[BACK]Return to session-management.tex CVS log [TXT][DIR] Up to [local] / OpenXM / doc / issac2000

Diff for /OpenXM/doc/issac2000/session-management.tex between version 1.7 and 1.12

version 1.7, 2000/01/15 03:46:27 version 1.12, 2000/01/17 07:15:52
Line 1 
Line 1 
 % $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.6 2000/01/15 00:20:46 takayama Exp $  % $OpenXM: OpenXM/doc/issac2000/session-management.tex,v 1.11 2000/01/17 06:10:41 noro Exp $
   
 \section{Session Management}  \section{Session Management}
 \label{secsession}  \label{secsession}
Line 6 
Line 6 
 %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.
   
 In this section we show the realization of control integration in  In this section we explain our control integration in
 OpenXM.  In OpenXM it is assumed that various clients and servers  OpenXM.  We assume that various clients and servers
 establish connections dynamically and communicate to each  establish connections dynamically and communicate to each
 other. Therefore it is necessary to unify the communication interface  other. Therefore it is necessary to give a dynamical and unified
 and the method of communication establishment.  Besides, interruption  method to start servers and to establish connections.
 of an execution and debugging are common operations when we use  In addition to that, interruption of executions and
 programming systems. OpenXM provides a method to realize them for  debugging facilities
 distributed computation.  are necessary for interactive distributed computation.
   
 \subsection{Interface of servers}  %\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 coincide 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.
   
 A server has additional I/O streams for exchanging data between  \subsection{Invocation of servers}
 a client and itself other than ones for diagnostic  \label{launcher}
 messages. As the streams are for binary data,  
   An application called {\it launcher} is provided to start servers
   and to establish connections as follows.
   
   \begin{enumerate}
   \item A launcher is invoked from a client.
   When the launcher is invoked, the client
   informs the launcher of a port number for TCP/IP connection
   and the name of a server.
   \item The launcher and the client establish a connection with the
   specified port number. One time password may be used to prevent
   launcher spoofing.
   \item The launcher creates a process and executes the server after
   setting the data channel appropriately.
   \end{enumerate}
   
   After finishing the above task as a launcher, the launcher process
   acts as a control server and controls the server process created by
   itself. As to the control server see Section \ref{control}.
   
   As the data channel is used to exchange binary data,
 the byte order conversion is necessary when a  the byte order conversion is necessary when a
 client and a server have different byte orders. It is determined by  client and a server have different byte orders. It is determined by
 exchanging the preferable byte order of each peer. If the preference  exchanging the preferable byte order of each peer. If the preference
Line 31  order. Nevertheless it is necessary to negotiate the b
Line 65  order. Nevertheless it is necessary to negotiate the b
 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.
   
 \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}  
   
 After finishing the above 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}  \subsection{Control server}
 \label{control}  \label{control}
 When we use a mathematical software, an execution time or necessary  In OpenXM we adopted the following simple and robust method to
 storage is often unknown in advance. Therefore it is desirable  control servers.
 to be able to abort an execution and to start another execution.  
 In 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 controlling 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. The launcher introduced in Section \ref{launcher}  server. The launcher introduced in Section \ref{launcher}
 is used as a control process. We call such a process a {\bf  is used as a control process. We call such a process a {\it
 control server}. In contrast, we call a server for computation an {\bf  control server}. In contrast, we call a server for computation an {\it
 engine}. In this case the control server and the engine runs on the  engine}. As the control server and the engine runs on the
 same machine and it is easy to manipulate the engine, especially to  same machine, 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 it accepts {\tt SM\_control\_*} commands  OpenXM stack machine and it accepts {\tt SM\_control\_*} commands
 to send signals to a server or to terminate a server.  to send signals to a server or to terminate a server.
   
 \subsection{Resetting a connection}  \subsection{Resetting an engine}
   
 By using the control channel a client can send a signal to an engine  A client can send a signal to an engine by using the control channel
 at any time. However, I/O operations are usually buffered and several  at any time. However, I/O operations are usually buffered,
 additional operations on buffers after sending a signal is necessary  which may cause troubles.
 to reset connections safely. Here a safe resetting means the  To reset an engine safely the following are required.
 following:  
   
 \begin{enumerate}  \begin{enumerate}
 \item A sending of an {\tt OX} message must be completed.  \item Any OX message must be a synchronized object in the sense of Java.
   
 As an {\tt OX} message is sent as a combination of several {\tt CMO}  As an OX message is sent as a combination of several {\tt CMO}
 data, a global exit without sending all the data confuses the  data, a global exit without sending all may generate broken data.
 subsequent communication.  
   
