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