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version 1.3, 2000/01/04 09:14:14 version 1.5, 2000/01/11 05:35:48
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 % $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.2 2000/01/02 07:32:12 takayama Exp $  % $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.4 2000/01/07 06:27:55 noro Exp $
   
 \section{Session Management}  \section{Session Management}
   \label{secsession}
 %MEMO: key words:  %MEMO: key words:
 %Security (ssh PAM), initial negotiation of byte order,  %Security (ssh PAM), initial negotiation of byte order,
 %mathcap, interruption, debugging window, etc.  %mathcap, interruption, debugging window, etc.
Line 31  A server reads data from the stream {\bf 3} and writes
Line 31  A server reads data from the stream {\bf 3} and writes
 stream {\bf 4}. The streams {\bf 1} and {\bf 2} are provided for  stream {\bf 4}. The streams {\bf 1} and {\bf 2} are provided for
 diagnostic messages from the server.  As {\bf 3} and {\bf 4} are  diagnostic messages from the server.  As {\bf 3} and {\bf 4} are
 streams for binary data, the byte order conversion is necessary when a  streams for binary data, the byte order conversion is necessary when a
 client and a server have different byte orders. There are several  client and a server have different byte orders. Various
 methods to treat it and we adopted the following scheme.  methods are possible to treat it and we adopted the following scheme.
   
 \begin{itemize}  \begin{itemize}
 \item A server writes 1 byte representing the preferable byte order.  \item A server writes 1 byte representing the preferable byte order.
 \item After reading the byte, a client writes 1 byte representing the  \item After reading the byte, a client writes 1 byte representing the
 preferable byte order.  preferable byte order.
 \item On each side, if the preference coicides with each other then  \item On each side, if the preference coincides with each other then
 the byte order is used. Otherwise the network byte order is used.  the byte order is used. Otherwise the network byte order is used.
 \end{itemize}  \end{itemize}
   
 This implies that all servers and clients can handle the network byte  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  order. Nevertheless it is necessary to negotiate the byte order to
 skip the byte order conversion because its cost is often dominant over  skip the byte order conversion because its cost is often dominant over
 fast networks.  fast networks.
Line 60  the launcher as follows.
Line 61  the launcher as follows.
 \item A launcher is invoked from a client or by hand.  \item A launcher is invoked from a client or by hand.
 When the launcher is invoked, a port number for TCP/IP connection  When the launcher is invoked, a port number for TCP/IP connection
 and the name of a server should be informed.  and the name of a server should be informed.
 \item The launcher and the client establish a conection with the  \item The launcher and the client establish a connection with the
 specified port number.  specified port number.
 \item The launcher create a process and execute the server after  \item The launcher create a process and execute the server after
 setting the streams {\bf 3} and {\bf 4} appropriately.  setting the streams {\bf 3} and {\bf 4} appropriately.
Line 78  When we use a mathematical software, an execution time
Line 79  When we use a mathematical software, an execution time
 storage is often unknown in advance. Therefore it is desirable  storage is often unknown in advance. Therefore it is desirable
 to be able to abort an execution and to start another execution.  to be able to abort an execution and to start another execution.
 On a usual session on UNIX it is done by an interruption from a keyboard.  On a usual session on UNIX it is done by an interruption from a keyboard.
 Internally it is realized by an exeption processing initiated by  Internally it is realized by an exception processing initiated by
 a {\bf signal}, but it is not easy to send a signal to a server.  a {\bf signal}, but it is not easy to send a signal to a server.
 Especially if a server and a client run on different machines,  Especially if a server and a client run on different machines,
 the client cannot send a signal to the server directly.  the client cannot send a signal to the server directly.
Line 88  system dependent and lack robustness.
Line 89  system dependent and lack robustness.
 On OpenXM we adopted the following simple and robust method.  On OpenXM we adopted the following simple and robust method.
   
 An OpenXM server has logically two I/O channels: one for exchanging  An OpenXM server has logically two I/O channels: one for exchanging
 data for computations and the other for controling computations. The  data for computations and the other for controlling computations. The
 control channel is used to send commands to control execution on the  control channel is used to send commands to control execution on the
 server. There are several ways of implementing the control channel.  server. There are several ways of implementing the control channel.
 Among them it is common to use the launcher introduced in Section  Among them it is common to use the launcher introduced in Section
 \ref{launcher} as a control process. We call such a process a {\bf  \ref{launcher} as a control process. We call such a process a {\bf
 control server}. In contrast, we call a server for computation an {\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  engine}. In this case the control server and the engine runs on the
 same machine and it is easy to maniputalate the engine, especially to  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  send a signal from the control server. A control server is also an
 OpenXM stackmachine and the following {\tt SM} commands are provided.  OpenXM stackmachine and the following {\tt SM} commands are provided.
   
