Current Status of TAO

In addition, we've gotten TAO to interwork with many other ORBs (e.g., Orbix, JacORB, ORB Express, VisiBroker, etc.), so we're confident that its IIOP implementation is robust and interoperable. See the TAO Press Release and TAO Success Stories pages for information on TAO's use in commercial projects.

TAO contains the components shown in Figure 1.

Figure 1. The TAO ORB Endsystem Architecture

Each of these TAO components is outlined below:

• IDL Compiler -- TAO's IDL compiler is based on the enhanced version of the freely available SunSoft IDL compiler. The latest CORBA 3.x IDL-to-C++ mapping has been implemented, including the latest POA features. The IDL compiler also supports the Object-by-Value specification and the CORBA Messaging specification. Moreover, TAO's IDL compiler can generate code for client and server asynchronous invocations.

  TAO's IDL compiler generates compiled stubs/skeletons which are quite efficient. In addition, TAO's IDL compiler can generate stubs/skeletons that can support either native C++ exceptions or the more portable CORBA::Environment approach. TAO's IDL compiler also generates code for smart proxies that allow 3rd party applications to ``plug'' features into clients and portable interceptors that implement the Interceptor pattern.

• Inter-ORB Protocol Engine -- TAO contains a highly optimized protocol engine that implements the CORBA 3.x General/Internet Inter-ORB Protocol (GIOP/IIOP), version 1.0, 1.1, and 1.2. TAO can therefore interoperate seamlessly with other ORBs that use the standard IIOP protocol. TAO's protocol engine supports both the static and dynamic CORBA programming models, i.e., SII/SSI and DII/DSI, respectively. TAO also supports Dynamic Anys, which facilitate incremental demarshaling.

  In addition, TAO supports a pluggable protocols framework that enables GIOP messages to be exchanged over non-TCP transports, including shared memory, UDP unicast, UDP multicast, UNIX-domain sockets, Secure Sockets (SSL), and VME backplanes. TAO's pluggable protocols framework is important for DRE applications that require more stringent QoS protocol properties than TCP/IP provides.

• ORB Core -- TAO's ORB Core provides an efficient, scalable, and predictable two-way, one-way, and reliable one-way synchronous and asynchronous communication infrastructure for high-performance and real-time applications. It provides the following concurrency models: (1) reactive, (2) thread-per-connection, (3) thread pool (including the Real-time CORBA thread pool API), and (4) reactor-per-thread-priority (which is optimized for deterministic real-time systems). TAO's ORB Core supports nested upcalls with all its concurrency models.

  TAO's ORB Core is based on patterns and frameworks in ACE. The key patterns and ACE frameworks used in TAO include the Acceptor and Connector, Reactor, Active Object, Half-Sync/Half-Async, and Service Configurator.

• Portable Object Adapter -- TAO's implementation of the CORBA Portable Object Adapter (POA) is designed using patterns that provide an extensible and highly optimized set of request demultiplexing strategies, such as perfect hashing and active demultiplexing, for objects identified with either persistent or transient object references. These strategies allow TAO's POA to provide constant-time lookup of servants based on object keys and operation names contained in CORBA requests.

• An Implementation Repository that automatically launches servers in response to client requests.

• An Interface Repository that provides run-time information about IDL interfaces.

1. Audio/Video Streaming Service -- TAO's A/V Streaming Service implements the standard Control and Management of Audio/Video Streams Specification. The service has been integrated and tested with the QuO framework. The integration demonstrated the applicability of standard middleware for applications that can adapt to changes in resource availability and QoS requirements.

2. Concurrency Service -- TAO's Concurrency Service provides a mechanism that allows clients to acquire and release various types of locks in a distributed system. Note that TAO only currently supports a subset of the Concurrency Service, i.e., the non-transactional part.

3. Event Service -- TAO's Event Service supports decoupled communication among multiple suppliers and consumers using the standard GIOP/IIOP protocol.

4. Lifecycle Service -- TAO's Lifecycle Service provides a standard means to locate, move, copy, and remove objects.

5. Logging Service -- TAO's implementation of the OMG's Telecom Log Service allows applications to send logging records to a centralized logging server.

6. Naming Service -- TAO's Naming Service supports both persistent and non-persistent hierarchical mappings between sequences of strings and object references. In addition, TAO supports the Interoperable Naming Service, which defines a standard way for clients and servers to locate the Naming Service, as well as any other CORBA service.

7. Notification Service -- TAO's Notification Service is a more powerful form of the Event Service that supports filtering and correlation.

8. Persistent State Service -- TAO's Persistent State Service (PSS) provides a way to make a service persistent. PSS presents persistent information as storage objects that reside in storage homes.

9. Property Service -- TAO's Property Service allows applications to associate properties with objects dynamically. The Property Service is used by TAO's A/V Streaming Service to transmit QoS information.

10. Security Service -- TAO provides an implementation of portions of the CORBA Security Service.

11. Time Service -- TAO's Time Service provides globally synchronized time to distributed clients.

12. Trading Service -- TAO's Trading Service implements a mapping between attribute constraints and sequences of object references that match those constraints.

1. Load Balancing Service -- TAO's Load Balancing Service implements round robin and minimum dispersion algorithms to help balance out the load across a group of machines.

2. Real-time Event Service -- TAO's Real-time Event Service augments the standard CORBA Event Service model by providing source and type-based filtering, event correlations, real-time dispatching, and UDP/IP multicast communication.

3. Scheduling Service -- TAO's real-time Scheduling Service supports static rate monotonic scheduling and dynamic maximum urgency first scheduling to assign priorities and validate schedulability. It is currently integrated with TAO's Real-time Event Service, though we're ultimately planning to integrate this with the ORB. In addition, we are enhancing our Scheduling Service to conform to the Scheduling Service defined in the new Real-time CORBA specification, as well as the forthcoming dynamic scheduling specification.

Work in Progress

• An open-source implementation of the CORBA Object Transaction Service (OTS).

• New optimizations for TAO's IIOP protocol engine, ORB Core, and Object Adapter to improve its performance, predictibility, and memory footprint for high-performance and real-time systems.

• Adding the latest CORBA Security Service features to TAO.

Fundable Work

• The entire CORBA Messaging specification, which provides an asynchronous method invocation (AMI) mechanism and a standard API for specifying QoS parameters. We have enhanced TAO's IDL compiler and run-time system to support the standard AMI callback model. Support for the AMI polling model and the time-independent invocations (TII) would desirable.

• Additional ORB concurrency models, e.g., asynchronous thread pool using the Proactor, thread-per-request and thread-per-object.

• We are interested in having someone sponsor TAO being branded as a CORBA-compliant ORB by The Open Group when their test-suite matures to cover later versions of CORBA.

• Additional protocols for TAO's Pluggable Protocols framework, including sockets, TP4, SS7, ATM, GSMP, and Fibrechannel. It would also be nice to have funding to complete the OMG's Extensible Transport Framework.

• The forthcoming CORBA Wireless Access and Control specification, which will provide CORBA service in the presence of personal and terminal mobility.

Getting Involved

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