1-- C97201X.ADA 2 3-- Grant of Unlimited Rights 4-- 5-- Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687, 6-- F08630-91-C-0015, and DCA100-97-D-0025, the U.S. Government obtained 7-- unlimited rights in the software and documentation contained herein. 8-- Unlimited rights are defined in DFAR 252.227-7013(a)(19). By making 9-- this public release, the Government intends to confer upon all 10-- recipients unlimited rights equal to those held by the Government. 11-- These rights include rights to use, duplicate, release or disclose the 12-- released technical data and computer software in whole or in part, in 13-- any manner and for any purpose whatsoever, and to have or permit others 14-- to do so. 15-- 16-- DISCLAIMER 17-- 18-- ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR 19-- DISCLOSED ARE AS IS. THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED 20-- WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE 21-- SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE 22-- OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A 23-- PARTICULAR PURPOSE OF SAID MATERIAL. 24--* 25-- CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF BOTH PARTNERS REFUSE TO 26-- WAIT (THAT IS, IF THE ENTRY CALL IS ISSUED BY A 27-- "CONDITIONAL_ENTRY_CALL" AND THUS FOLLOWS A NO-WAIT POLICY 28-- (DEMANDING UNCONDITIONALLY THAT "YOU DO IT N O W , OR ELSE"), 29-- WHILE THE CALLEE IS ALSO COMMITTED TO A NO-WAIT POLICY, 30-- BY VIRTUE OF A SELECTIVE_WAIT STATEMENT OF THE THIRD KIND 31-- (WITH AN "ELSE" PART) IN WHICH THE CORRESPONDING ACCEPT_STATEMENT 32-- IS EMBEDDED). 33-- ("CLOSE ENCOUNTERS OF THE THIRD KIND" -- ARE THEY POSSIBLE?) 34 35 36-- THE SEMANTICS OF THIS ENTRY CALL REQUIRES THAT THE CALLING TASK 37-- N O T ENTER ITSELF ON ANY QUEUE BUT RATHER ATTEMPT AN IMMEDIATE 38-- RENDEZVOUS WHICH IS TO TAKE PLACE IF AND ONLY IF THE CALLED TASK 39-- HAS REACHED A POINT WHERE IT IS READY TO ACCEPT THE CALL (I.E. 40-- IT IS EITHER WAITING AT AN ACCEPT STATEMENT FOR THE CORRESPONDING 41-- ENTRY OR IT IS WAITING AT A SELECTIVE_WAIT STATEMENT WITH AN OPEN 42-- ALTERNATIVE STARTING WITH SUCH AN ACCEPT STATEMENT). IT ALSO 43-- REQUIRES THAT THE ENTRY CALL BE CANCELLED IF THE CALLED TASK 44-- IS NOT AT SUCH A POINT. ON THE OTHER HAND, THE SEMANTICS OF THE 45-- SELECTIVE_WAIT STATEMENT WITH AN 'ELSE' PART SPECIFIES THAT 46-- THE 'ELSE' PART MUST BE SELECTED IF NO 'ACCEPT' ALTERNATIVE 47-- CAN BE IMMEDIATELY SELECTED, AND THAT SUCH AN ALTERNATIVE 48-- IS DEEMED TO BE IMMEDIATELY SELECTABLE ("SELECTION OF ONE SUCH 49-- ALTERNATIVE OCCURS IMMEDIATELY"), AND A CORRESPONDING RENDEZVOUS 50-- POSSIBLE, IF AND ONLY IF THERE IS A CORRESPONDING ENTRY CALL 51-- W A I T I N G TO BE ACCCEPTED. A "CONDITIONAL ENTRY CALL" 52-- NEVER WAITS, AND IS NEVER ENTERED IN WAIT QUEUES; IT TAKES 53-- THE 'ELSE' PART INSTEAD. 