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<H1 CLASS="chapter"><A NAME="htoc1">Chapter 1</A>  Introduction</H1><P>omniORBpy is an Object Request Broker (ORB) that implements the CORBA
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2.6 Python mapping [<A HREF="omniORBpy011.html#pythonmapping">OMG01b</A>]. It works in conjunction with
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omniORB for C++, version 4.1.</P><P>This user guide tells you how to use omniORBpy to develop CORBA
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applications using Python. It assumes a basic understanding of CORBA,
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and of the Python mapping. Unlike most CORBA standards, the Python
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mapping document is small, and quite easy to follow.</P><P>This manual contains all you need to know about omniORB in order to
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use omniORBpy. Some sections are repeated from the omniORB manual.</P><P>In this chapter, we give an overview of the main features of omniORBpy
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and what you need to do to setup your environment to run it.</P><H2 CLASS="section"><A NAME="toc1"></A><A NAME="htoc2">1.1</A>  Features</H2><H3 CLASS="subsection"><A NAME="htoc3">1.1.1</A>  Multithreading</H3><P>omniORB is fully multithreaded. To achieve low call overhead,
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unnecessary call-multiplexing is eliminated. With the default
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policies, there is at most one call in-flight in each communication
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channel between two address spaces at any one time. To do this without
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limiting the level of concurrency, new channels connecting the two
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address spaces are created on demand and cached when there are
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concurrent calls in progress. Each channel is served by a dedicated
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thread. This arrangement provides maximal concurrency and eliminates
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any thread switching in either of the address spaces to process a
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call. Furthermore, to maximise the throughput in processing large call
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arguments, large data elements are sent as soon as they are processed
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while the other arguments are being marshalled. With GIOP 1.2, large
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messages are fragmented, so the marshaller can start transmission
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before it knows how large the entire message will be.</P><P>From version 4.0 onwards, omniORB also supports a flexible thread
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pooling policy, and supports sending multiple interleaved calls on a
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single connection. This policy leads to a small amount of additional
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call overhead, compared to the default thread per connection model,
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but allows omniORB to scale to extremely large numbers of concurrent
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clients.</P><H3 CLASS="subsection"><A NAME="htoc4">1.1.2</A>  Portability</H3><P>omniORB has always been designed to be portable. It runs on many
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flavours of Unix, Windows, several embedded operating systems, and
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relatively obscure systems such as OpenVMS and Fujitsu-Siemens BS2000.
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It is designed to be easy to port to new platforms. The IDL to C++
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mapping for all target platforms is the same.</P><H3 CLASS="subsection"><A NAME="htoc5">1.1.3</A>  Missing features</H3><P>
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<A NAME="sec:missing"></A></P><P>omniORB is not (yet) a complete implementation of the CORBA 2.6 core.
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The following is a list of the most significant missing features.</P><UL CLASS="itemize"><LI CLASS="li-itemize">omniORB does not have its own Interface Repository. However, it
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can act as a client to an IfR. The omniifr project
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(<A HREF="http://omniifr.sourceforge.net/"><TT>http://omniifr.sourceforge.net/</TT></A>) aims to create an IfR for
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omniORB.</LI><LI CLASS="li-itemize">omniORB supports interceptors, but not the standard Portable
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Interceptor API. Interceptor facilities available from Python code are
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quite limited.</LI></UL><P>These features may be implemented in the short to medium term. It is
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best to check out the latest status on the omniORB home page
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(<A HREF="http://omniorb.sourceforge.net/"><TT>http://omniorb.sourceforge.net/</TT></A>).</P><H2 CLASS="section"><A NAME="toc2"></A><A NAME="htoc6">1.2</A>  Setting up your environment</H2><P>
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<A NAME="sec:setup"></A></P><P>omniORBpy relies on the omniORB C++ libraries. If you are building
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from source, you must first build omniORB itself, as detailed in the
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omniORB documentation. After that, you can build the omniORBpy
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distribution, according to the instructions in the release notes.</P><H3 CLASS="subsection"><A NAME="htoc7">1.2.1</A>  Paths</H3><P>With an Autoconf build (the norm on Unix platforms), omniORBpy is
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usually installed into a location that Python will find it.</P><P>Otherwise, you must tell Python where to find it. You must add two
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directories to the <TT>PYTHONPATH</TT> environment variable. The
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<TT>lib/python</TT> directory contains platform-independent Python code;
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the <TT>lib/</TT><TT>$</TT><TT>FARCH</TT> directory contains
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platform-specific binaries, where <TT>FARCH</TT> is the name of
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your platform, such as <TT>x86_win32</TT>.</P><P>On Unix platforms, set <TT>PYTHONPATH</TT> with a command like:</P><PRE CLASS="verbatim"> export PYTHONPATH=$PYTHONPATH:$TOP/lib/python:$TOP/lib/$FARCH
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</PRE><P>On Windows, use</P><PRE CLASS="verbatim"> set PYTHONPATH=%PYTHONPATH%;%TOP%\lib\python;%TOP%\lib\x86_win32
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</PRE><P>(Where the <TT>TOP</TT> environment variable is the root of your
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omniORB tree.)</P><P>You should also add the <TT>bin/</TT><TT>$</TT><TT>FARCH</TT> directory
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to your <TT>PATH</TT>, so you can run the IDL compiler, omniidl.
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Finally, add the <TT>lib/</TT><TT>$</TT><TT>FARCH</TT> directory to
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<TT>LD_LIBRARY_PATH</TT>, so the omniORB core library can be found.</P><H3 CLASS="subsection"><A NAME="htoc8">1.2.2</A>  Configuration file</H3><UL CLASS="itemize"><LI CLASS="li-itemize">On Unix platforms, the omniORB runtime looks for the environment
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variable <TT>OMNIORB_CONFIG</TT>. If this variable is defined, it
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contains the pathname of the omniORB configuration file. If the
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variable is not set, omniORB will use the compiled-in pathname to
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locate the file (by default <TT>/etc/omniORB.cfg</TT>).</LI><LI CLASS="li-itemize">On Win32 platforms (Windows NT, 2000, 95, 98), omniORB first
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checks the environment variable <TT>OMNIORB_CONFIG</TT> to obtain the
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pathname of the configuration file. If this is not set, it then
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attempts to obtain configuration data in the system registry. It
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searches for the data under the key
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<TT>HKEY_LOCAL_MACHINE\SOFTWARE\omniORB</TT>.</LI></UL><P>omniORB has a large number of parameters than can be configured. See
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chapter <A HREF="omniORBpy004.html#chap:config">4</A> for full details. The files
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<TT>sample.cfg</TT> and <TT>sample.reg</TT> contain an example
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configuration file and set of registry entries respectively.</P><P>To get all the omniORB examples running, the main thing you need to
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configure is the Naming service, omniNames. To do that, the
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configuration file or registry should contain an entry of the form</P><PRE CLASS="verbatim"> InitRef = NameService=corbaname::my.host.name
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</PRE><P>See section <A HREF="omniORBpy006.html#sec:corbaname">6.1.2</A> for full details of corbaname URIs.</P><HR>
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