Corba and Multi-Threading

• The last three or four columns that Doug Schmidt and Steve Vinoski have written for the C++ Report magazine detail various threading models useful for distributed object programming, include thread-per-request, thread-pools, thread-per-session, and thread-per-object. You might want to check these columns out at here.
  
  • Single-threaded Orbix
  • Thread-per-request (MT Orbix and HP ORB Plus)
  • Thread-pool (MT Orbix)
  • Thread-per-session/object (MT Orbix)

  Other ORBs also support multi-threading, e.g., HP ORB Plus supports thread-per-request, PowerBroker from Expersoft supports a thread-pool model and ORBeline supports thread-per-session. They don't know what models that NEO supports.

  They'll be covering the concurrency models of these other ORBs in their future columns.

  To be honest, they think you'll be rather disappointed in the performance of MT ORBs at this point. They've been running a lot of benchmarks on our 20 CPU SMP Solaris platform using MT Orbix and aren't getting very good results yet...

  Some overhead is due to the way that MT Orbix implements its threading model, which is very general and powerful, but inefficient due to high-levels of context switching. They are aware of the problem and are working to correct this in subsequent releases.

  Other overhead is inherent in using certain concurrency model (such as thread-per-object) on contemporary multi-processors. If you'd like to see a more general explanation of this (i.e., not specific to CORBA) take a look at here.

Corba and Marshalling

• If you want information on performance of marshalling code, have a look at the Philipp Hoschka work.

Corba and Java

• Java is a object oriented programming language. CORBA is a standard for transparent communication between objects regardless of whether they are local or remote (Location transparency) and allows communication between objects implemented in different languages (Implementation transparency).
  Java objects will also need to communicate with other objects across the network and even to objects implemented in C++ or Smalltalk. Thats where CORBA will play a major role in future.
  A java object instantiated as a part of an applet (in a netscape browser) can communicate with an CORBA object (Implemented in Java or C++ or Smalltalk or C) on a server.
  Business systems are implemented in high performance, scalable, transaction oriented distributed computing technologies such as CORBA/DCE/Encina etc. However internet technologies need a different type of technologies. Thats where Java & HTML are very popular. However when the object inside a Java applet (in a Netscape browser) needs to place a order with the Business system it must be a fficient,bidirectional,secure, and language independant way of communication. Thats where CORBA is useful.

• Has OMG already started to work on a language mapping for Java? Given the popularity of Java it would certainly be a strategic move of OMG to come out with a language mapping as soon as possible. I have not looked at any implementation of Java/CORBA yet, but I would suspect that the language mapping differs considerably among different implementations. I now face the upgrade from Orbix 1.3 to 2.0,i.e, from Iona's C++ mapping to the standard C++ mapping, and this is certainly something I want to avoid with Java.

• Iona has already posted a (suggested) IDL to Java mapping on its web site www.iona.ie. Iona claims "OrbixWeb is a full Java implementation of IONA's market-leading Orbix product."

• Headquarters for the campaign to bring OpenDoc to Java : This page contains a mailto link that readers can use to send email to Sun, CILabs, Netscape and JavaWorld magazine The page is getting about 100 hits per day, and generating about 4 email messages per day. Over 150 messages in support of this integration have been sent from the page to date.
  The Java-OpenDoc mailing list has been dead quiet for some time -- there's not much to talk about since you can't use Java and OpenDoc together yet.
  Although Apple will be announcing Java tools for Mac OpenDoc soon, this is not as useful as having Sun support OpenDoc in Java, which would change the way Java is used and propell OpenDoc towards wide acceptance.

Corba and ATM

• A Douglas C. Schmidt's message:
  We are in the process of measuring the performance of the Expersoft PowerBroker implementation of CORBA over ATM. To accomplish this, we must be able to do the following:
  • (1) Force the server to send/receive data over the ATM interface.

    That is, the server must be able to receive data addressed to its IP address that corresponds to the ATM interface, which is *not* the same as the host name. With Orbix and ORBeline this is possible by tweaking various command-line or environment options. However, with PowerBroker these doesn't seem to be an obvious way to make the server listen to a specific IP address.

  • (2) Be able to set the sender/receiver socket queue sizes to the maximum supported (on Solaris 2.4 this is 64 KB).

    However, we can't find any way to access the underlying socket descriptor in PowerBroker in order to set the socket size to the maximum. We can find a few include files related to sockets that had public member functions such as "getHandle", but we could not figure out how to use these classes with the PowerBroker server implementation.

    We applied a brute force method to set the socket sizes. We defined a method in the interface that acts as a pre-processing routine that is called by the client before we start the measurements. In this method, we iterate through the socket descriptors from 3 to "MAX" and set the socket queue sizes.

  Thus far, the performance we obtained transferring 64 MB of data between two hosts over an ATM network using PowerBroker has been very poor, compared to results we obtained for the other ORB implementations we've been testing. However, I suspect that part of the problem centers on our not having figured out the proper hooks to set the options described above.

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