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|
module Concurrent
module Synchronization
# @!visibility private
# @!macro internal_implementation_note
ObjectImplementation = case
when Concurrent.on_cruby?
MriObject
when Concurrent.on_jruby?
JRubyObject
when Concurrent.on_rbx?
RbxObject
when Concurrent.on_truffle?
TruffleObject
else
MriObject
end
private_constant :ObjectImplementation
# Abstract object providing final, volatile, ans CAS extensions to build other concurrent abstractions.
# - final instance variables see {Object.safe_initialization!}
# - volatile instance variables see {Object.attr_volatile}
# - volatile instance variables see {Object.attr_atomic}
class Object < ObjectImplementation
# TODO make it a module if possible
# @!method self.attr_volatile(*names)
# Creates methods for reading and writing (as `attr_accessor` does) to a instance variable with
# volatile (Java) semantic. The instance variable should be accessed oly through generated methods.
#
# @param [Array<Symbol>] names of the instance variables to be volatile
# @return [Array<Symbol>] names of defined method names
# Has to be called by children.
def initialize
super
initialize_volatile_with_cas
end
# By calling this method on a class, it and all its children are marked to be constructed safely. Meaning that
# all writes (ivar initializations) are made visible to all readers of newly constructed object. It ensures
# same behaviour as Java's final fields.
# @example
# class AClass < Concurrent::Synchronization::Object
# safe_initialization!
#
# def initialize
# @AFinalValue = 'value' # published safely, does not have to be synchronized
# end
# end
def self.safe_initialization!
# define only once, and not again in children
return if safe_initialization?
def self.new(*args, &block)
object = super(*args, &block)
ensure
object.full_memory_barrier if object
end
@safe_initialization = true
end
# @return [true, false] if this class is safely initialized.
def self.safe_initialization?
@safe_initialization = false unless defined? @safe_initialization
@safe_initialization || (superclass.respond_to?(:safe_initialization?) && superclass.safe_initialization?)
end
# For testing purposes, quite slow. Injects assert code to new method which will raise if class instance contains
# any instance variables with CamelCase names and isn't {.safe_initialization?}.
def self.ensure_safe_initialization_when_final_fields_are_present
Object.class_eval do
def self.new(*args, &block)
object = super(*args, &block)
ensure
has_final_field = object.instance_variables.any? { |v| v.to_s =~ /^@[A-Z]/ }
if has_final_field && !safe_initialization?
raise "there was an instance of #{object.class} with final field but not marked with safe_initialization!"
end
end
end
end
# Creates methods for reading and writing to a instance variable with
# volatile (Java) semantic as {.attr_volatile} does.
# The instance variable should be accessed oly through generated methods.
# This method generates following methods: `value`, `value=(new_value) #=> new_value`,
# `swap_value(new_value) #=> old_value`,
# `compare_and_set_value(expected, value) #=> true || false`, `update_value(&block)`.
# @param [Array<Symbol>] names of the instance variables to be volatile with CAS.
# @return [Array<Symbol>] names of defined method names.
def self.attr_atomic(*names)
@volatile_cas_fields ||= []
@volatile_cas_fields += names
safe_initialization!
define_initialize_volatile_with_cas
names.each do |name|
ivar = :"@Atomic#{name.to_s.gsub(/(?:^|_)(.)/) { $1.upcase }}"
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{name}
#{ivar}.get
end
def #{name}=(value)
#{ivar}.set value
end
def swap_#{name}(value)
#{ivar}.swap value
end
def compare_and_set_#{name}(expected, value)
#{ivar}.compare_and_set expected, value
end
def update_#{name}(&block)
#{ivar}.update(&block)
end
RUBY
end
names.flat_map { |n| [n, :"#{n}=", :"swap_#{n}", :"compare_and_set_#{n}", :"update_#{n}"] }
end
# @param [true,false] inherited should inherited volatile with CAS fields be returned?
# @return [Array<Symbol>] Returns defined volatile with CAS fields on this class.
def self.volatile_cas_fields(inherited = true)
@volatile_cas_fields ||= []
((superclass.volatile_cas_fields if superclass.respond_to?(:volatile_cas_fields) && inherited) || []) +
@volatile_cas_fields
end
private
def self.define_initialize_volatile_with_cas
assignments = @volatile_cas_fields.map { |name| "@Atomic#{name.to_s.gsub(/(?:^|_)(.)/) { $1.upcase }} = AtomicReference.new(nil)" }.join("\n")
class_eval <<-RUBY
def initialize_volatile_with_cas
super
#{assignments}
end
RUBY
end
private_class_method :define_initialize_volatile_with_cas
def initialize_volatile_with_cas
end
end
end
end
|
