Program for Thursday, 14 March 2002

Our Next Meeting is scheduled for
Thursday, 14 March 2002
Currie Colket will be speaking on
Ada 95 Protected Objects for Synchronizing Shared Data Structures
at the New MITRE Building in McLean, Virginia

Please note that this is a new meeting location for our March Meeting

This will be a joint meeting between the DC and Baltimore SIGAda Chapters


To Members and Friends of DC SIGAda

Next Meeting:

Thursday, 14 March 2002, 7:30 P.M. (Refreshments and Social at 7:00 P.M.) at the new MITRE2 Building in McLean, Virginia. DC SIGAda and Baltimore SIGAda will feature a presentation titled: Ada 95 Protected Objects for Synchronizing Shared Data Structures


Ada 95 Protected Objects for Synchronizing Shared Data Structures

Software systems frequently have the need to share critical data where two or more tasks must synchronize their manipulations of shared data structures. The need is readily apparent when one considers one task updating the latitude and longitude of a track while other tasks access this latitude and longitude. If the task updating the coordinates gets suspended after the latitude is updated and before the longitude gets updated, it is possible for a second task to access the updated latitude and an older longitude. This is clearly not useful for an application attempting to accurately target the track. There are requirements to effectively synchronize data in many domains ranging from avionics to financial. There are many applications where this inconsistent data would violate data integrity and safety constraints.

In Ada 83, the rendezvous was used for both inter-task communication and for synchronizing access to shared data structures. This was safe, but the rendezvous resulted in a relatively high overhead to share data structures safely. One of the nice new features of Ada 95 was the addition of Protected Objects. A Protected Object provides a safe data-oriented synchronization mechanism that is highly efficient.

This presentation will start at the basics discussing protected types, protected objects, and protected operations. It will discuss the Ada Language Reference Manual syntax with a number of useful examples. Quality and Style is also important. Recommended styles and usage from the Ada Quality and Style Guide will be addressed. Issues resulting from actual use on real systems will be presented. It is possible to obtain information on the use of protected objects from analysis tools. Thoughts on this type of analysis will be included and opportunities to brainstorm alternative uses will be presented.


Mr. Currie Colket is the Chair of ACM SIGAda, the Chair of the SIGAda Ada Semantic Working Group, and Chair of the ISO WG9 ASIS Rapporteur Group. He recently retired from the DoD where he served in the Air Force as an Airborne Surveillance Officer on AWACS and a computer scientist for the United States Navy. Mr. Colket is currently a software systems engineer for MITRE. His current tasks involve software engineering support for a variety of programs. Prior to his affiliation with MITRE, he was a consultant for the Software Program Manager's Network (SPMN). He has a Bachelor of Science from Case Institute of Technology, a Master of Business Administration from the University of Southern Mississippi and a Master of Science in Computer Science from the Ohio State University. His coordinates are:

Currie Colket
The MITRE Corporation
7515 Colshire Drive
McLean, Virginia 22102-7508

Phone: +1 (703) 883-7381
FAX: +1 (703) 883-1339
Email: colket@mitre.org


Room 1N100 A/B
The MITRE Corporation
7515 Colshire Drive
McLean, Virginia 22102-7508


MITRE2 is on Colshire Drive just inside the beltway south of Route 123.

Those coming from the Dulles Access Toll Road or I-495 north of the Dulles Access Toll Road will want to access Colshire Drive by:

1. Take the Dulles Airport Access and Toll Road to Exit 19;
   (From I-495, this is labeled "To East I-66");
2. Take Exit 19A;
   (following signs to Route 123 South, Tysons Corner);
3. Bear right onto Route 123 (towards Tysons Corner)
4. Turn left onto Colshire Drive (at first light);

Those coming from I-495 south of Route 123 (Dolley Madison Boulevard) will want to access Colshire Drive by:

1. Take Exit 46B (McLean, Route 123);
2. Go North onto Route 123;
3. Turn right onto Colshire Drive (at second light);

From Colshire Road and Route 123:

A. Take third right OFF OF THE TRAFFIC CIRCLE;
   (a logical left hand turn);
B. Proceed ~ 50 meters; Turn right into parking garage.
C. Visitor Parking is located on Levels 2 and 3
   (the walkway to the lobby is on Parking Level 2)
D. If door is locked, contact Security using phone by door
   (at entrance to MITRE2 from the Parking Garage)
E. Check in with Security at Security desk in lobby
   (You will need a photo ID)

To obtain a map of MITRE2 Building and the MITRE Campus, visit =>

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We will have light foods and refreshment at 7:00. The meeting begins at 7:30 pm.

Many thanks to all earlier participants, contributors, speakers, advisors, and friends, who are involved in helping to produce and attend the meetings.

Please forward this message to people who might be interested in attending. We welcome all new members as our attendance and interests grow.

Consider registering for inclusion on our e-mail list. Registration instructions are provided on the DC SIGAda Web site.

Jeff Castellow, Chair, DC SIGAda

updated 6 March 2002