PageException created and LRU,Second Chance Handling

1 files changed, 71 insertions, 0 deletions

diff --git a/lru.py b/lru.py
new file mode 100644
index 0000000..3042bba
--- /dev/null
+++ b/lru.py
@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+
+from mem import Memory
+from pageexception import *
+
+class LruPaginator:
+  def __init__(self, mem):
+    self.mem = mem
+    self._global_counter = 1
+    self._check_table = [0 for _ in range(len(mem.main)+len(mem.virt))]
+    self._main_cursor = 0
+  
+  def _update_check_table(self, page):
+    """
+    >>> lru = LruPaginator(Memory(3,5))
+    >>> page = 3
+    >>> lru._update_check_table(page)
+    >>> print(lru._check_table[page])
+    1
+    >>> print(lru._global_counter)
+    2
+    """
+    self._check_table[page] = self._global_counter
+    self._global_counter += 1
+
+  def _check_where_to_replace(self):
+    """
+    >>> lru = LruPaginator(Memory(3,5))
+    >>> lru._check_where_to_replace()
+    >>> print(lru._main_cursor)
+    0
+    >>> lru.mem.main = [3,4,2]
+    >>> lru._check_table = [1, 3, 6, 4, 5, 0, 0, 0]
+    >>> lru._check_where_to_replace()
+    >>> print(lru._main_cursor)
+    0
+    """
+    for page in self.mem.main:
+      if page is None:
+        self._main_cursor = self.mem.main.index(page)
+        return
+    min = self._check_table[self.mem.main[0]]
+    self._main_cursor = 0
+    for page in self.mem.main:
+      if min > self._check_table[page]:
+        min = self._check_table[page]
+        self._main_cursor = self.mem.main.index(page)
+
+  def _put_main(self, page):
+    self._check_where_to_replace()
+    print("Cursor:")
+    print(self._main_cursor)
+    print("")
+    overwritten = self.mem.main[self._main_cursor]
+    self.mem.main[self._main_cursor] = page
+    self._update_check_table(page)
+    return overwritten  
+        
+  def load(self, page):
+    if not self.mem.page_in_range(page): raise PageException
+    if page in self.mem.main: 
+      self._update_check_table(page)
+      return
+    if page in self.mem.virt: self.mem.remove_virt(page)
+    overwritten = self._put_main(page)
+    if overwritten is not None: self.mem.put_virt(overwritten)
+
+
+if __name__ == "__main__":
+  import doctest
+  doctest.testmod()