[SnowOne 2025] Александр Ланцов: Эволюция моделей памяти

Термин «модель памяти» — интересный и непростой для понимания, так как в него вкладывается множество различных смыслов.

Чтобы упростить его осознание, мы проведем историческую ретроспективу: от появления первых моделей памяти «в железе» до их современного состояния. Затем рассмотрим, какие модели памяти используются в популярных языках программирования — на примере Java, C++, Rust и Go, сравним их особенности и принципы. Кроме того, обсудим недавние исследования и перспективные подходы, которые могут появиться в будущем.

Цель доклада — помочь лучше разобраться в ключевых аспектах моделей памяти и показать, как они эволюционировали до сегодняшнего дня. Будет полезно всем, кто интересуется вопросами многопоточности и конкурентности.

Видео: https://youtu.be/W5aoIRAORlA

Transcript

6. 1967 1971 1972
8. vCPU 1 MOV [a] ← 0 ; MOV [b] ← 0 MOV [a] ← 1 MOV [b] ← 2 r2 = 2; r1 = 0 vCPU 2 MOV _r2 ← [b] MOV _r1 ← [a]
9. 1️⃣ MOV [a] ← _1_ 2️⃣ MOV [b] ← _2_ 3️⃣ MOV r2 ← [b] 4️⃣ MOV r1 ← [a] r2 = 2; r1 = 0
10. r2 = 2; r1 = 0
11. 2️⃣ MOV [a] ← _1_ 3️⃣ MOV [b] ← _2_ 1️⃣ MOV r2 ← [b] 4️⃣ MOV r1 ← [a] r2 = 2; r1 = 0
13. 1996 1999 2007 2009 2005
14. w w r Thread 1 Thread 2 CPU 1 CPU 2 Memory w r w w w Thread N CPU N r w w w
15. CPU 1 CPU 2 MOV [a] ← 0 ; MOV [b] ← 0 MOV [a] ← 1 MOV [b] ← 2 MOV r2 ← [b] MOV r1 ← [a] r2 = 2; r1 = 0
16. CPU 1 CPU 2 MOV [a] ← 0 ; MOV [b] ← 0 MOV [a] ← _1_ MOV r2 ← [b] MOV [b] ← _1_ MOV r1 ← [a] r2 = 0; r1 = 0
18. CPU 1 CPU 2 MOV [a] ← 0 ; MOV [b] ← 0 MOV [a] ← 1 MOV [b] ← 2 MOV r2 ← [b] MOV r1 ← [a] r2 = 2; r1 = 0
20. CPU 1 MOV [x] ← 0 MOV [x] ← 1 r1 = 1; r2 = 2; r3 = 2; r4 = 1 CPU 2 MOV [x] ← 2 CPU 3 MOV r1 ← [x] MOV r2 ← [x] CPU 4 MOV r3 ← [x] MOV r4 ← [x]
22. Thread 1 int x = 0 x = 1 r1 = 1; r2 = 2; r3 = 2; r4 = 1 Thread 2 x = 2 Thread 3 r1 = x r2 = x Thread 4 r3 = x r4 = x
23. ➜
24. (1996) Thread 1 Thread 2 _________int x___ = 0 volatile int flag = 0 ___x = 1 flag = 1 while (flag == 0) { sleep() } assert x == 1 _______________
25. (2004)
27. Thread 1 int x = 0 lock a__ x = 1 unlock a Thread 2 lock b__ x = 2 unlock b Thread 3 lock a________ lock b____ r1 = x x = r1 r2 = x unlock b__ unlock a______ r1 == r2
28. Thread 1 int x = 0 lock a__ x = 1 unlock a Thread 2 lock b__ x = 2 unlock b Thread 3 lock a________ lock b____ r1 = x x = r1 r2 = x unlock b__ unlock a______ r1 == r2
29. Thread 1 int x = 0 lock a__ x = 1 unlock a Thread 2 lock b__ x = 2 unlock b Thread 3 lock a________ lock b____ r1 = x r2 = x unlock b__ unlock a______ r1 == r2
30. Thread 1 int x = 0 lock a__ x = 1 unlock a Thread 2 lock b__ x = 2 unlock b Thread 3 lock a________ lock b____ r1 = x x = r1 r2 = x unlock b__ unlock a______ r1 == r2
31. Thread 1 int x = 0 lock a__ x = 1 unlock a Thread 2 lock b__ x = 2 unlock b Thread 3 lock a________ lock b____ r1 = x x = r1 r2 = x unlock b__ unlock a______ x = r1
33. (2011)
34. Thread 1 std::atomic<int> x = 0 std::atomic<int> y = 0 if (x.load(relaxed) == 1) y.store(1, relaxed) Thread 2 if (y.load(relaxed) == 1) x.store(1, relaxed) x = 1; y = 1
35. Thread 1 int a = 0 std::atomic<int> x = 0 std::atomic<int> y = 0 if (x.load(rlx) == 1) if (a == 1)_______ y.store(1, rlx) Thread 2 if (y.load(rlx) == 1) x.store(1, rlx) x = 0 ; y = 0 Thread 0 a = 1
36. Thread 1 int a = 0 std::atomic<int> x = 0 std::atomic<int> y = 0 if (x.load(rlx) == 1) if (a == 1)_______ y.store(1, rlx) Thread 2 if (y.load(rlx) == 1) x.store(1, rlx) Thread 0 a = 1 ➞
37. Thread 1 int a = 0 std::atomic<int> x = 0 std::atomic<int> y = 0 a = 1________________ if (x.load(rlx) == 1) if (a == 1)_______ y.store(1, rlx) Thread 2 if (y.load(rlx) == 1) x.store(1, rlx) Thread 0 ➞
41. 💀 ☠️ 2018
42. b == a + 10 b, a b = a + 10_ Thread 0
43. b == a + 10 c = a + 10_ //some code b = a + 10_ b, a Thread 1 Thread 0 c = 1 int c = 0
44. b == a + 10 t = a + 10_ c = t______ //some code b = t______ b, a Thread 1 Thread 0 c = 1 int c = 0
45. t = a + 10_ c = t______ //some code b = c______ b, a Thread 1 Thread 0 c = 1 int c = 0 b == a + 10
46. t = a + 10_ c = t______ //some code b = c______ b, a Thread 1 Thread 0 c = 1 int c = 0 b == a + 10
47. Thread 0 C c = new C() c.x = 42____ int a = c.x_ __ class C { int x } a == 42 a
48. Thread 0 C c = new C() c.x = 42____ int a = c.x_ global = c__ Thread 1 global.x = 7 class C { int x } C global = new C() a == 42 a
49. Thread 0 C c = new C() c.x = 42____ global = c__ int a = c.x_ Thread 1 global.x = 7 class C { int x } C global = new C() a == 42 a
50. (2022)