Who Takes Out Your Trash?

WHO TAKES OUT YOUR TRASH? @sannekalkman

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🔮 💻

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

🧠 Allocate memory

🧠 🔍 Allocate memory Find the garbage

🧠 🔍 🗑 Allocate memory Find the garbage Free up memory

📚 Running out of memory

📚 🔥 Running out of memory Breaking things

DANGLING POINTERS

DANGLING POINTERS 🔥

DANGLING POINTERS 🔥 Memory Leak

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

REFERENCE COUNTING

REFERENCE COUNTING name = “codeBEAM”

REFERENCE COUNTING name name = “codeBEAM” “codeBEAM” 1

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

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

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

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

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

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

CYCLES

CYCLES a = { other: nil }

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

MARK & SWEEP

COPYING COLLECTION Keep your stuff together

COPYING COLLECTION FROM Space TO Space 0 1 2 3 4 5 6 7 8

COPYING COLLECTION FROM Space 0 TO Space 0 1 2 3 4 5 6 7 8

COPYING COLLECTION FROM Space 0 1 TO Space 0 2 2 3 4 5 6 7 8

COPYING COLLECTION FROM Space 0 1 2 TO Space 0 2 3 3 4 5 6 7 8

COPYING COLLECTION FROM Space 0 1 2 3 TO Space 0 2 3 4 4 5 6 7 8

COPYING COLLECTION FROM Space 0 1 2 3 4 TO Space 0 2 3 4 5 5 6 7 8

COPYING COLLECTION FROM Space 0 1 2 3 4 5 TO Space 0 2 3 4 5 7 6 7 8

COPYING COLLECTION FROM Space 0 TO Space 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

WHAT ABOUT THE BEAM? Erlang & Elixir garbage collection

📬 Processes

📬 🚫 Processes Immutability

MEMORY LAYOUT Shared

MEMORY LAYOUT Process A A Shared

MEMORY LAYOUT Process B Process A A B Shared

MEMORY LAYOUT Process B Process A A B Process C C Shared

MEMORY LAYOUT Process B B Process C C Shared

MEMORY LAYOUT Process B Process D D B Process C C Shared

PROCESS MEMORY Heap Stack

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space 1 2 3 4 5 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space 1 6 2 3 4 5 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space 1 6 2 3 4 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space 1 2 6 1 3 4 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 6 1 3 4 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 3 6 1 5 4 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 3 6 1 5 4 M 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 3 4 6 1 5 3 M 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 M 3 4 6 1 5 3 M 5 M 6 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space M 1 2 M 3 4 6 1 5 3 M 5 M 6 7 8 9 7 8 9

COPYING COLLECTION ROOTS 4 1 3 6 2 5 FROM Space TO Space 6 1 5 3 7 8 9

GENERATIONAL COLLECTION FROM Space TO Space OLD Space 6 3 5 1 8 9 8 9

GENERATIONAL COLLECTION High-water mark FROM Space TO Space OLD Space 6 3 5 1 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space TO Space OLD Space 6 3 5 1 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space TO Space OLD Space 6 3 5 1 A 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space TO Space OLD Space 6 3 5 1 A B 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space TO Space OLD Space 6 3 5 1 A B C 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space 6 TO Space OLD Space 5 3 M 5 1 A B C 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space 6 TO Space A OLD Space 5 3 M 5 1 M A B C 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space 6 3 TO Space A C OLD Space 5 M 5 1 M A B M C 8 9 8 9

GENERATIONAL COLLECTION * High-water mark FROM Space 6 M 3 TO Space A C OLD Space 5 3 M 5 1 M A B M C 8 9 8 9

BINARY HEAP

BINARY HEAP ✉ Binaries > 64 bytes

BINARY HEAP ✉ 🔢 Binaries > 64 bytes Reference counted

🔮 💻 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 Erlang Garbage Collector - Lukas Larsson (Erlang Solutions)