Line 144  a resetting.
Line 145  a resetting.
 \item The client sends {\tt SM\_control\_reset\_connection} to the  \item The client sends {\tt SM\_control\_reset\_connection} to the
 control server.  control server.
 \item The client enters the resetting state. it skips all {\tt  \item The client enters the resetting state. it skips all {\tt
 OX} messages from the engine until it recieves {\tt OX\_SYNC\_BALL}.  OX} messages from the engine until it receives {\tt OX\_SYNC\_BALL}.
 \item After receiving {\tt OX\_SYNC\_BALL} the client sends  \item After receiving {\tt OX\_SYNC\_BALL} the client sends
 {\tt OX\_SYNC\_BALL} to the engine and returns to the usual state.  {\tt OX\_SYNC\_BALL} to the engine and returns to the usual state.
 \end{enumerate}  \end{enumerate}
Line 161  the client reads and skips {\tt OX} messages soon afte
Line 162  the client reads and skips {\tt OX} messages soon afte
 {\tt SM\_control\_reset\_connection}.  {\tt SM\_control\_reset\_connection}.
 \item The engine sends {\tt OX\_SYNC\_BALL} to the client.  \item The engine sends {\tt OX\_SYNC\_BALL} to the client.
 \item The engine skips all {\tt OX} messages from the engine until it  \item The engine skips all {\tt OX} messages from the engine until it
 recieves {\tt OX\_SYNC\_BALL}.  receives {\tt OX\_SYNC\_BALL}.
 \item After receiving {\tt OX\_SYNC\_BALL} the engine returns to the  \item After receiving {\tt OX\_SYNC\_BALL} the engine returns to the
 usual state.  usual state.
 \end{enumerate}  \end{enumerate}
Line 188  OX\_SYNC\_BALL} must initiate an engine into entering 
Line 189  OX\_SYNC\_BALL} must initiate an engine into entering 
 state, and it makes the resetting scheme complicated and it may  state, and it makes the resetting scheme complicated and it may
 introduce unexpected bugs. For example, if a client sends {\tt  introduce unexpected bugs. For example, if a client sends {\tt
 OX\_SYNC\_BALL} without waiting {\tt OX\_SYNC\_BALL} from the engine,  OX\_SYNC\_BALL} without waiting {\tt OX\_SYNC\_BALL} from the engine,
 then it is possible that the engine recieves it before the arrival of  then it is possible that the engine receives it before the arrival of
 the signal. We note that we really encountered serious bugs caused  the signal. We note that we really encountered serious bugs caused
 by such an inappropriate protocol before reaching the final specicication.  by such an inappropriate protocol before reaching the final specification.
   
 \subsection{Debugging}  \subsection{Debugging supports}
 An OpenXM server may allow definition and execution of functions  An OpenXM server may allow definition and execution of functions
 written in the user language proper to the server.  To help debugging  written in the user language proper to the server.  To help debugging
 such functions on the server, various supports are possible. If  such functions on the server, various supports are possible. If
 servers are executed on X window system, then the control server can  servers are executed on X window system, then the control server can
 attach an {\tt xterm} to the standard outputs of the engine, which  attach an {\tt xterm} to the standard outputs of the engine, which
 makes it possible to display messages from the engine. Furthermore, if  makes it possible to display messages from the engine. Furthermore, if
 the engine provides an inteface to input commands which directly  the engine provides an interface to input commands which directly
 controls the engine, then debugging of user define programs will be  controls the engine, then debugging of user define programs will be
 possible. For example {\tt Risa/Asir} provides a function {\tt  possible. For example {\tt Risa/Asir} provides a function {\tt
 debug()} to debug user defined functions. {\tt ox\_asir}, which is  debug()} to debug user defined functions. {\tt ox\_asir}, which is
Line 208  debug commands when {\tt debug()} is executed on the s
Line 209  debug commands when {\tt debug()} is executed on the s
 As the responses to the commands are displayed on the {\tt xterm},  As the responses to the commands are displayed on the {\tt xterm},
 the debugging similar to that on usual terminals is possible.  the debugging similar to that on usual terminals is possible.
 Moreover one can send {\tt SIGINT} by using {\tt SM\_control\_intr}  Moreover one can send {\tt SIGINT} by using {\tt SM\_control\_intr}
 and it provides a similar functinality to entering the debugging  and it provides a similar functionality to entering the debugging
 mode from a keyboard interruption.  mode from a keyboard interruption.
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