TAO/docs/tutorials/Quoter/Simple/Impl-Repo/index.html

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  13     <h3>Implementation Repository</h3>
  14     <P> In the previous example, the client must contact the server
  15       at least once. If the server has been moved to a different host or
  16       port, or if the server is down, binding between the client and
  17       the server fails. Indirect binding through an external location
  18       broker like the Implementation Repository solves this problem.
  19     </P>
  20     <P>An implementation repository maintains a data structure known
  21       as a server table to keep track of the servers. It maintains a
  22       registry of known servers, records which server is currently
  23       running on which host and at which port number, and starts
  24       servers on demand if they are registered to do so.
  25     </P>
  26     <P> When a server
  27       creates a persistent reference, it sets the address and port
  28       number in the profile body of the IOR to point at the
  29       implementation repository that is responsible for the server.
  30       When a client uses this IOR, it gets connected to the
  31       implementation repository, provided the implementation
  32       repository is not down. The repository decodes this IOR and uses
  33       the POA name from the object key to index into its server
  34       table. The repository replies with the current addressing
  35       information of the actual server. The client now sends the
  36       request to the actual server.
  37     </P>
  38     <P>In this example, let's proceed to modify our previous stock
  39       factory example to support indirect binding through an
  40       implementation repository.
  41     </P>
  42     <P>The only thing we have to do for this is to register our
  43       childPOA with the implementation repository.
  44     </P>
  45     <PRE>
  46        orb->_tao_add_to_IOR_table ("childPOA", stock_factory.in ());
  47     </PRE>
  48     <P> Then, we stringify all the object references as usual and
  49       print them out.
  50     </P>
  51     <PRE>
  52        CORBA::String_var ior = orb->object_to_string (stock_factory.in ());
  53     </PRE>
  54     <H3>Exercise</H3>
  55     Modify the <a href=../Server/server.cpp>server.cpp</a> in the simple
  56     server to  create the persistent child POA.
  57     You can use the same
  58     <a href=../Quoter.idl>Quoter.idl</a>
  59     <a href=../Server/Stock_i.h>Stock_i.h</a>
  60     <a href=../Server/Stock_i.cpp>Stock_i.cpp</a>
  61     <a href=../Server/Stock_Factory_i.h>Stock_Factory_i.h</a>
  62     <a href=../Server/Stock_Factory_i.cpp>Stock_Factory_i.cpp</a>
  63     <a href=../Client/client.cpp>Client.cpp</a>
  64     You can use this <a href=Quoter_Simple_Impl_Repo_Server.mpc>MPC file</a>.
  65     <H3>Solution</H3>
  66     Compare your server.cpp with <a href = server.cpp>server.cpp</a> file.
  67
  68     <H3>Testing</H3>
  69     <P>To test your changes, you need to run four programs. The first
  70       step is to start up the Implementation Repository provided
  71       with TAO. The Implementation Repository is split into one locator at least
  72       one activator. The locator provides the interface visible
  73       to the application intending to use the repository (in our case,
  74       the client), while the activators do the real work of activating
  75       and maintaining servers.
  76     </P>
  77
  78     <P>First, we start the locator. We need to dump the IOR of the ImplRepo_Service to a file,
  79       so that both the activator and the client can find the locator.
  80     </P>
  81     <PRE>
  82        $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator -o implrepo.ior -d 0 -ORBobjrefstyle URL &
  83     </PRE>
  84
  85     <P>Second, we start the activator, pointing it to the locator's IOR file.
  86     </P>
  87     <PRE>
  88        $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_activator -ORBInitRef ImplRepoService=file://implrepo.ior
  89
  90           ImR Activator: Starting doc.ece.uci.edu
  91           ImR Activator: Registered with ImR.
  92     </PRE>
  93
  94     <P> Next, we need to register our server with the implementation
  95       repository. We can use the
  96       <CODE>$TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator</CODE>
  97       application provided with TAO to add our server to the server
  98       database in the implementation repository.
