# File lib_wpm/wpm.rb, line 3786
    def fetch(path, page_id)
      @lock.synchronize{
        if (cache_ref = @map[[path, page_id]]) then
          begin
            if (cache_ref.weakref_alive?) then
              return cache_ref.__getobj__
            end
          rescue WeakRef::RefError
            # nothing to do.
          end
          @map.delete([path, page_id])
        end
      }

      nil
    end