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IDProjectCategoryView StatusDate SubmittedLast Update
0007798Part 01: TTCN-3 Core LanguageNew Featurepublic21-09-2018 08:0708-01-2020 09:25
ReporterJacob Wieland - Spirent 
Assigned ToGyorgy Rethy 
PrioritynormalSeverityminorReproducibilityhave not tried
StatusclosedResolutionfixed 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version4.12.1 (published 2020-05) 
Summary0007798: Address problems with implicit default alt invocation
DescriptionThere's some problems with default alts that sometimes lead to surprising/unexpected results for those developing testcases.

A very common pattern is:

t.start;
t.timeout;

Almost nobody expects default alternatives to be evaluated when checking for the timeout. But, if some default alternative like

alt { [] p.receive { repeat } }

is active, this will read all messages from the port p while waiting for the timeout (which might carry significance for the rest of the testcase).

Another of those patterns is

comp.start(..)
comp.done;

A similar problem is if there are multiple channels of communication like the sync communication between components or upper tester communication.
In such instances, while waiting for the answer on port p1, default alts reading messages from another port can influence the test result negatively.

A possible way to deal with this problem is to add boolean component variables and use them for all guards in default alternatives that should not be active all the time. It is then necessary to set/unset these flags before every alt statement.

Of course, this requires a lot of additional code and is very error prone if the number of flags gets bigger and possibly needs to be amended whenever a new default alternative is added to the testcase.

Ideas to address this problem:

1)
Default alternatives should be added a category upon activation and alt statements should allow giving one (or maybe a list) of such categories whose defaults should be active.

2)
For simple non-port alternatives (short form without syntactically enclosing alt like given above), normal defaults should either never be active (unless they are marked specially upon activation) or some modifier @nodefault could be placed in front of them to make it more explicit (to avoid backward incompatibility issues)

3)
Implicity deactivate all alternatives in defaults which do not deal with the entities in the non-default alt-part. E.g. if an alt statement only treats messages on port p (like the upper tester port), alternatives for ports mapped to the system under test should be inactive for the duration of that alt statement.

Of course, while option 3, in my opinion, would be the most logical solution wich requires the least amount of change by the users and as it is the closest to what people expect when they write an alt statement, it is also the most backward incompatible one (though some of the 'incompability' would probably result in fixing unintended behavior in existing, standardized test suites)

As a compromise between 1 and 3 which is not backward incompatible, the categories given to the alt statement could be the the covered ports/timers/components as a list (normally one) with an additional short-form which results in the semantics of 3 (i.e. active for those entities that are covered by the non-default alternatives).

alt (p, t) { [] p.receive(X) {} [] t.timeout {} }
// no default alternatives for things not happening on p or t

alt (?) { [] p.receive(X) {} [] t.timeout {} }
// same semantics as above
TagsNo tags attached.
Clause Reference(s)20.2, C.5
Source (company - Author)Spirent - Jacob Wieland
Attached Filesdocx file icon CR7798.docx [^] (192,796 bytes) 06-08-2019 14:59
docx file icon CR7798-2.docx [^] (366,108 bytes) 07-08-2019 12:47
docx file icon CR7798-3.docx [^] (296,378 bytes) 07-08-2019 13:34

- Relationships

-  Notes
(0015207)
Jens Grabowski (manager)
08-10-2018 14:49

 STF discussion: Usefull extensions. It needs to be checked how the extensions may become part of existing features (e.g., call, wait (RT extension), stopping/starting of ports).
(0015374)
Kristóf Szabados (reporter)
06-08-2019 12:28

 STF discussion: the @nodefault solution will be elaborated. The semantics should be to ignore all activated defaults for the duration of the following alt statement.
(0015376)
Jacob Wieland - Spirent (reporter)
06-08-2019 14:59

 please review
(0015401)
Tomas Urban (developer)
07-08-2019 12:50

 The proposal is fine. I only added missing BNF rules, updated syntax of the related statements and added a restriction on when the modifier can be used. Please check.
(0015405)
Jacob Wieland - Spirent (reporter)
07-08-2019 13:34

 Renamed ReceivingCommunicationStatement to ReceivingStatement and added missing CheckStatement to it in BNF
(0015606)
Gyorgy Rethy (reporter)
08-01-2020 09:25

 Implemented in final draft V4.11.4

- Issue History
Date Modified Username Field Change
21-09-2018 08:07 Jacob Wieland - Spirent New Issue
08-10-2018 14:49 Jens Grabowski Note Added: 0015207
08-10-2018 14:50 Jens Grabowski Assigned To => Jens Grabowski
08-10-2018 14:50 Jens Grabowski Status new => assigned
06-08-2019 12:28 Kristóf Szabados Note Added: 0015374
06-08-2019 12:28 Kristóf Szabados Assigned To Jens Grabowski => Jacob Wieland - Spirent
06-08-2019 14:59 Jacob Wieland - Spirent File Added: CR7798.docx
06-08-2019 14:59 Jacob Wieland - Spirent Note Added: 0015376
06-08-2019 14:59 Jacob Wieland - Spirent Assigned To Jacob Wieland - Spirent => Tomas Urban
06-08-2019 14:59 Jacob Wieland - Spirent Status assigned => confirmed
07-08-2019 12:47 Tomas Urban File Added: CR7798-2.docx
07-08-2019 12:50 Tomas Urban Note Added: 0015401
07-08-2019 12:50 Tomas Urban Assigned To Tomas Urban => Jacob Wieland - Spirent
07-08-2019 13:34 Jacob Wieland - Spirent File Added: CR7798-3.docx
07-08-2019 13:34 Jacob Wieland - Spirent Note Added: 0015405
07-08-2019 13:35 Jacob Wieland - Spirent Status confirmed => resolved
07-08-2019 13:35 Jacob Wieland - Spirent Resolution open => fixed
07-08-2019 13:35 Jacob Wieland - Spirent Assigned To Jacob Wieland - Spirent => Gyorgy Rethy
08-01-2020 08:54 Gyorgy Rethy Project TTCN-3 Change Requests => Part 01: TTCN-3 Core Language
08-01-2020 09:25 Gyorgy Rethy Note Added: 0015606
08-01-2020 09:25 Gyorgy Rethy Status resolved => closed
08-01-2020 09:25 Gyorgy Rethy Fixed in Version => 4.12.1 (published 2020-05)

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