/usr/lib/ruby/1.8/needle/lifecycle/singleton.rb is in libneedle-ruby1.8 1.3.0-1.
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# =============================================================================
# Copyright (c) 2004, Jamis Buck (jamis@37signals.com)
# All rights reserved.
#
# This source file is distributed as part of the Needle dependency injection
# library for Ruby. This file (and the library as a whole) may be used only as
# allowed by either the BSD license, or the Ruby license (or, by association
# with the Ruby license, the GPL). See the "doc" subdirectory of the Needle
# distribution for the texts of these licenses.
# -----------------------------------------------------------------------------
# needle website : http://needle.rubyforge.org
# project website: http://rubyforge.org/projects/needle
# =============================================================================
#++
require 'needle/pipeline/element'
require 'needle/thread'
module Needle
module Lifecycle
# The instantiation pipeline element that enforces the singleton
# multiplicity.
class Singleton < Needle::Pipeline::Element
set_default_priority 100
# Creates the mutex to use and sets the cached reference to +nil+.
def initialize_element
@mutex = QueryableMutex.new
@cached = nil
@is_cached = false
end
# Returns the cached reference, if it has been previously cached.
# Otherwise, invokes the next element in the pipeline and caches the
# result. The cached reference is returned.
def call( container, point )
unless @is_cached
@mutex.synchronize do
unless @is_cached
@cached = succ.call( container, point )
@is_cached = true
end
end
end
@cached
end
# Resets the cached singleton instance, so that the next time it is
# requested it is re-constructed.
def reset!
@mutex.synchronize do
@cached = nil
@is_cached = false
end
end
end
end
end
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