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diff --git a/ACE/TAO/docs/minimumTAO.html b/ACE/TAO/docs/minimumTAO.html new file mode 100644 index 00000000000..56da5f4fa0a --- /dev/null +++ b/ACE/TAO/docs/minimumTAO.html @@ -0,0 +1,275 @@ +<!-- $Id$ --> + +<html> + <head> + <title>Minimum TAO</title> + <link rev=made href="mailto:tao-users@cs.wustl.edu"> + </head> + +<body text = "#000000" + link="#000fff" + vlink="#ff0f0f" + bgcolor="#ffffff"> + +<hr> +<p> + +<strong>Minimum TAO</strong> +<p> + +In addition to our work on <A HREF="../../docs/ACE-subsets.html">ACE +subsetting</A>, we have also been reducing the footprint of TAO. We +are pursuing two complementary strategies to reduce TAO's footprint: + +<OL> + +<LI> <B><EM>Implicit subsetting</EM></B>, e.g., by reducing + dependencies in the TAO library so that programs need not link + unused TAO components. <P> + +<LI> <B><EM>Explicit subsetting</EM></B>, e.g., by supporting the <a +href="http://www.omg.org/cgi-bin/doc?orbos/98-08-04.pdf"><em>minimumCORBA +</em></a> specification to <a href = +"http://www.cs.wustl.edu/~schmidt/TAO.html">TAO</a>. The <em> +minimumCORBA </em> specification removes the following features from +the <a href +="http://www.omg.org/technology/documents/formal/">CORBA</a> +specification. <P> +<ul> +<li>Dynamic Skeleton Interface<br> +<li>Dynamic Invocation Interface<br> +<li>Dynamic Any<br> +<li>Interceptors<br> +<li>Interface Repository<br> +<li>Advanced POA features<br> +<li>CORBA/COM interworking<br> +</ul> +</OL> + +The implicit subsetting of TAO requires no explicit application +programmer intervention. In contrast, to minimize the footprint of +TAO explicitly, you must +<OL> +<LI> <a +href="../../ACE-INSTALL.html">Configure</a> ACE to support only those +components that are required by TAO and <P> +<LI> <a href = +"../../TAO/TAO-INSTALL.html">Configure</a> TAO to only support the +components specified by the <em>minimumCORBA</em> specification. +</OL> + +The following two tables show the footprint reduction achievable via +explicit subsetting. Note that the IDL Compiler column refers to the +code required to collaborate between the IDL compiler and the ORB, and +not to the code for the IDL compiler itself. + +<p><hr width=50% align=left> <p> + +Note: All measurement are for ACE 5.0 and TAO 1.0 using egcs-2.91.60 +on SunOS5.7<P> + +The <a +href="../../ACE-INSTALL.html#flags">make +flags</a> options used were: <P> + +<code> debug=0 optimize=1 static_libs_only=1 DEFFLAGS=-DACE_USE_RCSID=0 </code> <P> + +These options translate into:<P> +<UL> +<LI> No debugging +<LI> Optimization is set to -O2 +<LI> Static ACE and TAO libraries +<LI> Use of RCS Ids is turned off +</UL> +<p> + +To build a TAO static library, if shared libraries are the default, +use <code>make static_libs_only=1</code> (make sure to do this for +ACE, as well). If you're using recent versions of GNU GCC, you can +use the <A HREF="../../ACE-INSTALL.html#repo">-frepo</A> option, which +typically reduces the footprint by another 25 percent. <P> + +<HR> + +<h3><a name="Status">ACE+TAO Subsetting Work in Progress</a></h3> + +We've been tracking the footprint reduction of ACE+TAO periodically +since April, 2000. All the statistics are available <A +HREF="http://www.dre.vanderbilt.edu/Stats/footprint.shtml">online</A>. As the result of +this prior work, we've identified various areas for improvement that +we're now addressing. For example, the following are the remaining +areas for ACE subsetting: + + <ul> + <li><EM><B>Log_Msg decoupling</EM></B> -- We have a good start on this, but it needs work + to finish. It might be easiest to make an abstract + base class, then have ACE_Log_Msg derive from it. That way + we could remove the exposure of all the #includes in Log_Msg.cpp + to applications that don't need it. Another alternative would + be to disable compilation of Log_Msg.cpp when ACE_NLOGGING is + enabled.<p> + + <li><EM><B>Higher layer interdependencies</EM></B> -- We haven't + exhaustively tested all possible combinations of subsets. It's possible + that there are interdependencies between some layers that + we haven't yet identified and removed.<p> + + <li><EM><B>Remove reliance on multiple inheritance</EM></B> -- Multiple + inheriance is only used in a few + places in ACE. This + isn't really a subsetting problem, but is necessary to + fully take advantage of optimizations available on C++ compilers for + embedded systems.<p> + </ul> + +We anticipate that these changes should reduce the default size of ACE +by around 100-200 kbytes.