Class: Cache::LRU

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/background_queue/server_lib/lru.rb

Overview

Defines a local LRU cache. All operations are maintained in constant size regardless of the size of the Cache. When creating the cache, you specify the max size of the cache.

Example:

cache = Cache::LRU.new(:max_elements => 5)
 cache.put(:a, 1)
 cache[:a] = 2
 cache.get(:b) { 1 }
 cache[:b]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(opts = {}) ⇒ LRU

opts:

- max_elements - maximum number of elements to keep in the
  cache at any time. The default is 100 elements



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# File 'lib/background_queue/server_lib/lru.rb', line 42

def initialize(opts = {})
  opts = { :max_elements => 100 }.merge(opts)
  @max_elements = opts.delete(:max_elements)
  raise "Invalid options: #{opts.keys.join(' ')}" if opts.keys.size > 0
  @keys = LinkedList.new
  @map = {}
  @size = 0
end

Instance Attribute Details

#keys ⇒ Object (readonly)

Returns the value of attribute keys.



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# File 'lib/background_queue/server_lib/lru.rb', line 38

def keys
  @keys
end

#size ⇒ Object (readonly)

Returns the value of attribute size.



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# File 'lib/background_queue/server_lib/lru.rb', line 37

def size
  @size
end

Instance Method Details

#[](key) ⇒ Object 



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# File 'lib/background_queue/server_lib/lru.rb', line 64

def [](key)
  get(key)
end

#[]=(key, value) ⇒ Object 



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# File 'lib/background_queue/server_lib/lru.rb', line 81

def []=(key, value)
  put(key, value)
end

#clear! ⇒ Object 



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# File 'lib/background_queue/server_lib/lru.rb', line 51

def clear!
  initialize( :max_elements => @max_elements )
end

#delete(key) ⇒ Object 



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# File 'lib/background_queue/server_lib/lru.rb', line 103

def delete(key) 
  if el = @map[key]
    delete_element(el)
    @size -= 1
  else
    nil
  end
end

#each ⇒ Object

Iterates through all of the key/value pairs added to the cache, in random order. Accepts a block that is yielded to with the key and value for each entry in the cache.



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# File 'lib/background_queue/server_lib/lru.rb', line 58

def each
  @map.each do |k, el| 
    yield k, el.value
  end
end

#get(key) ⇒ Object

Fetches the value of the element with the given key. If this key does not exist in the cache, you can provide an optional code block that we’ll yield to to repopulate the value



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# File 'lib/background_queue/server_lib/lru.rb', line 71

def get(key)
  if el = @map[key]
    @keys.move_to_head(el)
    return el.value
  elsif block_given?
    return put(key, yield)
  end
  return nil
end

#put(key, value) ⇒ Object 



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# File 'lib/background_queue/server_lib/lru.rb', line 85

def put(key, value)
  el = @map[key]
  if el
    el.value = value
    @keys.move_to_head(el)
  else
    el = @keys.add(key, value)
    @size += 1
  end
  @map[key] = el

  if @size > @max_elements
    delete_element(@keys.last) 
    @size -= 1
  end
  value
end