Singleton instance = new Singleton()
@@yoavmor9002 It's not a pointer, so they did not mean that.
thanks again Christopher. your videos are great
Lav Gupta thanks! And thanks for keeping up the watching :)
Excellent. easy to understand. Thank you.
One of the best video series I have ever seen. Superb explanation. Quite like the way you do these videos in your own style. Keep up the good work.
P.s. loved ur writing and honesty :P
Thanks! I'm glad to hear that the style works :) Thank you for the encouragement and for watching the series :)
watching keenly!
tivmego :D
had to add - you are amazing! great vids once again Thank you.
You are a great instructor. Keep it up please.
Woooow, Thanks christopher for this wonderful series. Your teaching style is awesome. waiting for other design patterns :)
+Irshad ck Thank you. Makes me glad to hear. Next one is coming very soon. Thanks for watching :)
really awesome explanation
Explained well thanks buddy 😊
Great video! However, the argument is not that Singletons are necessarily bad except that they are misunderstood, often abused and can introduce unwanted side effects when used without proper thought -- a lot of frameworks use Singletons :D.
For instance, I have this piece of (framework) code that manages all of my configurations (and of subsystems) and the construction of this object is really heavy and doesn't even lend itself to a prototype or flyweight. It is important that these bits of configuration happen only once at application startup. Instead, I hide my singleton configuration instance behind an abstraction and delegate the construction and life cycle to a DI / IOC container. In other words, users only have to depend on that abstraction e.g. IConfigurationManager etc.
In addition, the one thing (or two) I think you're missing is the issue of potential race conditions or thread-safety in concurrent systems when handling stuff like this manually -- why it's important to use a good DI framework and instead depend on abstractions. Plus, it is your responsibility to ensure that your object is IMMUTABLE upon construction and member access is read-only.
Thank you! Good points.
The only time I have used a Singleton is when I was developing my own small website, wanted a quick cache, and only needed to load the database once at application startup to save on Cloud Database DTU hits. The webpage did load faster using the Singleton as a cache. A static class also worked for this scenario and is a little more straightforward. Either was ok for this scenario because I only changed the data about once per month, could restart the application when I wanted, and didn't have sessioned users on the site yet.
However, once I want to add/change data in the database and want to reset the cache without an app restart, it is a dead-end; so it is not practical for many business production scenarios.
I was just looking at 5-6 ways to cache and those were the quickest but most limited.
Singleton can be used in notification servers for mobile devices or others, when you always have one and only one instance to call to add or remove observers. :) thx Christopher Okhravi for clearing this out!
Great Series...Thanks for making those video ... waiting for more videos.
Dude I really love your videos! Keep up the great work :)
Excellent i have a java architecture certificate exam within 3 months. You made me clear with the design pattern. Many thanks. Bless you
+gokhan tuncel I'm glad to hear. Thank you very much for sharing and best of luck on the exam :)
I love Singleton in Unity. Very handy for Manager objects.
It could become your worse nightmare xD
@@TheLucausi I've actually seen it unfold before me when the project I am working on became large. The Manager became this class with lots of states. Singleton, despite being great for Manager objects, should still be used sparingly :D
if one is a religious fanatic and assembles a God class, singleton pattern seems like an obvious choice :)
+Radek P This comment is quite simply hilarious :D :D
Radek P LOL!!! For Indian Hindu fanatic it's probably a fly weight pattern with millions of fly weights
Unless you have more than one god, then you have to refactor the whole universe.
have you ever heard about Polytheism?
don't you mean polymorphism? ;-)
Love u sir, U make design pattern so easy
Excellent explanation Cristopher! Only one thing to note: what happens in a multi-threaded environment? It may happen that two different threads call the getInstance() method and because of this, more than one instance of the Singleton class is created. The only way to ensure a single instance is to add the synchronized in the getInstance method signature or (it would be better), synchronize the block of code in which we check if the instance is null (the if statement).
Congrats for your videos!
Superb man, you explained very well. I really got lot of interest on design patterns. Thank you so much I leant a lot from your video's.
It’s very helpful, thanks
Best explanation, thanks a lot
I was waiting for this one :) wow it's wonderful
avi fuel :D
Great Explanation!
Very good explanation.. really help for me..