Who Takes Out Your Trash?

A presentation at NodeFest in November 2018 in Tokyo, Japan by Sanne Kalkman

🔮 💻 Magic is just (computer) science you don’t understand yet

🧠 🔍 🗑 Allocate memory Find the garbage Free up memory

📚 🔥 Running out of memory Breaking things

REFERENCE COUNTING If nothing points to it, nothing’s using it

REFERENCE COUNTING name name = “nodefest” “nodefest” 1

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” 1

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” other_name 2

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” name = nil other_name 2

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” name = nil other_name 1

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” name = nil other_name = nil other_name 1

REFERENCE COUNTING name name = “nodefest” other_name = name “nodefest” name = nil other_name = nil other_name 0

CYCLES a = { other: nil } a { other: nil } 1

CYCLES a = { other: nil } b = { other: a } a { other: nil } 1

CYCLES a = { other: nil } a { other: nil } 1 b { other: a } 1 b = { other: a }

CYCLES a = { other: nil } a { other: nil } 2 b { other: a } 1 b = { other: a }

CYCLES a = { other: nil } a { other: nil } 2 b { other: a } 1 b = { other: a } a[:other] = b

CYCLES a = { other: nil } a { other: b } 2 b { other: a } 1 b = { other: a } a[:other] = b

CYCLES a = { other: nil } a { other: b } 2 b { other: a } 2 b = { other: a } a[:other] = b

CYCLES a = { other: nil } a { other: b } 2 b { other: a } 2 b = { other: a } a[:other] = b a = nil b = nil

CYCLES a = { other: nil } a { other: b } 1 b { other: a } 2 b = { other: a } a[:other] = b a = nil b = nil

CYCLES a = { other: nil } a { other: b } 1 b { other: a } 1 b = { other: a } a[:other] = b a = nil b = nil

MARK & SWEEP If you can’t get to it, you can’t be using it

COPYING COLLECTION Keep your stuff together

COPYING COLLECTION 0 1 0 2 2 3 4 5 6 7 8

COPYING COLLECTION 0 1 2 0 2 3 3 4 5 6 7 8

COPYING COLLECTION 0 1 2 3 0 2 3 4 4 5 6 7 8

COPYING COLLECTION 0 1 2 3 4 0 2 3 4 5 5 6 7 8

COPYING COLLECTION 0 1 2 3 4 5 0 2 3 4 5 7 6 7 8

COPYING COLLECTION 0 0 2 2 3 4 5 3 4 5 7 7

GENERATIONAL COLLECTION If you’ve been using it for a while, it’s probably important

GENERATIONAL COLLECTION New objects Old objects D

🔮 💻 Garbage collection is no longer magic!

LET ME KNOW WHAT YOU THINK! Tweet me @sannekalkman Find me in person later! The Garbage Collection Handbook - Jones, Hoskin & Moss

Sanne Kalkman
@sannekalkman

1 / 81

Even clean code creates garbage. Although most of us don't take out our own trash, we should still know how it's done!

In our daily development lives, most of us don’t have to worry about unused objects gathering cobwebs and filling up the memory. All we need to know is that our language has a garbage collector that just comes by and makes our trash disappear. Somehow it figures out what should stay and what can go, our program can keep going without running out of space, and we don’t have to do a thing.

It is not in fact magic that takes care of the garbage, and this talk will show you how it’s done. First, we’ll explore how two of the most common garbage collection algorithms, reference counting and tracing, figure out what is ready to be collected. Next, we’ll see how we could get the garbage truck out of the way faster by using a generational algorithm,

This friendly introduction to taking out the trash gives an overview of important aspects of garbage collection algorithms. It is specifically meant to be accessible developers of all levels and you’ll walk away with an understanding of and appreciation for all the hard work that goes on behind the scenes.

Resources

The following resources were mentioned during the presentation or are useful additional information.

Garbage Collection Handbook

Very extensive book on garbage collection, for if you want to know more!

Who Takes Out Your Trash?

Link for this presentation:

HTML code for embedding:

Share on social media:

Resources

Garbage Collection Handbook