54 55 56-- NOTE: IF THIS TEST PROGRAM HANGS UP, THE COMPILER WILL BE DEEMED 57-- TO HAVE FAILED. 58 59 60-- RM 3/19/82 61 62 63WITH REPORT; USE REPORT; 64PROCEDURE C97201X IS 65 66 RENDEZVOUS_OCCURRED : BOOLEAN := FALSE ; 67 68 CALLER_TAKES_WRONG_BRANCH : BOOLEAN := TRUE ; 69 SERVER_TAKES_WRONG_BRANCH : BOOLEAN := TRUE ; 70 QUEUE_NOT_EMPTY : BOOLEAN := FALSE ; 71 72BEGIN 73 74 75 TEST ("C97201X", "CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF" & 76 " BOTH PARTNERS REFUSE TO WAIT" ); 77 78 79 DECLARE 80 81 82 TASK T IS 83 ENTRY SYNCHRONIZE ; 84 ENTRY DO_IT_NOW_ORELSE( DID_YOU_DO_IT : IN OUT BOOLEAN); 85 ENTRY KEEP_ALIVE ; 86 END T ; 87 88 89 TASK BODY T IS 90 BEGIN 91 92 93 ACCEPT SYNCHRONIZE ; 94 95 96 IF DO_IT_NOW_ORELSE'COUNT /= 0 THEN 97 QUEUE_NOT_EMPTY := TRUE ; 98 END IF; 99 100 101 SELECT 102 ACCEPT DO_IT_NOW_ORELSE 103 ( DID_YOU_DO_IT : IN OUT BOOLEAN ) 104 DO 105 DID_YOU_DO_IT := TRUE ; 106 END ; 107 ELSE -- (I.E. TASK ADOPTS NO-WAIT POLICY) 108 -- 'ELSE' BRANCH MUST THEREFORE BE CHOSEN 109 SERVER_TAKES_WRONG_BRANCH := FALSE ; 110 END SELECT; 111 112 113 IF DO_IT_NOW_ORELSE'COUNT /= 0 THEN 114 QUEUE_NOT_EMPTY := TRUE ; 115 END IF; 116 117 118 ACCEPT KEEP_ALIVE ; -- TO PREVENT THIS SERVER TASK FROM 119 -- TERMINATING IF IT GETS TO 120 -- THE NO-WAIT MEETING-PLACE 121 -- AHEAD OF THE CALLER (WHICH 122 -- WOULD LEAD TO A SUBSEQUENT 123 -- TASKING_ERROR AT THE TIME OF 124 -- THE NO-WAIT CALL). 125 126 127 END T ; 128 129 130 BEGIN 131 132 133 T.SYNCHRONIZE ; -- TO MINIMIZE THE N E E D TO WAIT 134 135 136 SELECT 137 T.DO_IT_NOW_ORELSE ( RENDEZVOUS_OCCURRED ); 138 ELSE -- (I.E. CALLER TOO ADOPTS A NO-WAIT POLICY) 139 -- MUST THEREFORE CHOOSE THIS BRANCH 140 CALLER_TAKES_WRONG_BRANCH := FALSE ; 141 END SELECT; 142 143 144 T.KEEP_ALIVE ; -- THIS ALSO UPDATES THE NONLOCALS 145 146 147 END; -- END OF BLOCK CONTAINING THE NO-WAIT ENTRY CALL 148 149 150 IF RENDEZVOUS_OCCURRED 151 THEN 152 FAILED( "RENDEZVOUS OCCURRED" ); 153 END IF; 154 155 IF CALLER_TAKES_WRONG_BRANCH OR 156 SERVER_TAKES_WRONG_BRANCH 157 THEN 158 FAILED( "WRONG BRANCH TAKEN" ); 159 END IF; 160 161 IF QUEUE_NOT_EMPTY 162 THEN 163 FAILED( "ENTRY QUEUE NOT EMPTY" ); 164 END IF; 165 166 167 RESULT; 168 169 170END C97201X ; 171