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-- C97201X.ADA

--                             Grant of Unlimited Rights

--

--     Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687,

--     F08630-91-C-0015, and DCA100-97-D-0025, the U.S. Government obtained 

--     unlimited rights in the software and documentation contained herein.

--     Unlimited rights are defined in DFAR 252.227-7013(a)(19).  By making 

--     this public release, the Government intends to confer upon all 

--     recipients unlimited rights  equal to those held by the Government.  

--     These rights include rights to use, duplicate, release or disclose the 

--     released technical data and computer software in whole or in part, in 

--     any manner and for any purpose whatsoever, and to have or permit others 

--     to do so.

--

--                                    DISCLAIMER

--

--     ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR

--     DISCLOSED ARE AS IS.  THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED 

--     WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE

--     SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE 

--     OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A

--     PARTICULAR PURPOSE OF SAID MATERIAL.

--*

-- CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF BOTH PARTNERS REFUSE TO

--     WAIT (THAT IS, IF THE ENTRY CALL IS ISSUED BY A

--     "CONDITIONAL_ENTRY_CALL" AND THUS FOLLOWS A NO-WAIT POLICY

--     (DEMANDING UNCONDITIONALLY THAT "YOU DO IT   N O W  , OR ELSE"),

--     WHILE THE CALLEE IS ALSO COMMITTED TO A NO-WAIT POLICY,

--     BY VIRTUE OF A SELECTIVE_WAIT STATEMENT OF THE THIRD KIND

--     (WITH AN "ELSE" PART) IN WHICH THE CORRESPONDING ACCEPT_STATEMENT

--     IS EMBEDDED).

--     ("CLOSE ENCOUNTERS OF THE THIRD KIND"  --  ARE THEY POSSIBLE?)

-- THE SEMANTICS OF THIS ENTRY CALL REQUIRES THAT THE CALLING TASK

--     N O T   ENTER ITSELF ON ANY QUEUE BUT RATHER ATTEMPT AN IMMEDIATE

--     RENDEZVOUS WHICH IS TO TAKE PLACE IF AND ONLY IF THE CALLED TASK

--     HAS REACHED A POINT WHERE IT IS READY TO ACCEPT THE CALL (I.E.

--     IT IS EITHER WAITING AT AN ACCEPT STATEMENT FOR THE CORRESPONDING

--     ENTRY OR IT IS WAITING AT A SELECTIVE_WAIT STATEMENT WITH AN OPEN

--     ALTERNATIVE STARTING WITH SUCH AN ACCEPT STATEMENT).  IT ALSO

--     REQUIRES THAT THE ENTRY CALL BE CANCELLED IF THE CALLED TASK 

--     IS NOT AT SUCH A POINT.  ON THE OTHER HAND, THE SEMANTICS OF THE

--     SELECTIVE_WAIT STATEMENT WITH AN  'ELSE'  PART  SPECIFIES THAT

--     THE  'ELSE'  PART  MUST BE SELECTED IF NO 'ACCEPT' ALTERNATIVE

--     CAN BE IMMEDIATELY SELECTED,  AND THAT SUCH AN ALTERNATIVE

--     IS DEEMED TO BE IMMEDIATELY SELECTABLE ("SELECTION OF ONE SUCH

--     ALTERNATIVE OCCURS IMMEDIATELY"), AND A CORRESPONDING RENDEZVOUS

--     POSSIBLE,  IF AND ONLY IF THERE IS A CORRESPONDING ENTRY CALL

--     W A I T I N G   TO BE ACCCEPTED.  A "CONDITIONAL ENTRY CALL"

--     NEVER WAITS, AND IS NEVER ENTERED IN WAIT QUEUES; IT TAKES

--     THE 'ELSE' PART INSTEAD.

-- NOTE: IF THIS TEST PROGRAM HANGS UP, THE COMPILER WILL BE DEEMED

--     TO HAVE FAILED.

-- RM 3/19/82

WITH REPORT; USE REPORT;

PROCEDURE C97201X IS

     RENDEZVOUS_OCCURRED        :  BOOLEAN  :=  FALSE ;

     CALLER_TAKES_WRONG_BRANCH  :  BOOLEAN  :=  TRUE  ;

     SERVER_TAKES_WRONG_BRANCH  :  BOOLEAN  :=  TRUE  ;

     QUEUE_NOT_EMPTY            :  BOOLEAN  :=  FALSE ;

BEGIN

     TEST ("C97201X", "CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF" &

                      " BOTH PARTNERS REFUSE TO WAIT" );

     DECLARE

          TASK  T  IS

               ENTRY  SYNCHRONIZE ;

               ENTRY  DO_IT_NOW_ORELSE( DID_YOU_DO_IT : IN OUT BOOLEAN);

               ENTRY  KEEP_ALIVE  ;

          END  T ;

          TASK BODY  T  IS

          BEGIN

               ACCEPT  SYNCHRONIZE ;

               IF  DO_IT_NOW_ORELSE'COUNT /= 0  THEN

                    QUEUE_NOT_EMPTY := TRUE ;

               END IF;

               SELECT

                         ACCEPT  DO_IT_NOW_ORELSE

                                      ( DID_YOU_DO_IT : IN OUT BOOLEAN )

                         DO

                              DID_YOU_DO_IT  :=  TRUE ;

                         END ;

               ELSE         -- (I.E. TASK ADOPTS NO-WAIT POLICY)

                            -- 'ELSE' BRANCH MUST THEREFORE BE CHOSEN

                    SERVER_TAKES_WRONG_BRANCH := FALSE ;

               END SELECT;

               IF  DO_IT_NOW_ORELSE'COUNT /= 0  THEN

                    QUEUE_NOT_EMPTY := TRUE ;

               END IF;

               ACCEPT  KEEP_ALIVE ;  -- TO PREVENT THIS SERVER TASK FROM

                                     --     TERMINATING IF IT GETS TO

                                     --     THE NO-WAIT MEETING-PLACE

                                     --     AHEAD OF THE CALLER (WHICH

                                     --     WOULD LEAD TO A SUBSEQUENT

                                     --     TASKING_ERROR AT THE TIME OF

                                     --     THE NO-WAIT CALL).

          END  T ;

     BEGIN

          T.SYNCHRONIZE ;  -- TO MINIMIZE THE   N E E D   TO WAIT

          SELECT

               T.DO_IT_NOW_ORELSE ( RENDEZVOUS_OCCURRED );

          ELSE              -- (I.E. CALLER TOO ADOPTS A NO-WAIT POLICY)

                                    -- MUST THEREFORE CHOOSE THIS BRANCH

               CALLER_TAKES_WRONG_BRANCH := FALSE ;

          END SELECT;

          T.KEEP_ALIVE ;    -- THIS ALSO UPDATES THE NONLOCALS

     END;   -- END OF BLOCK CONTAINING THE NO-WAIT ENTRY CALL

     IF  RENDEZVOUS_OCCURRED

     THEN

          FAILED( "RENDEZVOUS OCCURRED" );

     END IF;

     IF  CALLER_TAKES_WRONG_BRANCH  OR

         SERVER_TAKES_WRONG_BRANCH

     THEN

          FAILED( "WRONG BRANCH TAKEN" );

     END IF;

     IF  QUEUE_NOT_EMPTY

     THEN

          FAILED( "ENTRY QUEUE NOT EMPTY" );

     END IF;

     RESULT;

END  C97201X ;