| -- 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 ; |