In addition to our work on ACE subsetting, we have also been reducing the footprint of TAO. We are pursuing two complementary strategies to reduce TAO's footprint:
Note: All measurement are for ACE 5.0 and TAO 1.0 using egcs-2.91.60 on SunOS5.7
The make flags options used were:
debug=0 optimize=1 static_libs_only=1 DEFFLAGS=-DACE_USE_RCSID=0
These options translate into:
To build a TAO static library, if shared libraries are the default,
make static_libs_only=1 (make sure to do this for
ACE, as well). If you're using recent versions of GNU GCC, you can
use the -frepo option, which
typically reduces the footprint by another 25 percent.
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.
|ACE||14 Kb||4 weeks||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.|
|ACE||20 Kb||4 weeks||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.|
|TAO||10-15 Kb||1-2 weeks||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.|
|TAO||3-10 Kb||1-2 weeks||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.|
|TAO||10 Kb||2 weeks||Make support for multiple ORBs optional. TAO can support multiple ORBs in the same process, but most applications only require one.|
|TAO||5 Kb||1 week||Move the less common transport muxing and reply waiting strategies to an optional library.|
|ACE+TAO||30 Kb||8 weeks||
Decouple ACE (and then TAO) from the
|TAO||>50 Kb||6 weeks||
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:
Using profiling tools, such as gprof, Quantify and True Coverage to find unreachable code, or code only reachable in certain applications.
The code TAO's IDL compiler generates for
operators is large, so we are evaluating designs that reduce the impact of the
type support. TAO's IDL compiler already makes that support optional.
However, for applications that require
Anys 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
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.
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.
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.
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.).
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.