\begin{frame}
  \frametitle{Pessimistic: Lock-based Concurrency Control}

  \begin{exampleblock}{Schedule with explicit lock actions}
  \begin{center}
    {\def\scheduleWidth{1cm}
    \begin{tikzpicture}
      \schedule{}{2}{2sA|2rA|1xB|1wB|1uB|2xB|2wB|2uA|2uB}
    \end{tikzpicture}
    }
  \end{center}
  Here we use the following abbreviations:
  \begin{itemize}
    \item $\tshared{A} = $ shared lock on $A$
    \item $\texclusive{A} = $ exclusive lock on $A$
    \item $\tunlock{A} = $ unlock $A$, or if more precision is needed
      \begin{itemize}
        \item $\tunlocks{A} = $ unlock shared lock on $A$
        \item $\tunlockx{A} = $ unlock exclusive lock on $A$
      \end{itemize}
  \end{itemize}
  \end{exampleblock}
\end{frame}