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| author | doccvs <doccvs@ae88bc3d-4319-0410-8dbf-d08b4c9d3795> | 2000-03-24 18:10:22 +0000 |
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| committer | doccvs <doccvs@ae88bc3d-4319-0410-8dbf-d08b4c9d3795> | 2000-03-24 18:10:22 +0000 |
| commit | 08b6fe5fcf67621bd4c498bbb3ba269d01144235 (patch) | |
| tree | 05eafd923d4e3a72a01da114459f8cf8c14d42bf | |
| parent | 9d25a9cab3af5b7f3a2974aa1ef1c07a72cb5ac7 (diff) | |
| download | ATCD-08b6fe5fcf67621bd4c498bbb3ba269d01144235.tar.gz | |
2000-03-24 Priyanka Gontla <pgontla@doc.ece.uci.edu>
| -rw-r--r-- | TAO/docs/tutorials/Quoter/Simple/Persistent/persistent.html | 263 |
1 files changed, 263 insertions, 0 deletions
diff --git a/TAO/docs/tutorials/Quoter/Simple/Persistent/persistent.html b/TAO/docs/tutorials/Quoter/Simple/Persistent/persistent.html new file mode 100644 index 00000000000..677d92f1f08 --- /dev/null +++ b/TAO/docs/tutorials/Quoter/Simple/Persistent/persistent.html @@ -0,0 +1,263 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> +<html> + <head> + <title>Persistent Objects</title> + <!-- $Id$ --> + <META HTTP-EQUIV="Refresh" CONTENT="1; URL=../persistent.html"> + </head> + + <BODY text = "#000000" + link="#000fff" + vlink="#ff0f0f" + bgcolor="#ffffff"> + + <h1>Introduction - Improving the Server</h1> + + <P>In this section, we will improve the <a href = ../server.cpp> + simple server</a> which we have developed before. We will use POA policies + to create a persistent object reference. </P> + <P> + The characteristics of a POA are controlled via POA policies. These POA + policies are specified when the POA is created. POA policies have the + same form: their values are specified using an enumerated type. One such + policy is the LifeSpanPolicy.The LifespanPolicyValue can be Transient or + Persistent. + </P> + + <P> CORBA objects that can live irrespective of any particular process in + which they are created or activated are called Persistent Objects. + The shorter-lived objects whose life time is bounded by the lifetime of + the POA in which they are created are called Transient Objects. + </P> + <P> The standard life span policy for the RootPOA is Transient. This means + that any application that needs to support persistent objects must create + at least another POA with the Persistent life span policy. + </P> + <P> Lets create a new child POA with the RootPOA as its + parent. We will create two policies for this childPOA. One policy is the + Life Span Policy which we will set to be Persistent. The second policy + is the Id Assignment Policy. + </P> + <P> A POA identifies its object by an object identifier, specified + using the ObjectId type, defined in the PortableServer module. Within the + scope of a POA, all Object IDs must be unique. An application can either + supply its own ObjectID or have the POA create object identifiers for it. + This Object identification is controlled by the IdAssignmentPolicy. If + the policy value is set to be <CODE>USER_ID</CODE>, the application has + the choice. Else, if this policy value is set to be + <CODE>SYSTEM_ID</CODE>, the RootPOA creates the ObjectIDs. Lets give our + application a choice for the creation of its Object's IDs. + </P> + <P>For more about POA and its policies, please refer Advanced CORBA + Programming with C++ by Henning and Vinoski. There are many examples in + <CODE>$TAO_ROOT/examples/POA/</CODE> that show how to use the other + policies in the POA. + </P> + <H3> Child POA Creation </H3> + + As before we first initialize the ORB, get a reference to the Root POA. + <PRE> + CORBA::ORB_var orb = CORBA::ORB_init (argc, argv); + CORBA::Object_var