Class: LazyList::ReadQueue

Inherits:
Object show all
Defined in:
lib/lazylist.rb

Overview

ReadQueue is the implementation of an read-only queue that only supports #shift and #empty? methods. It’s used as a wrapper to encapsulate enumerables in lazy lists.

Instance Method Summary collapse

Constructor Details

#initialize(enumerable) ⇒ ReadQueue

Creates an ReadQueue object from an enumerable.



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# File 'lib/lazylist.rb', line 139

def initialize(enumerable)
  @data = []
  @producer = Thread.new do
    Thread.stop
    begin
      enumerable.each do |value|
        old, Thread.critical = Thread.critical, true
        begin
          @data << value
          @consumer.wakeup
          Thread.stop
        ensure
          Thread.critical = old
        end
      end
    rescue => e
      @consumer.raise e
    ensure
      @consumer.wakeup
    end
  end
  Thread.pass until @producer.stop?
end

Instance Method Details

#empty? ⇒ Boolean

Returns true if the queue is empty.



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# File 'lib/lazylist.rb', line 176

def empty?
  if @data.empty?
    old, Thread.critical = Thread.critical, true
    begin
      @consumer = Thread.current
      @producer.wakeup
      Thread.stop
    rescue ThreadError
      ;
    ensure
      @consumer = nil
      Thread.critical = old
    end
  end
  @data.empty?
end

#shift ⇒ Object Also known as: pop

Extracts the top element from the queue or nil if the queue is empty.



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# File 'lib/lazylist.rb', line 165

def shift
  if empty?
    nil
  else
    @data.shift
  end
end