<P> + +As the effort to reduce TAO's footprint continues, we are planning +several modifications for TAO that should reduce the footprint for +both the full CORBA and minimum CORBA configurations by around 300-400 +Kbytes. The list below contains an estimate of the impact of each one +of these changes, along with the estimated effort to implement them. +</P> + +<P> + <TABLE CELLPADDING=4 BORDER=4> + <TR> + <TD>Component</TD><TD>Impact</TD><TD>Effort</TD> + <TD>Description</TD> + </TR> + <TR> + <TD>ACE</TD><TD>14 Kb</TD><TD>4 weeks</TD> + <TD> + Implement a TAO-specific Reactor. + ACE's reactor supports a number of features that TAO does not + require. Thus, a TAO-specific implementation is an important way to + reduce the footprint. + </TD> + </TR> + <TR> + <TD>ACE</TD><TD>20 Kb</TD><TD>4 weeks</TD> + <TD> + Implement a TAO-specific Service Configurator. + TAO uses the ACE Service Configurator to dynamically configure + its strategies. In many embedded applications the set of + strategies are selected at design-time, on those platforms it + would be appropriate to disable all the features to + dynamically load components into the ORB. + </TD> + </TR> + <TR> + <TD>TAO</TD><TD>10-15 Kb</TD><TD>1-2 weeks</TD> + <TD> + Eliminate duplicate code due to instantiations of string -> + pointer maps. TAO uses several such maps, they could be replaced by a + generic version, wrapped with a fully inlined (i.e. zero + footprint) adapter for type-safety. + </TD> + </TR> + <TR> + <TD>TAO</TD><TD>3-10 Kb</TD><TD>1-2 weeks</TD> + <TD> + Make message buffering strategies optional. + TAO supports policy extensions to control the outgoing oneway and AMI + request buffers. Those policies are not used by all + applications. + </TD> + </TR> + <TR> + <TD>TAO</TD><TD>10 Kb</TD><TD>2 weeks</TD> + <TD> + Make support for multiple ORBs optional. + TAO can support multiple ORBs in the same process, but most + applications only require one. + </TD> + </TR> + <TR> + <TD>TAO</TD><TD>5 Kb</TD><TD>1 week</TD> + <TD> + Move the less common transport muxing and reply waiting + strategies to an optional library. + </TD> + </TR> + <TR> + <TD>ACE+TAO</TD><TD>30 Kb</TD><TD>8 weeks</TD> + <TD> + Decouple ACE (and then TAO) from the + <CODE>ACE_Thread_Manager</CODE> component. + This component is only used in the thread-per-connection + model, if we could decouple it in ACE then TAO could be + modified to only link this component when that concurrency + model is enabled. + </TD> + </TR> + <TR> + <TD>TAO</TD><TD>>50 Kb</TD><TD>6 weeks</TD> + <TD> + Move <CODE><<=</CODE> and <CODE>>>=</CODE> + operators to separate files. + Currently TAO includes nearly 500 such operators, moving them + to separate files (grouped by component?) would eliminate them + from most applications. + </TD> + </TR> + </TABLE> +</P> + +<P>In parallel with the activities described above we are pursuing +other avenues of research to find sources of rarely used or unused +code in ACE+TAO, and to modify the software to eliminate such code. +These activities include the following:</P> + +<UL> + <LI><P> + Using profiling tools, such as gprof, Quantify and True Coverage + to find unreachable code, or code only reachable in certain + applications. + </P></LI> + <LI><P> + The code TAO's IDL compiler generates for <CODE>CORBA::Any</CODE> + operators is large, so we are evaluating designs that reduce the impact of the <CODE>CORBA::Any</CODE> + type support. TAO's IDL compiler already makes that support optional. + However, for applications that require <CODE>Anys</CODE> it may be useful to separate that code + in another file to reduce the size of generated stubs and skeletons, + without losing the opportunity to use more dynamic CORBA invocation + modes. + </P></LI> + <LI><P> + The Notification Service currently depends on the Trading service to + implement the Trader Constraint Language. We are planning to break that + dependency and factor the TCL parser into a smaller library shared + by both services. + </P></LI> + <LI><P> + TAO still contains features that are rarely or never used. + Examples include the interfaces to query the well-known services and + to dynamically discover the level of security support. Those + components should only be linked (dynamically) in applications that require them. + </P></LI> + <LI><P> + The support for interceptors currently generated by the IDL compiler + can be partially refactored into common ORB code. + Moreover, we evaluating a new implementation of interceptors + that can be configured dynamically, thereby eliminating the need for + compile-time configuration flags. + </P></LI> + <LI><P> + We are planning to provide compile-time flags to eliminate certain mandatory features + in CORBA that are not used in all applications, such as IOR + parsers (corbaloc, corbaname, etc.). + </P></LI> + <LI><P> + Finally, we will perfom more code inspections to determine if template code can be + refactored into base classes and thereby shared by many objects in + the ACE+TAO implementations. + </P></LI> +</UL> + +Although we do not yet have sufficient insights to know how much +footprint reduction these activities will afford, we anticipate these +enhancements could reduce the default footprint of TAO by another +100-200 Kbytes. + +</body> +</html> |