Who Takes Out Your Trash?

A presentation at CodeBEAM Lite Amsterdam in November 2018 in Amsterdam, Netherlands by Sanne Kalkman

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WHO TAKES OUT YOUR TRASH? @sannekalkman

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🔮

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🔮 💻

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

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🧠 Allocate memory

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🧠 🔍 Allocate memory Find the garbage

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🧠 🔍 🗑 Allocate memory Find the garbage Free up memory

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📚 Running out of memory

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📚 🔥 Running out of memory Breaking things

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DANGLING POINTERS

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DANGLING POINTERS

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DANGLING POINTERS 🔥

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DANGLING POINTERS 🔥 Memory Leak

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

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REFERENCE COUNTING

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REFERENCE COUNTING name = “codeBEAM”

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

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

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

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

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

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

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

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

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CYCLES

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CYCLES a = { other: nil }

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

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

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

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

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

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

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

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

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

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

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

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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MARK & SWEEP

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COPYING COLLECTION Keep your stuff together

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

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

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

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

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

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

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

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COPYING COLLECTION FROM Space 0 TO Space 0 2 2 3 4 5 3 4 5 7 7

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COPYING COLLECTION FROM Space 0 TO Space 0 2 2 3 4 5 3 4 5 7 7

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

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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GENERATIONAL COLLECTION New objects Old objects D

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WHAT ABOUT THE BEAM? Erlang & Elixir garbage collection

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📬 Processes

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📬 🚫 Processes Immutability

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MEMORY LAYOUT Shared

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MEMORY LAYOUT Process A A Shared

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MEMORY LAYOUT Process B Process A A B Shared

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

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MEMORY LAYOUT Process B B Process C C Shared

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

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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PROCESS MEMORY Heap Stack

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

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

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

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

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

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

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

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

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

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

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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

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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

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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

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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

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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

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BINARY HEAP

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BINARY HEAP ✉ Binaries > 64 bytes

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BINARY HEAP ✉ 🔢 Binaries > 64 bytes Reference counted

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🔮 💻 Garbage collection is no longer magic!

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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)