1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
|
-- 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 ;
|