 \item After restarting a server, a request from a client  \item After restarting an engine, a request from a client
 must correctly corresponds to the response from the server.  must correctly corresponds to the response from the engine.
   
 An incorrect correspondence occurs if some data remain on the stream  An incorrect correspondence occurs if some data remain on the stream
 after restarting a server.  after restarting an engine.
 \end{enumerate}  \end{enumerate}
   
 {\tt SM\_control\_reset\_connection} is an {\tt SM} command to  {\tt SM\_control\_reset\_connection} is a stack machine command to
 initiate a safe resetting of a connection. We show the action of  initiate a safe resetting of an engine.
 a server and a client from the initiation to the completion of  The control server sends {\tt SIGUSR1} to the engine if it receives
 a resetting.  {\tt SM\_control\_reset\_connection} from the client.
   Under the OpenXM reset protocol an engine and a client act as follows.
   
 \centerline{\fbox{client}}  \vskip 2mm
   \noindent
   {\it Client side}
 \begin{enumerate}  \begin{enumerate}
 \item The client sends {\tt SM\_control\_reset\_connection} to the  \item After sending {\tt SM\_control\_reset\_connection} to the
 control server. The control server sends {\tt SIGUSR1} to the engine.  control server, 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 receives {\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}
   
 \centerline{\fbox{engine}}  \noindent
   {\it Engine side}
 \begin{enumerate}  \begin{enumerate}
 \item After receiving {\tt SIGUSR1} from the control server,  \item
   After receiving {\tt SIGUSR1} from the control server,
 the engine enters the resetting state.  the engine enters the resetting state.
 \item If an {\tt OX} message is being sent or received, then  The engine sends {\tt OX\_SYNC\_BALL} to the client.
 the engine completes it. This does not block because  The operation does not block because
 the client reads and skips {\tt OX} messages soon after sending  the client is now in the resetting state.
 {\tt SM\_control\_reset\_connection}.  \item The engine skips all OX messages from the engine until it
 \item The engine sends {\tt OX\_SYNC\_BALL} to the client.  receives {\tt OX\_SYNC\_BALL}. After receiving {\tt OX\_SYNC\_BALL}
 \item The engine skips all {\tt OX} messages from the engine until it  the engine returns to the usual state.
 receives {\tt OX\_SYNC\_BALL}.  
 \item After receiving {\tt OX\_SYNC\_BALL} the engine returns to the  
 usual state.  
 \end{enumerate}  \end{enumerate}
   
 {\tt OX\_SYNC\_BALL} means an end mark of the data remaining in the  \begin{figure}[htbp]
 I/O streams. After reading it it is assured that each stream is empty  \epsfxsize=8.5cm
   \epsffile{reset.eps}
   \caption{OpenXM reset procedure}
   \label{reset}
   \end{figure}
   
   Figure \ref{reset} illustrates the flow of data.
   {\tt OX\_SYNC\_BALL} is used to mark the end of data remaining in the
   I/O streams. After reading it, it is assured that each stream is empty
 and that the subsequent request from a client correctly  and that the subsequent request from a client correctly
 corresponds to the response from the server.  corresponds to the response from the engine.
 We note that we don't have to associate {\tt OX\_SYNC\_BALL} with  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  any special action to be executed by the engine because it is
 assured that the peer is in the resetting state when one receives  assured that the engine is in the resetting state when it has received
 {\tt OX\_SYNC\_BALL}.  {\tt OX\_SYNC\_BALL}.
   
 \subsection{Debugging supports}  \subsection{Debugging facilities}
 To help debugging on the server, various supports are possible. If  Debugging is sometimes very hard for distributed computations.
 servers are executed on X window system, then the control server can  We provide two methods to help debugging on X window system:
 attach an {\tt xterm} to the standard outputs of the engine to display  1. the diagnostic messages from the engine are displayed in a {\tt xterm}
 diagnostic messages from the engine.  window;
 Furthermore, if the engine provides an interface to input commands,  2. the engine can pop up a window to input debug commands.
 then debugging of user defined programs will be  For example {\tt ox\_asir}, which is
 possible. For example {\tt ox\_asir}, which is  the OpenXM server of Risa/Asir, can pop up a window to input
 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.  debug commands and the debugging similar to that on usual terminals is possible.
 One can also send {\tt SIGINT} by using {\tt SM\_control\_to\_debug\_mode}  One can also send {\tt SIGINT} by using {\tt SM\_control\_to\_debug\_mode}
 and it provides a similar functionality to entering the debugging  and it provides a similar functionality to entering the debugging
Legend:
Removed from v.1.7  
changed lines
  Added in v.1.12
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>