Class: WeakHash

Inherits:
Object
  • Object
show all
Defined in:
lib/weak_hash.rb

Overview

This is a Hash where an association is removed as soon as either the key or the value are GCed.

When storing a value, the key is cloned and used in an internal hash (the cache) referetting to the object_id of the corresponding value.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(cache = Hash.new) ⇒ WeakHash

Returns a new instance of WeakHash.



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# File 'lib/weak_hash.rb', line 16

def initialize( cache = Hash.new )
  @cache = cache
  @key_map = {}
  @rev_cache = Hash.new{|h,k| h[k] = {}}

  @reclaim_value = lambda do |value_id|
    if @rev_cache.has_key? value_id
      @rev_cache[value_id].each_key{|key| @cache.delete key}
      @rev_cache.delete value_id
    end
  end

  @reclaim_key = lambda do |key_id|
    if @key_map.has_key? key_id
      @cache.delete @key_map[key_id]
    end
  end
end

Instance Attribute Details

#cache ⇒ Object (readonly)

Returns the value of attribute cache.



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# File 'lib/weak_hash.rb', line 14

def cache
  @cache
end

Instance Method Details

#[](key) ⇒ Object

retrieve object with the given key returns the object if present and it has not been garbage collected. Otherwise it returns nil.



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# File 'lib/weak_hash.rb', line 38

def []( key )
  value_id = @cache[key]
  return ObjectSpace._id2ref(value_id) unless value_id.nil?
  nil
rescue RangeError
  nil
end

#[]=(key, value) ⇒ Object

“store” object into the weak hash using the given key a weak reference is stored so the object stays references as long as it isn’t garbage collected.



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# File 'lib/weak_hash.rb', line 49

def []=( key, value )
  case key
  when Fixnum, Symbol, true, false, nil
    key2 = key
  else
    key2 = key.dup
  end

  @rev_cache[value.object_id][key2] = true
  @cache[key2] = value.object_id
  @key_map[key.object_id] = key2

  begin
    ObjectSpace.define_finalizer(value, @reclaim_value)
  rescue ArgumentError
    # Some objects will never be reclaimed by ObjectSpace, e.g. Fixnums
  end

  begin
    ObjectSpace.define_finalizer(key, @reclaim_key)
  rescue ArgumentError
    # Some objects will never be reclaimed by ObjectSpace, e.g. Fixnums
  end
end

#update(hash) ⇒ Object

an addition to Mauricio’s implementation, simple method that act’s like Hash#update method.



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# File 'lib/weak_hash.rb', line 76

def update(hash)
  hash.each { |key, val| send(:[]=, key, val) }
  self
end