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udpquieck.tex

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+\subsection{UDPquieck}
+At SinQ a requirement is that newly created data files are automatically
+copied to another computer. This is for data safety. To have this done by
+the instrument control program would raise stability problems: what to do
+when the remote computer fails, when transfers are to slow or all data has
+to be transferred again. Therefore the copying of files was delegated to a
+second process. Now a a means is needed to tell the second process, that a
+new data file has been created. This means is this module. It sends a UDP
+message on a predefined port. The data copying process can receive or not
+and act accordingly. Furthermore this scheme can be used to have other 
+processes act upon a new data file as well. The message sent is simple: it
+consists of the string QUIECK/ followed by the filename. A new command is
+implemented with the name udpquieck. This shall be a hidden command. As only
+one such facility is needed for a given SICS server, all necessary data is
+held in the implementation file udpquieck.c. Anyway, there is only one 
+structure holding network data. 
+The configuration of the udpport is done via a special server
+option QuieckPort. 
+
+Laater on this facility may be extended to send arbitrary messages to
+the UDP port for further coordination tasks. This is catered for by
+having different message types. However, as of now only file messages
+are supported. 
+
+Needless to say, that the second process must be able to interpret the
+uDP messages sent by the SICS server.
+
+
+
+The following interface is implemented:
+
+\begin{flushleft} \small
+\begin{minipage}{\linewidth} \label{scrap1}
+$\langle$quieck {\footnotesize ?}$\rangle\equiv$
+\vspace{-1ex}
+\begin{list}{}{} \item
+\mbox{}\verb@@\\
+\mbox{}\verb@@\\
+\mbox{}\verb@#define QUIECK 1@\\
+\mbox{}\verb@@\\
+\mbox{}\verb@   void KillQuieck(void *pData);@\\
+\mbox{}\verb@@\\
+\mbox{}\verb@   int SendQuieck(int iType, char *filename);@\\
+\mbox{}\verb@@\\
+\mbox{}\verb@   int QuieckAction(SConnection *pCon, SicsInterp *pSics, void *pData,@\\
+\mbox{}\verb@                    int argc, char *argv[]);@\\
+\mbox{}\verb@@\\
+\mbox{}\verb@@$\diamond$
+\end{list}
+\vspace{-1ex}
+\footnotesize\addtolength{\baselineskip}{-1ex}
+\begin{list}{}{\setlength{\itemsep}{-\parsep}\setlength{\itemindent}{-\leftmargin}}
+\item Macro referenced in scrap ?.
+\end{list}
+\end{minipage}\\[4ex]
+\end{flushleft}
+\begin{flushleft} \small
+\begin{minipage}{\linewidth} \label{scrap2}
+\verb@"udpquieck.h"@ {\footnotesize ? }$\equiv$
+\vspace{-1ex}
+\begin{list}{}{} \item
+\mbox{}\verb@@\\
+\mbox{}\verb@/*------------------------------------------------------------------------@\\
+\mbox{}\verb@                   U D P Q U I E C K@\\
+\mbox{}\verb@ @\\
+\mbox{}\verb@  udpquieck sends a notification message on a UDP port when a new data@\\
+\mbox{}\verb@  file has been created. @\\
+\mbox{}\verb@@\\
+\mbox{}\verb@  Mark Koennecke, August 1998@\\
+\mbox{}\verb@---------------------------------------------------------------------------*/@\\
+\mbox{}\verb@#ifndef UDPQUIECK@\\
+\mbox{}\verb@#define UDPQUIECK@\\
+\mbox{}\verb@@$\langle$quieck {\footnotesize ?}$\rangle$\verb@@\\
+\mbox{}\verb@#endif@\\
+\mbox{}\verb@@$\diamond$
+\end{list}
+\vspace{-2ex}
+\end{minipage}\\[4ex]
+\end{flushleft}
+The functions:
+\begin{description}
+\item[KillQuieck] closes the network port at shutdown. Is the
+KillFunction used in the SICS interpreter command structure.
+\item[SendQuieck] sends a message of type iType and the text filename
+to the UDP port. The only supported iType value is QUIECK as defined
+in udpquieck.h. Further message types can be supported by adding more
+support in this function.
+\item[QuieckAction] is the interpreter interface function to this
+facility. Yes, messages may be issued by a commadn from the
+interpreter for instance within scripts. Again, this seems more useful
+when this facility has been extended.  
+\end{description}
+
+