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| 1 | +use std::collections::HashMap; |
| 2 | + |
| 3 | +use super::{spec::PageNumber, Page}; |
| 4 | + |
| 5 | +const PIN_LIMIT_PERCENT: f32 = 50.0; |
| 6 | +const MAX_CACHE_SIZE: usize = 1024; |
| 7 | + |
| 8 | +pub enum FrameFlags { |
| 9 | + REF = 0b001, |
| 10 | + DIRTY = 0b010, |
| 11 | + PINNED = 0b100, |
| 12 | +} |
| 13 | + |
| 14 | +#[derive(Clone)] |
| 15 | +pub struct Frame { |
| 16 | + pub page: Page, |
| 17 | + pub page_number: PageNumber, |
| 18 | + flags: u8, |
| 19 | +} |
| 20 | + |
| 21 | +impl Frame { |
| 22 | + pub fn new(page: Page, page_number: PageNumber) -> Self { |
| 23 | + Self { |
| 24 | + page, |
| 25 | + page_number, |
| 26 | + flags: FrameFlags::REF as u8, |
| 27 | + } |
| 28 | + } |
| 29 | + |
| 30 | + pub fn set(&mut self, flag: FrameFlags) { |
| 31 | + self.flags |= flag as u8 |
| 32 | + } |
| 33 | + |
| 34 | + pub fn unset(&mut self, flag: FrameFlags) { |
| 35 | + self.flags &= !(flag as u8) |
| 36 | + } |
| 37 | + |
| 38 | + pub fn has(&self, flag: FrameFlags) -> bool { |
| 39 | + self.flags & (flag as u8) != 0 |
| 40 | + } |
| 41 | +} |
| 42 | + |
| 43 | +type FrameNumber = usize; |
| 44 | + |
| 45 | +pub struct CacheBuilder { |
| 46 | + max_size: usize, |
| 47 | + pin_limit_percent: f32, |
| 48 | +} |
| 49 | + |
| 50 | +impl Default for CacheBuilder { |
| 51 | + fn default() -> Self { |
| 52 | + CacheBuilder::new() |
| 53 | + } |
| 54 | +} |
| 55 | + |
| 56 | +impl CacheBuilder { |
| 57 | + pub fn new() -> Self { |
| 58 | + Self { |
| 59 | + max_size: MAX_CACHE_SIZE, |
| 60 | + pin_limit_percent: PIN_LIMIT_PERCENT, |
| 61 | + } |
| 62 | + } |
| 63 | + |
| 64 | + pub fn max_size(mut self, size: usize) -> Self { |
| 65 | + self.max_size = size; |
| 66 | + self |
| 67 | + } |
| 68 | + |
| 69 | + pub fn pin_limit_percent(mut self, percent: f32) -> Self { |
| 70 | + self.pin_limit_percent = percent; |
| 71 | + self |
| 72 | + } |
| 73 | + |
| 74 | + pub fn build(self) -> Cache { |
| 75 | + Cache { |
| 76 | + buffer: Vec::new(), |
| 77 | + pages: HashMap::new(), |
| 78 | + clock_hand: 0, |
| 79 | + pinned: 0, |
| 80 | + max_size: self.max_size, |
| 81 | + pin_limit_percent: self.pin_limit_percent, |
| 82 | + } |
| 83 | + } |
| 84 | +} |
| 85 | + |
| 86 | +pub struct Cache { |
| 87 | + buffer: Vec<Frame>, |
| 88 | + pages: HashMap<PageNumber, FrameNumber>, |
| 89 | + clock_hand: FrameNumber, |
| 90 | + max_size: usize, |
| 91 | + |
| 92 | + pin_limit_percent: f32, |
| 93 | + pinned: usize, |
| 94 | +} |
| 95 | + |
| 96 | +impl Cache { |
| 97 | + pub fn contains(&self, page_number: PageNumber) -> bool { |
| 98 | + self.pages.contains_key(&page_number) |
| 99 | + } |
| 100 | + |
| 101 | + pub fn len(&self) -> usize { |
| 102 | + self.pages.len() |
| 103 | + } |
| 104 | + |
| 105 | + pub fn is_empty(&self) -> bool { |
| 106 | + self.pages.is_empty() |
| 107 | + } |
| 108 | + |
| 109 | + pub fn put(&mut self, page_number: PageNumber, page: Page) -> Option<Frame> { |
| 110 | + if let Some(idx) = self.pages.get(&page_number) { |
| 111 | + let entry = &mut self.buffer[*idx]; |
| 112 | + |
| 113 | + entry.page = page; |
| 114 | + |
| 115 | + return None; |
| 116 | + } |
| 117 | + |
| 118 | + if self.buffer.len() < self.max_size { |
| 119 | + self.buffer.push(Frame::new(page, page_number)); |
| 120 | + self.pages.insert(page_number, self.buffer.len() - 1); |
| 121 | + |
| 122 | + None |
| 123 | + } else { |
| 124 | + self.replace(page_number, page) |
| 125 | + } |
| 126 | + } |
| 127 | + |
| 128 | + pub fn get(&mut self, page_number: PageNumber) -> Option<&Page> { |
| 129 | + match self.pages.get(&page_number) { |
| 130 | + None => None, |
| 131 | + Some(idx) => { |
| 132 | + let frame = &mut self.buffer[*idx]; |
| 133 | + |
| 134 | + frame.set(FrameFlags::REF); |
| 135 | + Some(&frame.page) |
| 136 | + } |
| 137 | + } |
| 138 | + } |
| 139 | + |
| 140 | + fn get_frame_mut(&mut self, page_number: PageNumber) -> Option<&mut Frame> { |
