To: J3 J3/14-167 From: Reinhold Bader Subject: Delete STAT from EVENT WAIT Date: 2014 June 06 References: N2007, N2013 Discussion: ~~~~~~~~~~~ In my vote in N2013 I complained about EVENT WAIT potentially hanging forever if image failure occurs. (I consider a stopped image that has not issued a needed EVENT POST a programming error). This was based on the expectation that if a STAT= is specified, the statement should return with e.g., STAT_FAILED_IMAGE if an image has failed. However, the latter does not make sense because there are many situations where the EVENT WAIT will complete successfully regardless that an image has failed. Therefore it is suggested to instead delete the sync-stat specification from EVENT WAIT. An application designed for safety against image failure needs to use EVENT_QUERY and maybe extra EVENT POST statements to assure that no hangs can happen in this context. EDITS to N2007: ~~~~~~~~~~~~~~~ [16:5] Delete "or sync-stat" [16:11] Replace "or an error condition occurs, and" by "," [16:12] Delete "if no error condition occurs," [16:16+] At the end of NOTE 6.3, add "Furthermore, because the processor cannot know which image will issue a matching EVENT POST, there is no facility for continuing execution if an image failure occurs. It is the programmer's responsibility to avoid hangs by appropriate use of the EVENT_QUERY intrinsic, of methods for diagnosing image failure, and possibly execution of additional EVENT POST statements." [33:17], [33:26], [33:31], [33:34] Delete "EVENT WAIT,", four times. FURTHER COMMENTS: ~~~~~~~~~~~~~~~~~~ (1) Discussion on the mailing list showed that it may be desirable to retain the STAT variable in order to be able to diagnose specific error conditions, including deadlocks. If this is decided, some of the above edits fall away and the NOTE text must be changed. (2) There is some interaction of the above edits with 14-148r1 if the suggestions in that paper are accepted.