code: public final long getMappedLength() {
          MappedByteBuffer[] mmapArray = _mmapArray;
          long length = 0;
          
          if (mmapArray != null) {
              for (MappedByteBuffer mmap : mmapArray) {
                  length += mmap.capacity();
              }
          }
          
          return length;
      }
docs: Gets the total number of bytes of all mapped buffers.