poa_object = + orb->resolve_initial_references ("RootPOA"); + PortableServer::POA_var poa = + PortableServer::POA::_narrow (poa_object.in ()); + </PRE> + + Next get the POAManager of the RootPOA and activate it. + <PRE> + PortableServer::POAManager_var poa_manager = + poa->the_POAManager (); + + poa_manager->activate (); + </PRE> + + <P>The policies of a POA are stored in a sequence. Lets first create a + CORBA::PolicyList sequence. Since we are creating two policies, lets + initialize its length to be 2. + </P> + <PRE> + CORBA::PolicyList polices; + policies.length (2); + </PRE> + <P> Now to create a LifeSpanPolicy Object and an IdAssignmentpolicy Object. + We use the <CODE>create_lifespan_policy</CODE> operation of the Root POA + to create a LifespanPolicy object.Since we want the POA to be + <CODE>PERSISTENT</CODE>, we pass the same as its value. For creating the + IdAssignmentPolicy object, we use the + <CODE>create_id_assignment_policy</CODE> operation of the Root POA and + pass <CODE>USER_ID</CODE> as its value. + </P> + <PRE> + // Create a PERSISTENT LifespanPolicy object + PortableServer::LifespanPolicy_var lifespan = + poa->create_lifespan_policy (PortableServer::PERSISTENT); + + // Create a USER_ID IdAssignmentPolicy object + PortableServer::IdAssignmentPolicy_var idassignment = + poa->create_id_assignment_policy (PortableServer::USER_ID); + </PRE> + <P>Now that we have created the respective objects, we copy our reference + to these objects into the policy list. + </P> + <PRE> + policies[0] = + PortableServer::IdAssignmentPolicy::_duplicate (idassignment); + policies[1] = + PortableServer::LifespanPolicy::_duplicate (lifespan); + </PRE> + <P> Now lets come to the actual creation of the child POA. We create a POA + by invoking the <CODE>create_POA</CODE> on the POA for which we want to + create the new child POA. Here, in our case, the RootPOA is the parent + POA and the child POA is its child. So, we will invoke the + <CODE>create_POA</CODE> operation on the RootPOA. + </P> + <PRE> + PortableServer::POA_var child_poa = + poa->create_POA ("childPOA", + poa_manager.in (), + policies); + </PRE> + <P>The values which we pass to this <CODE>create_POA</CODE> operation are + the name of the child POA, the POAManager of the child POA and the + <CODE>CORBA::PolicyList</CODE>. Here, we have the POAManager of its + parent, i.e. the RootPOAs POAManager, as the childPOA's POAManager. + </P> + <P> Finally, we can now destroy the life span policy and id assignment + policy objects since they are no longer needed. The + <CODE>create_POA</CODE> operation will make a copy of the objects in the + policy list. And the newly created POA will refer to the copies of the + objects passed to the <CODE>create_POA</CODE>. + </P> + <PRE> + idassignment->destroy (); + lifespan->destroy (); + </PRE> + <H3> Activating Objects in the child POA </H3> + <P>Now that we have created a new POA, lets use this POA to activate the + stock objects. The first step would be to create an instance of the + stock factory implementation. + <PRE> + // Create a servant of class Quoter_Stock_Factory_i + Quoter_Stock_Factory_i stock_factory_i; + </PRE> + <P>Now, we have to activate it. One of the most easy ways to + activate an object is to use the POA object activation operations. One + of the two operations is the <CODE>activate_object_with_id ()</CODE> + operation. This operation has two input parameters: the Objects Id and + the servant to incarnate the object. So, for this, we have to first + get the ObjectId. + </P> + <PRE> + PortableServer::ObjectId_var oid = + PortableServer::string_to_ObjectId ("Stock_Factory"); + </PRE> + <P>Here, we