From 8edf2787fca77df7e17e25267f0e18d81667bedd Mon Sep 17 00:00:00 2001
From: Zac Medico <zmedico@gentoo.org>
Date: Sun, 26 Feb 2006 13:10:43 +0000
Subject: Add a new cache.metadata_overlay module that layers a writable cache
 over a readonly cache.

svn path=/main/trunk/; revision=2792
---
 pym/cache/metadata_overlay.py | 91 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 pym/cache/metadata_overlay.py

diff --git a/pym/cache/metadata_overlay.py b/pym/cache/metadata_overlay.py
new file mode 100644
index 000000000..557855a52
--- /dev/null
+++ b/pym/cache/metadata_overlay.py
@@ -0,0 +1,91 @@
+# Copyright 1999-2006 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+# $Header: $
+
+import time
+if not hasattr(__builtins__, "set"):
+	from sets import Set as set
+import template
+from flat_hash import database as db_rw
+from metadata import database as db_ro
+
+class database(template.database):
+
+	autocommits = True
+	serialize_eclasses = False
+
+	def __init__(self, location, label, auxdbkeys, **config):
+		super(database, self).__init__(location, label, auxdbkeys)
+		self.db_rw = db_rw(location, label, auxdbkeys, **config)
+		self.db_ro = db_ro(label,"metadata/cache",auxdbkeys)
+
+	def __getitem__(self, cpv):
+		"""funnel whiteout validation through here, since value needs to be fetched"""
+		try:
+			value = self.db_rw[cpv]
+		except KeyError:
+			return self.db_ro[cpv] # raises a KeyError when necessary
+		if self._is_whiteout(value):
+			if self._is_whiteout_valid(cpv, value):
+				raise KeyError(cpv)
+			else:
+				del self.db_rw[cpv]
+				return self.db_ro[cpv] # raises a KeyError when necessary
+		else:
+			return value
+
+	def _setitem(self, name, values):
+		try:
+			value_ro = self.db_ro[name]
+			if self._are_values_identical(value_ro,values):
+				# we have matching values in the underlying db_ro
+				# so it is unnecessary to store data in db_rw
+				try:
+					del self.db_rw[name] # delete unwanted whiteout when necessary
+				except KeyError:
+					pass
+		except KeyError:
+			self.db_rw[name] = values
+
+	def _delitem(self, cpv):
+		value = self[cpv] # validates whiteout and/or raises a KeyError when necessary
+		if self.db_ro.has_key(cpv):
+			self.db_rw[cpv] = self._create_whiteout(value)
+		else:
+			del self.db_rw[cpv]
+
+	def has_key(self, cpv):
+		try:
+			self[cpv] # validates whiteout when necessary
+		except KeyError:
+			return False
+		return True
+
+	def iterkeys(self):
+		s = set()
+		for cpv in self.db_rw.iterkeys():
+			if self.has_key(cpv): # validates whiteout when necessary
+				yield cpv
+			# set includes whiteouts so they won't be yielded later
+			s.add(cpv)
+		for cpv in self.db_ro.iterkeys():
+			if cpv not in s:
+				yield cpv
+
+	def _is_whiteout(self, value):
+		return value["EAPI"] == "whiteout"
+
+	def _create_whiteout(self, value):
+		return {"EAPI":"whiteout","_eclasses_":value["_eclasses_"],"_mtime_":value["_mtime_"]}
+
+	def _is_whiteout_valid(self, name, value_rw):
+		try:
+			value_ro = self.db_ro[name]
+			return self._are_values_identical(value_rw,value_ro)
+		except KeyError:
+			return False
+
+	def _are_values_identical(self, value1, value2):
+		if long(value1["_mtime_"]) != long(value2["_mtime_"]):
+			return False
+		return value1["_eclasses_"] == value2["_eclasses_"]
-- 
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