The Ada programming language is unique in its high-level concurrency facilities, supported by a secure and powerful set of programming constructs. Ada 95 now has additional capabilities, specifically the protected type construct.Although the Ada rendezvous is prone to deadlock, a careful discipline can ensure that this type of dead state does not occur. Restricting task communication assists in preventing deadlock, yet such restrictions may be too limiting and/or too inefficient for an application. Indeed, several researchers have suggested that deadlock should not be prevented, but monitored and corrected during testing and/or run time.This paper takes the position that deadlock should be prevented by following specific guidelines in the use of the rendezvous. We define deadlock, show how it can occur with Ada tasks, and outline mechanisms that are appropriate for its control.
There has been a continued interest in software reuse in the software engineering community, as evidenced by web services and Microsoft .NET, and by the continued work in product-line engineering. New users to software reuse should be made aware of the work that has been done by the Ada community and of the particular appropriateness of Ada for reuse. We therefore review in this column the issues involved in reuse with the Ada programming language. For those who are interested in investigating these topics in depth, we enclose a brief list of helpful sources. We will post this column on our web site, and gladly append any additional references that our readers may supply.
This column consists of our January 2010 listing of sources for reusable software components. All information is obtained from web sites or directly from the parties involved. As always, no recommendation or guarantee by this column is implied. We note that this issue marks twenty years of this column appearing in Ada Letters.
This c o l u m n c o n s i s t s of our y e a r l y listing of reuse s o u r c e s . A s a l w a y s , no r e c o m m e n d a t i o n or g u a r a n t e e by t h i s c o l u m n is implied. REUSE P R O D U C T S ACES(TOOL, UNRESTRICTED)The A d a C o m p i l e r Evaluation S y s t e m (ACES) Ver.sion 2.1 is a c o l l e c t i o n of p e r f o r m a n c e tests, t e s t m a n a g e m e n t tools, a n a l y s i s t o o l s , and a s s e s s m e n t p r o c e d u r e s t h a t p e r m i t u s e r s to collect and analyze data on p e r f o r m a n c e and u s a b i l i t y c h a r a c t e r i s t i c s of A d a i m p l e m e n t a t i o n s . Funded by t h e A J P O , the ACES is a m e r g e r of the A d a C o m p i l e r E v a l u a t i o n C a p a b i l i t y (ACEC) and t h e A d a E v a l u a t i o n S y s t e m (AES). V e r s i o n 2.1 of t h e ACES i n c l u d e s o v e r 1 0 0 t e s t s for l a n g u a g e f e a t u r e s i n t r o d u c e d b y A d a 95". O t h e r i m p r o v e m e A d a in A c t i o n (UTILITIES, UNRESTRICTED) A d a in A c t i o n ( w i t h Practical P r o g r a m m i n g Examples) by D o -W h i l e J o n e s is n o w on t h e Internet. T h a n k s to t h e w o r k of Chris M o r g a n , and the g e n e r o s i t y of Dirk C r a e y n e s t and A d a -B e l g i u m , A d a in A c t i o n is n o w on t h e w e b at
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