have used the <CODE>string_to_ObjectId</CODE> helper function + to convert the string "Stock_Factory" into an ObjectId. Now we can + activate the "Stock_Factory" object. + </P> + <PRE> + child_poa->activate_object_with_id (oid.in (), + &stock_factory_i); + </PRE> + <P>This operation doesnt return the object reference of the new object. One + way to get the object reference is to invoke the + <CODE>id_to_reference</CODE> operation on the POA after activating the + object. + </P> + <PRE> + CORBA::Object_var stock_factory = + child_poa->id_to_reference (oid.in ()); + </PRE> + <P>Next, as before, we convert the object reference into an IOR string so + that the client can use it. + </P> + <PRE> + CORBA::String_var ior = orb->object_to_string (stock_factory.in ()); + std::cout << ior.in () << std::endl; + </PRE> + <P>As we know already, the final step before a client's request can + get processed would be to run the ORB event loop.And then to destroy + the POA waiting until the destruction terminates. + </P> + <PRE> + orb->run (); + + // Destroy the POA + poa->destroy (1,1); + orb->destroy (); + </PRE> + <H3>Exercise</H3> + + Modify the <a href=../Simple/Server/server.cpp>server.cpp</a> in the simple + server to create the persistent child POA. + You can use the same + <a href=../Quoter.idl>Quoter.idl</a> + <a href=../Server/Stock_i.h>Stock_i.h</a> + <a href=../Server/Stock_i.cpp>Stcok_i.cpp</a> + <a href=../Server/Stock_Factory_i.h>Stock_Factory_i.h</a> + <a href=../Server/Stock_Factory_i.cpp>Stock_Factory_i.cpp</a> + You can use this <a href=Makefile>Makefile</a>. + <H3>Solution</H3> + Compare your server.cpp with <a href = server.cpp>server.cpp</a> file. + + <H3>Testing</H3> + You can use the <a href=../Client/client.cpp>client.cpp</a> to check + the results, as follows: + <PRE> + $ ./server -ORBENDPOINT iiop://doc.ece.uci.edu:12345 > server.ref & + [1] 6933 + </PRE> + <P>What we did here is telling the server ORB to listen for requests on the + interface specified by the endpoint.For example, for the IIOP protocol, + the endpoint information contains an Internet domain name or IP address + and a TCP port number, basically in + <CODE>iiop://hostname:port</CODE> format. + </P> + <P> Now, for the client part. + </P> + <PRE> + $ ./client file://server.ref MSFT RHAT + </PRE> + <P>For testing the persistency of the POA, lets kill the server. Then + direct the object reference into a new foo.ref. + </P> + <PRE> + $ kill %1 + $ ./server -ORBENDPOINT iiop://doc.ece.uci.edu:12345 > foo.ref & + [2] 6941 + </PRE> + <P>If we run the client again, we must get the result from the server + as before. + </P> + <PRE> + $ ./client file://server.ref MSFT RHAT + </PRE> + <P>What happens if we donot tell the server to listen from the same port? + Lets compile and run as we did in our simple server. + </P> + <PRE> + $ ./server > server.ref & + [1] 23897 + $ ./client file://server.ref MSFT RHAT + The price of a stock in "RedHat, Inc." is $210 + The price of a stock in "Microsoft, Inc." is $91 + $ kill %1 + $ ./server > foo.ref & + [2] 23908 + $ ./client file://server.ref MSFT RHAT + CORBA exception raised!TRANSIENT (IDL:omg.org/CORBA/TRANSIENT:1.0) + </PRE> + <P> A CORBA exception is raised saying that the object is a Transient one. + Since if the port is not specified, the ORB will listen to a random empty + port each time a new request arrives. Thsi results in the object being + transient. + </P> + <hr> + <address><a href="mailto:pgontla@ece.uci.edu">Priyanka Gontla</a></address> +<!-- Created: Wed Mar 1 20:29:59 PST 2000 --> +<!-- hhmts start --> +Last modified: Fri Mar 24 10:09:47 PST 2000 +<!-- hhmts end --> + </body> +</html> |