=================================================================== RCS file: /home/cvs/OpenXM/doc/issac2000/session-management.tex,v retrieving revision 1.2 retrieving revision 1.6 diff -u -p -r1.2 -r1.6 --- OpenXM/doc/issac2000/session-management.tex 2000/01/02 07:32:12 1.2 +++ OpenXM/doc/issac2000/session-management.tex 2000/01/15 00:20:46 1.6 @@ -1,8 +1,151 @@ -% $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.1 1999/12/23 10:25:09 takayama Exp $ +% $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.5 2000/01/11 05:35:48 noro Exp $ -\section{Session Management} (Noryo) - -MEMO: key words: -Security (ssh PAM), initial negotiation of byte order, -mathcap, interruption, debugging window, etc. - \ No newline at end of file +\section{Session Management} +\label{secsession} +%MEMO: key words: +%Security (ssh PAM), initial negotiation of byte order, +%mathcap, interruption, debugging window, etc. + +In this section we show the realization of control integration in +OpenXM. In OpenXM it is assumed that various clients and servers +establish connections dynamically and communicate to each +other. Therefore it is necessary to unify the communication interface +and the method of communication establishment. Besides, interruption +of an execution and debugging are common operations when we use +programming systems. OpenXM provides a method to realize them for +distributed computation. + +\subsection{Interface of servers} + +A server has additional I/O streams for exchanging data between +a client and itself other than ones for diagnostic +messages. As the streams are for binary data, +the byte order conversion is necessary when a +client and a server have different byte orders. It is determined by +exchanging the preferable byte order of each peer. If the preference +does not coincides with each other, +then the network byte order is used. +This implies that all servers and clients should be able to +handle the network byte +order. Nevertheless it is necessary to negotiate the byte order to +skip the byte order conversion because its cost is often dominant over +fast networks. + +\subsection{Invocation of servers} +\label{launcher} + +In general it is complicated to establish a connection over TCP/IP. +On the other hand a server itself does not have any function to +make a connection. In order to fill this gap an application called +{\bf launcher} is provided. A connection is established by using +the launcher as follows. + +\begin{enumerate} +\item A launcher is invoked from a client or by hand. +When the launcher is invoked, a port number for TCP/IP connection +and the name of a server should be informed. +\item The launcher and the client establish a connection with the +specified port number. +\item The launcher create a process and execute the server after +setting the binary I/O channels appropriately. +\end{enumerate} + +Though the above is all the task as a launcher, the launcher process +acts as a control server and controls the server process created by +itself. As for a control server see Section \ref{control}. + +\subsection{Control server} +\label{control} +When we use a mathematical software, an execution time or necessary +storage is often unknown in advance. Therefore it is desirable +to be able to abort an execution and to start another execution. +On OpenXM we adopted the following simple and robust method. + +An OpenXM server has logically two I/O channels: one for exchanging +data for computations and the other for controlling computations. The +control channel is used to send commands to control execution on the +server. The launcher introduced in Section \ref{launcher} +is used as a control process. We call such a process a {\bf +control server}. In contrast, we call a server for computation an {\bf +engine}. In this case the control server and the engine runs on the +same machine and it is easy to manipulate the engine, especially to +send a signal from the control server. A control server is also an +OpenXM stackmachine and it accepts {\tt SM\_control\_*} commands +to send signals to a server or to terminate a server. + +\subsection{Resetting a connection} + +By using the control channel a client can send a signal to an engine +at any time. However, I/O operations are usually buffered and several +additional operations on buffers after sending a signal is necessary +to reset connections safely. Here a safe resetting means the +following: + +\begin{enumerate} +\item A sending of an {\tt OX} message must be completed. + +As an {\tt OX} message is sent as a combination of several {\tt CMO} +data, a global exit without sending all the data confuses the +subsequent communication. + +\item After restarting a server, a request from a client +must correctly corresponds to the response from the server. + +An incorrect correspondence occurs if some data remain on the stream +after restarting a server. +\end{enumerate} + +{\tt SM\_control\_reset\_connection} is an {\tt SM} command to +initiate a safe resetting of a connection. We show the action of +a server and a client from the initiation to the completion of +a resetting. + +\centerline{\fbox{client}} + +\begin{enumerate} +\item The client sends {\tt SM\_control\_reset\_connection} to the +control server. +\item The client enters the resetting state. it skips all {\tt +OX} messages from the engine until it receives {\tt OX\_SYNC\_BALL}. +\item After receiving {\tt OX\_SYNC\_BALL} the client sends +{\tt OX\_SYNC\_BALL} to the engine and returns to the usual state. +\end{enumerate} + +\centerline{\fbox{engine}} + +\begin{enumerate} +\item After receiving {\tt SIGUSR1} from the control server, +the engine enters the resetting state. +\item If an {\tt OX} message is being sent or received, then +the engine completes it. This does not block because +the client reads and skips {\tt OX} messages soon after sending +{\tt SM\_control\_reset\_connection}. +\item The engine sends {\tt OX\_SYNC\_BALL} to the client. +\item The engine skips all {\tt OX} messages from the engine until it +receives {\tt OX\_SYNC\_BALL}. +\item After receiving {\tt OX\_SYNC\_BALL} the engine returns to the +usual state. +\end{enumerate} + +{\tt OX\_SYNC\_BALL} means an end mark of the data remaining in the +I/O streams. After reading it it is assured that the stream is empty +and that a request from a client correctly corresponds to the response +from the server. We note that we don't have to associate +{\tt OX\_SYNC\_BALL} with +any special action to be executed by the server because it is +assured that the peer is in the resetting state when one receives +{\tt OX\_SYNC\_BALL}. + +\subsection{Debugging supports} +To help debugging on the server, various supports are possible. If +servers are executed on X window system, then the control server can +attach an {\tt xterm} to the standard outputs of the engine to display +diagnostic messages from the engine. +Furthermore, if the engine provides an interface to input commands, +then debugging of user defined programs will be +possible. For example {\tt ox\_asir}, which is +the OpenXM server of {\tt Risa/Asir}, can pop up a window to input +debug commands and the debugging similar to that on usual terminals is possible. +One can also send {\tt SIGINT} by using {\tt SM\_control\_intr} +and it provides a similar functionality to entering the debugging +mode from a keyboard interruption.