  99     </P>
 100     <PRE>
 101        $ $TAO_ROOT/orbsvcs/ImplRepo_Service/tao_imr_locator -ORBInitRef
 102          ImplRepoService=file://implrepo.ior add childPOA -c
 103          "./server -ORBUseIMR 1 -ORBobjrefstyle URL -ORBInitRef
 104          ImplRepoService=file://implrepo.ior"
 105
 106           Successfully registered server <childPOA>
 107     </PRE>
 108     <p> On Windows platforms, use this command instead to register the server
 109       in the implementation repository
 110     </p>
 111     <PRE>
 112     $ACE_ROOT/bin/tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior
 113     add childPOA -c "./server -ORBUseIMR 1 -ORBobjrefstyle URL
 114     -ORBInitRef ImplRepoService=file://implrepo.ior"
 115     </PRE>
 116     <P> We specify the <CODE>-ORBInitRef</CODE> option to use the IOR in
 117       the <CODE>implrepo.ior</CODE> file and the <CODE>-ORBUseIMR</CODE>
 118       option to tell the server to use the IMR for notification of its
 119       startup and shutdown.
 120     </P>
 121     <P>The next step is to generate a simple IOR for our server
 122       to be used with the IMR, using the
 123       <CODE>ior</CODE> option, and write it to <CODE>stock_factory.ior</CODE>.
 124
 125     </P>
 126     <PRE>
 127        $tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior ior
 128        childPOA -f stock_factory.ior
 129
 130          corbaloc:iiop:1.1@doc.ece.uci.edu:2690/childPOA
 131     </PRE>
 132     <P> From now, the implementation repository is all set to keep
 133       track of our server and do the needful on a method invocation
 134       on our server.
 135     </P>
 136     <P> Now, execute the client as usual.
 137     </P>
 138     <PRE>
 139        ./client file://stock_factory.ior MSFT RHAT
 140
 141        The price of a stock in "Microsoft, Inc." is $91
 142        The price of a stock in "RedHat, Inc." is $210
 143     </PRE>
 144     <P> For testing the persistency of the POA, let's shut down the
 145       server and then run the client.
 146     </P>
 147     <PRE>
 148        $tao_imr -ORBInitRef ImplRepoService=file://implrepo.ior
 149        shutdown childPOA
 150
 151          Successfully shutdown server <childPOA>
 152
 153        ./client file://stock_factory.ior MSFT RHAT
 154
 155          The price of a stock in "RedHat, Inc." is $210
 156          The price of a stock in "Microsoft, Inc." is $91
 157     </PRE>
 158     <H3>More Reading</H3>
 159     <P>More information on Implementation Repository is
 160      <A  HREF="../../../../../docs/implrepo/index.html">here</A>.
 161     </P>
 162       <P>The <A HREF="http://www.triodia.com/staff/michi-henning.html">Henning</A> and <A HREF="http://www.iona.com/hyplan/vinoski/">Vinoski</A>
 163       <A HREF="http://www.iona.com/hyplan/vinoski/#book">CORBA book</A> discusses POA policies in detail.  Likewise,
 164       the Schmidt and Vinoski
 165       <A HREF="http://www.cs.wustl.edu/~schmidt/report-doc.html">columns</A> in C++ Report also include several articles about the POA.  Finally,
 166       the <A HREF="http://www.dre.vanderbilt.edu/~schmidt/TAO.html">TAO</A>
 167       distribution includes <A HREF="../../../../../examples/POA">examples</A> that illustrate how
 168       to use the POA policies.
 169     </P>
 170     <hr>
 171     <address><a href="mailto:pgontla@ece.uci.edu">Priyanka Gontla</a></address>
 172 <!-- Created: Wed Mar 29 17:35:30 PST 2000 -->
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 174 Last modified: Sat May 19 17:19:07 CDT 2001
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