Understanding Garbage Collection Through Visualizing a One Pass Real-Time Generational Mark-Sweep Garbage Collector!

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1. Understanding Garbage Collection Through Visualizing a One Pass Real- Time Generational Mark-Sweep Garbage Collector! Andrew Gwozdziewycz (Guh-shev-itz) http://apgwoz.com !!Con, 2014
2. Free the mallocs
3. Manual Memory Management is Difficult
4. Acquire. Process. Release.
5. Naive Mark-Sweep
6. Mark sweep: Roots management, marking Marked
7. Mark sweep: Sweep Iterate over MEM. Free unmarked items.
8. I saw this wino, he was eating grapes. I was like, “Dude, you have to wait.” -- MItch Hedberg
9. How can we make this better?
10. Idea: Combine the mark and sweep phase. (One pass)
11. Idea: Shorter pauses by doing less work more often. (Incremental)
12. Idea: Shorter pauses by doing less work more often. (Real- time)
13. Idea: "Most objects die young." Separate the heap into old and new. (Generational)
14. Yes We Can!
15. One Pass Real-Time Generational Mark-Sweep Garbage Collection Joe Armstrong, Robert Virding, 1995
16. def mark_all(): SCAV = most_recent_alloc while SCAV > min_heap_addr: if marked(SCAV): mark_pointers(SCAV) SCAV -= 1 SCAV min_heap_addr
17. def alloc(): obj = new() obj.previous =\ most_recent_alloc most_recent_alloc = obj return obj obj most_recent_alloc
18. def gc(): last_alloc = most_recent_alloc SCAV = last_alloc.previous while SCAV != first_alloc: if marked(SCAV): mark_pointers(SCAV) unmark(SCAV) last_alloc = SCAV SCAV = last_alloc.previous else: tmp = SCAV SCAV = SCAV.previous last_alloc.previous = SCAV free(tmp) tmp last_alloc new SCAV
19. BUT WAIT THERE’S MORE!!!!11
20. This is incremental!
21. This is generational!
22. But, is it practical?
23. Advantages 1. Shear Simplicity 2. Ease of extension 3. Objects get reused quickly
24. But, 303 See Other
25. Thanks! https://github.com/apg/bangbangcon http://apgwoz.com @apgwoz
26. Image Resources 1. "Spread the Gnus": https://secure.flickr. com/photos/puliarfanita/6026330732/in/photolist-abwwb1-6ApYxu-jEp8pV-c2eXqw-81LPL-wjjkT-4JZqBQ- 6o3mJG-9YRiUm-3t4km-Ahtjx-9YNqoc-pZvNx-7mis1-czaJeS-czaHES-aUfdNe-6UaPSX-693pNg-fb84D-3QZoJ5- 5gm73-5ugFB8-73u9hq-aB4ivt-PUDs-a1xmWo-c2h9qG-73riU-7dUFU7-f9n7iJ-Kmwk6-4H614e-6gmUKL-5QUPxX- mXKrB-mG5w-aZ9cUz-LV31W-acH9dy-JYgvQ-JYfUN-ER1PN-evG5H-8UAthy-PkV7c-7JFKr1-4vUig4-7afj6F-8V1EY6 2. “Billy Mays”: https://upload.wikimedia. org/wikipedia/commons/f/fa/Billy_Mays_Portrait_Cropped.jpg