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I want to make a sequence diagram, as shown in the picture below.

Code:

documentclass{article}

usepackage{tikz}

usepackage{tikz-uml}



begin{document}



begin{tikzpicture}

begin{umlseqdiag}



umlobject[no ddots]{Thread1}

begin{umlfragment}[type=States, label= {shortstack{BufferState1 \ == \ BufferFree}}, inner xsep=10]

    begin{umlcallself}[op={shortstack{BufferState1=BufferOccupied}}, dt=5]{Thread1}

        begin{umlfragment}[type=loop, label= shortstack{Counter \ != \ Buffersize}, inner xsep=10]

            begin{umlcallself}[op={MakeProtocol(ProtoBuffer1)}]{Thread1}

            end{umlcallself}

        end{umlfragment}

        umlcreatecall[no ddots, dt=7, x=5]{Thread1}{Thread2}

        begin{umlcallself}[op={CliendSend()}, dt=7]{Thread2}

            begin{umlcall}[op={FreeBufferCB(BufferState1)}, type=asynchron]{Thread2}{Thread1}

            end{umlcall}

        end{umlcallself}

    end{umlcallself}

umlfpart[shortstack{BufferState2 \ == \ BufferFree}]

    begin{umlcallself}[op={shortstack{BufferState2=BufferOccupied}}]{Thread1}

        begin{umlfragment}[type=loop, label= shortstack{Counter \ != \ Buffersize}, inner xsep=10]

            begin{umlcallself}[op={MakeProtocol(ProtoBuffer2)}]{Thread1}

            end{umlcallself}

        end{umlfragment}

        begin{umlcall}[op={create}]{Thread1}{Thread2}

            begin{umlcallself}[op={CliendSend()}, y=5]{Thread2}

                begin{umlcall}[op={FreeBufferCB(BufferState2)}, type=asynchron ]{Thread2}{Thread1}

                end{umlcall}

            end{umlcallself}

        end{umlcall}

    end{umlcallself}

umlfpart[shortstack{BufferState1 \ == \ BufferOccupied \ && \ BufferState2 \ == \ BufferOccupied}]

    begin{umlcallself}[op={Exit(EXIT_FAILURE)}, padding=5]{Thread1}

    end{umlcallself}

end{umlfragment}



end{umlseqdiag}

end{tikzpicture}    



end{document}

Now i want to shift a few things, as shown with the red arrows in the picture. The red squares are the parts i want to cut, to make these boxes shorter. Is there a way to do this?

This generates a lot of errors when building. Most of them are from the shortstack instruction. Is there are correct way to make this newline?

Thank you for your help!