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Hello.

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In this video, we'll talk about topic nine, what our generation's garbage collector has a lot of work.

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It needs to identify objects to be removed, which we learned about in the previous lecture.

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Then it must actually remove them.

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Finally, it must fragment the memory of the application.

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As we know, the garbage collector marks objects as writable or unreachable and removes the latter from

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their memory.

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Imagine there is some object.

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Let's call it object a during the first execution of the garbage collector.

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This object is marked as readable, and so are objects reachable from object a.

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After some time, the garbage collector gets to work again and again.

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It marks objects and its friends as switchable.

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Then again, sometimes buses and garbage collector gets triggered again.

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And one more time it marks objects as reachable.

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If I were the garbage collector, I would probably get a bit frustrated.

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This object is obviously a long grift, and I don't want to check if it's still needed every time I

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get to work.

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I have other things to do.

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Well, that's exactly the optimization.

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The garbage collector creators come up with to not make it check each object every time.

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If some object survived a couple of cycles of the garbage collectors work, it's most likely a long-lived,

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and we should check it only every once in a while.

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This optimization introduced the concept of generations of objects.

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Once an object is first created, it is assigned to Generation Zero if it survives its first collection.

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It advances to generation one if it survives the second.

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Its advances to generation to the garbage collector checks objects from generation zero most frequently

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less frequently, its tookes objects from generation one and the least frequently from generation two.

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It makes sense if the object survived two collections.

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It's most likely long lived and there is a big chance it will survive collections number 10, 20 or

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100.

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We don't need to check that often.

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For example, think of some larger objects.

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Often there is one object created at the start of the program execution, and it is passed around to

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other crafts that needs it.

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Its lifecycle is basically as long as the time the application runs as the opposite.

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We often create objects that lasts only for a very short time, like aligning with objects created to

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carry some data between link quarries.

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In this case, it is reasonable that the garbage collector will quickly remove them so they don't occupy

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memory for too long.

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In a world tuned application, most objects die in generation zero.

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Please note that during a collection of a generation, all previous generations are also corrected,

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so one generation zero is collected.

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No other one is, but one generation two is collected.

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Generation zero and one are two.

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And that's why collecting objects from generation two is sometimes called a full garbage collection.

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One more thing that needs to be mentioned is the large objects heap when a very large object so larger

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than 85 thousands of birds is initially created.

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It is stored in a special area of memory called the large objects heap, and it is assigned to generation

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two right away.

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It gets this special treatment because it really happens that very large objects are short lived.

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Also, the objects in the large objects heap have one more special feature.

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They are pinned.

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It means they were meant to be moved in memory.

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During that, the fragmentation step of the garbage collectors work what happens after removing and

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reference objects from memory?

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This is because the larger object is the more expensive is the operation of moving it, and the harder

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it is to find the chunk of memory large enough to fit it.

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It's better to pin such large objects and move smaller objects around them.

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Let's summarize the garbage collector device objects into three generations zero, one and two.

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Depending on their longevity.

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Short lived objects belong to generation zero, and if they survived their first correction, they are

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moved to generation one and after duct to generation to the garbage collector collects objects from

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generation zero most often and from generation to earliest often.

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This feature is introduced in order to improve garbage collector.

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Performance objects that survived a couple of cycles of the garbage collectors work tend to be long

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lived and they don't need to be looked upon so often.

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This way, the garbage collector has less work to do, so it can do it faster.

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During the interview, you might be asked What is the large objects?

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Heap is the special area of the heap reserved for objects larger than 85000 bites.

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Such objects logically belong to generation two from the very beginning of their existence and are pinched.

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So what does it mean that the object is pinned?

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It means it will not be moved during the memory, the fragmentation that the garbage collector is executing.

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It is an optimization.

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Ask what objects are expensive to move, and it's hard to find a chunk of memory large enough for them.

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All right, that's it for this lecture.

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Thanks for watching, and I'll see you in the next one.