class Atomic

def compare_and_set(old_value, new_value)
  return false unless @mutex.try_lock
  begin
    return false unless @value.equal? old_value
    @value = new_value
  ensure
    @mutex.unlock
  end
  true
end

def compare_and_set(expected, new)
  if expected.kind_of? Numeric
    while true
      old = get
      
      return false unless old.kind_of? Numeric
      
      return false unless old == expected
      
      result = _compare_and_set(old, new)
      return result if result
    end
  else
    _compare_and_set(expected, new)
  end
end

def get
  @mutex.synchronize { @value }
end

def get_and_set(new_value)
  @mutex.synchronize do
    old_value = @value
    @value = new_value
    old_value
  end
end

def initialize(value = nil)
  @mutex = Mutex.new
  @value = value
end

def set(new_value)
  @mutex.synchronize { @value = new_value }
end

def try_update
  old_value = @ref.get
  new_value = yield old_value
  unless @ref.compare_and_set(old_value, new_value)
    if $VERBOSE
      raise ConcurrentUpdateError, "Update failed"
    else
      raise ConcurrentUpdateError, "Update failed", ConcurrentUpdateError::CONC_UP_ERR_BACKTRACE
    end
  end
  new_value
end

def try_update
  old_value = get
  new_value = yield old_value
  unless compare_and_set(old_value, new_value)
    if $VERBOSE
      raise ConcurrentUpdateError, "Update failed"
    else
      raise ConcurrentUpdateError, "Update failed", ConcurrentUpdateError::CONC_UP_ERR_BACKTRACE
    end
  end
  new_value
end

def update
  true until @ref.compare_and_set(old_value = @ref.get, new_value = yield(old_value))
  new_value
end

def update
  true until compare_and_set(old_value = get, new_value = yield(old_value))
  new_value
end