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# frozen_string_literal: true
# rubocop:todo all
# Copyright (C) 2016-2020 MongoDB Inc.
#
# Licensed under the Apache License, Version 2.0 (the 'License');
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an 'AS IS' BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
module Mongo
# This module abstracts the functionality for generating sequential
# unique integer IDs for instances of the class. It defines the method
# #next_id on the class that includes it. The implementation ensures that
# the IDs will be unique even when called from multiple threads.
#
# @example Include the Id module.
# class Foo
# include Mongo::Id
# end
#
# f = Foo.new
# foo.next_id # => 1
# foo.next_id # => 2
#
# Classes which include Id should _not_ access `@@id` or `@@id_lock`
# directly; instead, they should call `#next_id` in `#initialize` and save
# the result in the instance being created.
#
# @example Save the ID in the instance of the including class.
# class Bar
# include Mongo::Id
#
# attr_reader :id
#
# def initialize
# @id = self.class.next_id
# end
# end
#
# a = Bar.new
# a.id # => 1
# b = Bar.new
# b.id # => 2
#
# @since 2.7.0
# @api private
module Id
def self.included(klass)
klass.class_variable_set(:@@id, 0)
klass.class_variable_set(:@@id_lock, Mutex.new)
klass.define_singleton_method(:next_id) do
klass.class_variable_get(:@@id_lock).synchronize do
id = class_variable_get(:@@id)
klass.class_variable_set(:@@id, id + 1)
klass.class_variable_get(:@@id)
end
end
end
end
end
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