Class: RDF::Util::Cache

Inherits:
Object
  • Object
show all
Defined in:
lib/rdf/util/cache.rb

Overview

A ‘Hash`-like cache that holds only weak references to the values it caches, meaning that values contained in the cache can be garbage collected. This allows the cache to dynamically adjust to changing memory conditions, caching more objects when memory is plentiful, but evicting most objects if memory pressure increases to the point of scarcity.

While this cache is something of an internal implementation detail of RDF.rb, some external libraries do currently make use of it as well, including [SPARQL::Algebra](sparql.rubyforge.org/algebra/) and [Spira](spira.rubyforge.org/). Do be sure to include any changes here in the RDF.rb changelog.

See Also:

Since:

  • 0.2.0

Direct Known Subclasses

ObjectSpaceCache, WeakRefCache

Defined Under Namespace

Classes: ObjectSpaceCache, WeakRefCache

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(capacity = -1)) ⇒ Cache

Returns a new instance of Cache.

Parameters:

  • capacity (Integer) (defaults to: -1))

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 39

def initialize(capacity = -1)
  @capacity = capacity
  @cache  ||= {}
  @index  ||= {}
end

Class Method Details

.new(*args) ⇒ Object

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 22

def self.new(*args)
  # JRuby doesn't support `ObjectSpace#_id2ref` unless the `-X+O`
  # startup option is given.  In addition, ObjectSpaceCache is very slow
  # on Rubinius.  On those platforms we'll default to using
  # the WeakRef-based cache:
  if RUBY_PLATFORM == 'java' || (defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx')
    klass = WeakRefCache
  else
    klass = ObjectSpaceCache
  end
  cache = klass.allocate
  cache.send(:initialize, *args)
  cache
end

Instance Method Details

#define_finalizer!(value) ⇒ void

This method returns an undefined value.

Parameters:

  • value (Object)

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 60

def define_finalizer!(value)
  ObjectSpace.define_finalizer(value, finalizer)
end

#finalizer ⇒ Proc

Returns:

  • (Proc)

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 66

def finalizer
  lambda { |object_id| @cache.delete(@index.delete(object_id)) }
end

#has_capacity? ⇒ Boolean

Returns:

  • (Boolean)

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 53

def has_capacity?
  @capacity.equal?(-1) || @capacity > @cache.size
end

#size ⇒ Integer

Returns:

  • (Integer)

Since:

  • 0.2.0



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# File 'lib/rdf/util/cache.rb', line 47

def size
  @cache.size
end