Module: WeakSet::StrongKeys

Defined in:
lib/weak_set/strong_keys.rb

Overview

This WeakSet strategy targets JRuby >= 9.4.6.0 and TruffleRuby >= 22. Older versions require additional indirections implemented in StrongSecondaryKeys:

The ObjectSpace::WeakMap on JRuby and TruffleRuby has strong keys and weak values. Thus, only the value object can be garbage collected to remove the entry while the key defines a strong object reference which prevents the key object from being garbage collected.

As a workaround, we use the element's object_id as a key. Being an Integer, the object_id is generally is not garbage collected anyway but allows to uniquely identity the object.

The WeakMaps do not allow to explicitly delete entries. We emulate this by setting the garbage-collectible value of a deleted entry to a simple new object. This value will be garbage collected on the next GC run which will then remove the entry. When accessing elements, we delete and filter out these recently deleted entries.

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.usable? ⇒ Bool

Checks if this strategy is usable for the current Ruby version.

Returns:

  • (Bool) —

    truethy for Ruby, TruffleRuby and modern JRuby, falsey otherwise



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# File 'lib/weak_set/strong_keys.rb', line 39

def self.usable?
  case RUBY_ENGINE
  when "ruby", "truffleruby"
    true
  when "jruby"
    Gem::Version.new(RUBY_ENGINE_VERSION) >= Gem::Version.new("9.4.6.0")
  end
end

Instance Method Details

#add(obj) ⇒ self

Adds the given object to the weak set and return self. Use WeakSet#merge to add many elements at once.

In contrast to other "regular" objects, we will not retain a strong reference to the added object. Unless some other live objects still references the object, it will eventually be garbage-collected.

Examples:

WeakSet[1, 2].add(3)                #=> #<WeakSet: {1, 2, 3}>
WeakSet[1, 2].add([3, 4])           #=> #<WeakSet: {1, 2, [3, 4]}>
WeakSet[1, 2].add(2)                #=> #<WeakSet: {1, 2}>

Parameters:

  • obj (Object) —

    an object

Returns:

  • (self) 


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# File 'lib/weak_set/strong_keys.rb', line 55

def add(obj)
  @map[obj.__id__] = obj
  self
end

#clear ⇒ self

Removes all elements and returns self

Returns:

  • (self) 


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# File 'lib/weak_set/strong_keys.rb', line 61

def clear
  @map = ObjectSpace::WeakMap.new
  self
end

#delete?(obj) ⇒ self?

Note:

WeakSet does not test member equality with == or eql?. Instead, it always checks strict object equality, so that, e.g., different strings are not considered equal, even if they may contain the same string content.

Deletes the given object from self and returns self if it was present in the set. If the object was not in the set, returns nil.

Parameters:

  • obj (Object)

Returns:

  • (self, nil) —

    self if the given object was deleted from the set or nil if the object was not part of the set



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# File 'lib/weak_set/strong_keys.rb', line 67

def delete?(obj)
  key = obj.__id__
  return unless @map.key?(key) && @map[key].equal?(obj)

  # If there is a valid value in the WeakMap (with a strong object_id
  # key), we replace the value of the strong key with a temporary
  # DeletedEntry object. As we do not keep any strong reference to this
  # object, this will cause the key/value entry to vanish from the WeakMap
  # when the DeletedEntry object is eventually garbage collected.
  @map[key] = DeletedEntry.new
  self
end

#each {|element| ... } ⇒ self, Enumerator

Calls the given block once for each live element in self, passing that element as a parameter. Returns the weak set itself.

If no block is given, an Enumerator is returned instead.

Yields:

  • (element) —

    calls the given block once for each element in self

Yield Parameters:

  • element (Object) —

    the yielded value

Returns:

  • (self, Enumerator) —

    self if a block was given or an Enumerator if no block was given.



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# File 'lib/weak_set/strong_keys.rb', line 81

def each
  return enum_for(__method__) { size } unless block_given?

  @map.values.each do |obj|
    yield(obj) unless DeletedEntry === obj
  end
  self
end

#include?(obj) ⇒ Bool

Note:

WeakSet does not test member equality with == or eql?. Instead, it always checks strict object equality, so that, e.g., different strings are not considered equal, even if they may contain the same string content.

Returns true if the given object is included in self, false otherwise.

Parameters:

  • obj (Object) —

    an object

Returns:

  • (Bool) —

    true if the given object is included in self, false otherwise



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# File 'lib/weak_set/strong_keys.rb', line 91

def include?(obj)
  key = obj.__id__
  !!(@map.key?(key) && @map[key].equal?(obj))
end

#initialize ⇒ void

initialize the weak map



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# File 'lib/weak_set/strong_keys.rb', line 50

def initialize
  @map = ObjectSpace::WeakMap.new
end

#size ⇒ Integer

Returns the number of live elements in self.

Returns:

  • (Integer) —

    the number of live elements in self



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# File 'lib/weak_set/strong_keys.rb', line 97

def size
  # Compared to using WeakMap#each_value like we do in WeakKeys, this
  # version is
  #   * ~12% faster on JRuby >= 9.4.6.0
  #   * sam-ish on TruffleRuby 24 with a slight advantage to this version
  @map.values.delete_if { |obj| DeletedEntry === obj }.size
end

#to_a ⇒ Array

Note:

The order of elements on the returned Array is non-deterministic. We do not preserve preserve insertion order.

Returns the live elements contained in self as an Array.

Returns:

  • (Array) —

    the live elements contained in self as an Array



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# File 'lib/weak_set/strong_keys.rb', line 106

def to_a
  @map.values.delete_if { |obj| DeletedEntry === obj }
end