/usr/lib/ruby/1.8/ramaze/snippets/ramaze/lru_hash.rb is in libramaze-ruby1.8 2010.06.18-2.
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# A Hash-alike LRU cache that provides fine-grained control over content
# restrictions.
#
# It allows you to set:
# * a maximum number of elements
# * the maximum amount of memory used for all elements
# * the allowed memory-size per element
# * time to live
#
# Differences to the original implementation include:
# * The Cache is now a Struct for speed
# * Object memory size is obtained via Marshal::dump instead of #to_s
#
# Note that due to calculating object size with Marshal, you might have to do
# some evaluation as to how large your values will be when marshaled, for
# example a String will have String#size + 10. This differs from object to
# object and between versions of Marshal, so be generous.
#
# Copyright (C) 2002 Yoshinori K. Okuji <okuji@enbug.org>
# Copyright (c) 2009 Michael Fellinger <manveru@rubyists.com>
#
# You may redistribute it and/or modify it under the same terms as Ruby.
class LRUHash < Struct.new(:max_total, :max_value, :max_count, :expiration,
:hook, :objs, :total_size, :list, :hits, :misses)
CacheObject = Struct.new(:content, :size, :atime)
VERSION = '0.3'
# On 1.8 we raise IndexError, on 1.9 we raise KeyError
KeyError = Module.const_defined?(:KeyError) ? KeyError : IndexError
include Enumerable
def initialize(options = {}, &hook)
self.max_value = options[:max_value]
self.max_total = options[:max_total]
self.max_count = options[:max_count]
self.expiration = options[:expiration]
avoid_insane_options
self.hook = hook
self.objs = {}
self.list = []
self.total_size = 0
self.hits = self.misses = 0
end
def key?(key)
objs.key?(key)
end
def value?(given_value)
objs.each do |key, obj|
return true if given_value == obj.content
end
false
end
def index(given_value)
objs.each do |key, obj|
return key if given_value == obj.content
end
nil
end
def keys
objs.keys
end
def size
objs.size
end
alias length size
def to_hash
objs.dup
end
def values
objs.map{|key, obj| obj.content }
end
def delete(key)
return unless objs.key?(key)
obj = objs[key]
hook.call(key, obj.content) if hook
self.total_size -= obj.size
objs.delete key
list.delete_if{|list_key| key == list_key }
obj.content
end
alias invalidate delete
def clear
objs.each{|key, obj| hook.call(key, obj) } if hook
objs.clear
list.clear
self.total_size = 0
end
alias invalidate_all clear
def expire
return unless expiration
now = Time.now.to_i
list.each_with_index do |key, index|
break unless (objs[key].atime + expiration) <= now
invalidate key
end
end
def [](key)
expire
unless objs.key?(key)
self.misses += 1
return
end
obj = objs[key]
obj.atime = Time.now.to_i
list.delete_if{|list_key| key == list_key }
list << key
self.hits += 1
obj.content
end
def []=(key, obj)
expire
invalidate key if key?(key)
size = Marshal.dump(obj).size
if max_value && max_value < max_total
warn "%p isn't cached because it exceeds max_value %p" % [obj, max_value]
return obj
end
if max_value.nil? && max_total && max_total < size
warn "%p isn't cached because it exceeds max_total: %p" % [obj, max_total]
return obj
end
invalidate list.first if max_count && max_count == list.size
self.total_size += size
if max_total
invalidate list.first until total_size < max_total
end
objs[key] = CacheObject.new(obj, size, Time.now.to_i)
list << key
obj
end
def store(key, value)
self[key] = value
end
def each_pair
return enum_for(:each_pair) unless block_given?
objs.each{|key, obj| yield key, obj.content }
self
end
def each_key(&block)
return enum_for(:each_key) unless block_given?
objs.each_key{|key| yield key }
self
end
def each_value
return enum_for(:each_value) unless block_given?
objs.each_value{|obj| yield obj.content }
self
end
def empty?
objs.empty?
end
# Note that this method diverges from the default behaviour of the Ruby Hash.
# If the cache doesn't find content for the given key, it will store the
# given default instead. Optionally it also takes a block, the return value
# of the block is then stored and returned.
#
# @usage Example
#
# lru = LRUHash.new
# lru.fetch(:a) # => KeyError: key not found: :a
# lru.fetch(:a, :b) # => :b
# lru.fetch(:a) # => :b
# lru.fetch(:c){|key| key.to_s } # => 'c'
# lru.fetch(:c) # => 'c'
def fetch(key, default = (p_default = true; nil))
if key?(key)
value = self[key]
elsif p_default.nil?
value = self[key] = default
elsif block_given?
value = self[key] = yield(key)
else
raise KeyError, "key not found: %p" % [key]
end
value
end
def statistics
{:size => total_size, :count => list.size, :hits => hits, :misses => misses}
end
private
# Sanity checks.
def avoid_insane_options
if (max_value && max_total) && max_value > max_total
raise ArgumentError, "max_value exceeds max_total (#{max_value} > #{max_total})"
end
if max_value && max_value <= 0
raise ArgumentError, "invalid max_value `#{max_value}'"
end
if max_total && max_total <= 0
raise ArgumentError, "invalid max_total `#{max_total}'"
end
if max_count && max_count <= 0
raise ArgumentError, "invalid max_count `#{max_count}'"
end
if expiration && expiration <= 0
raise ArgumentError, "invalid expiration `#{expiration}'"
end
end
end
end
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