| 141 | + match self.pages.get(&page_number) { |
| 142 | + None => None, |
| 143 | + Some(idx) => { |
| 144 | + let frame = &mut self.buffer[*idx]; |
| 145 | + |
| 146 | + Some(frame) |
| 147 | + } |
| 148 | + } |
| 149 | + } |
| 150 | + |
| 151 | + pub fn peek(&mut self, page_number: PageNumber) -> Option<&Page> { |
| 152 | + match self.pages.get(&page_number) { |
| 153 | + None => None, |
| 154 | + Some(idx) => Some(self.buffer.get(*idx).map(|entry| &entry.page).unwrap()), |
| 155 | + } |
| 156 | + } |
| 157 | + |
| 158 | + fn replace(&mut self, page_number: PageNumber, page: Page) -> Option<Frame> { |
| 159 | + let mut attempts = 0; |
| 160 | + |
| 161 | + while attempts < self.pages.len() { |
| 162 | + let index = self.clock_hand % self.pages.len(); |
| 163 | + let frame = &mut self.buffer[index]; |
| 164 | + |
| 165 | + if frame.has(FrameFlags::PINNED) { |
| 166 | + self.clock_hand = (self.clock_hand + 1) % self.pages.len(); |
| 167 | + attempts += 1; |
| 168 | + continue; |
| 169 | + } |
| 170 | + |
| 171 | + if frame.has(FrameFlags::REF) { |
| 172 | + frame.unset(FrameFlags::REF); |
| 173 | + self.clock_hand = (self.clock_hand + 1) % self.pages.len(); |
| 174 | + attempts += 1; |
| 175 | + |
| 176 | + continue; |
| 177 | + } |
| 178 | + |
| 179 | + let mut dirty_page = None; |
| 180 | + if frame.has(FrameFlags::DIRTY) { |
| 181 | + dirty_page = Some(frame.clone()); |
| 182 | + } |
| 183 | + |
| 184 | + *frame = Frame::new(page, page_number); |
| 185 | + |
| 186 | + self.clock_hand = (self.clock_hand + 1) % self.pages.len(); |
| 187 | + return dirty_page; |
| 188 | + } |
| 189 | + |
| 190 | + None |
| 191 | + } |
| 192 | + |
| 193 | + pub fn pin(&mut self, page_number: PageNumber) -> bool { |
| 194 | + let pinned_percentage = self.pinned as f32 / self.max_size as f32 * 100.0; |
| 195 | + |
| 196 | + if pinned_percentage >= self.pin_limit_percent { |
| 197 | + return false; |
| 198 | + } |
| 199 | + |
| 200 | + match self.get_frame_mut(page_number) { |
| 201 | + None => false, |
| 202 | + Some(frame) => { |
| 203 | + frame.set(FrameFlags::PINNED); |
| 204 | + self.pinned += 1; |
| 205 | + true |
| 206 | + } |
| 207 | + } |
| 208 | + } |
| 209 | + |
| 210 | + pub fn unpin(&mut self, page_number: PageNumber) -> bool { |
| 211 | + match self.get_frame_mut(page_number) { |
| 212 | + None => false, |
| 213 | + Some(frame) => { |
| 214 | + frame.unset(FrameFlags::PINNED); |
| 215 | + self.pinned -= 1; |
| 216 | + true |
| 217 | + } |
| 218 | + } |
| 219 | + } |
| 220 | + |
| 221 | + pub fn dirty(&mut self, page_number: PageNumber, page: Page) -> bool { |
| 222 | + match self.get_frame_mut(page_number) { |
| 223 | + None => false, |
| 224 | + Some(frame) => { |
| 225 | + frame.page = page; |
| 226 | + frame.set(FrameFlags::DIRTY); |
| 227 | + true |
| 228 | + } |
| 229 | + } |
| 230 | + } |
| 231 | +} |
| 232 | + |
| 233 | +#[cfg(test)] |
| 234 | +mod cache_tests { |
| 235 | + use super::*; |
| 236 | + |
| 237 | + #[test] |
| 238 | + fn put_test() { |
| 239 | + let mut cache = CacheBuilder::new().max_size(2).build(); |
| 240 | + |
| 241 | + cache.put(0, Page::create(0).unwrap()); |
| 242 | + cache.put(1, Page::create(0).unwrap()); |
| 243 | + |
| 244 | + assert_eq!(cache.len(), 2); |
| 245 | + } |
| 246 | + |
| 247 | + #[test] |
| 248 | + fn contains_test() { |
| 249 | + let mut cache = CacheBuilder::new().max_size(4).build(); |
| 250 | + let page = Page::create(0).unwrap(); |
| 251 | + let page1 = Page::create(0).unwrap(); |
| 252 | + let page2 = Page::create(0).unwrap(); |
| 253 | + let page3 = Page::create(0).unwrap(); |
| 254 | + |
| 255 | + cache.put(0, page.clone()); |
| 256 | + cache.put(1, page1.clone()); |
| 257 | + cache.put(2, page2.clone()); |
| 258 | + cache.put(3, page3.clone()); |
| 259 | + |
| 260 | + assert!(cache.contains(0)); |
| 261 | + assert!(cache.contains(1)); |
| 262 | + assert!(cache.contains(2)); |
| 263 | + assert!(cache.contains(3)); |
| 264 | + } |
| 265 | +} |
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