In message <[email protected]>, Risto Vaarandi writes: >The users who have used named pipe inputs probably know that SEC keeps >the named pipe inputs open at all times, even when the writers >disappear. However, it is hard to achieve with a pipe opened in >read-only mode, since after all writers have closed the pipe, every >subsequent read always returns EOF, and calls to select(2) always >indicate the availability of data. To fix this issue, the pipe has to be >closed and reopened. > >In the current code, SEC uses a slightly different approach -- it opens >the pipe in read-write mode, although in never writes into the pipe. >However, this guarantees that there is always at least one writer on the >pipe, and thus reopening is not needed. Nevertheless, recently I noticed >in some man pages that POSIX does not encourage opening named pipes in >read-write mode. Also, read-write mode has one small drawback -- SEC >must have a write-permission for the pipe, although this permission is >of course never used. This requirement must be therefore confusing to >the users, although it is explained in the FAQ. > >I'd like to ask a question from the users -- would you favor a change in >the named pipe handling and the use of the read-only mode, or do you >think the current approach is good enough? I would especially welcome >comments from the people with system programming experience. You can >also reply to my private e-mail, if you don't want to discuss the issue >in the mailing list.
It has been a while but I seem to remember an issue with either pipes or unix domain sockets where an open would not return till the other end of the pipe/socket was connected. I think it was the reader that blocked but I am not sure. My concern is that this senario happens: writers to the pipe start writing and block when pipe fills sec opens and reads writers close the pipe and exits sec opens pipe but because there is no writer it blocks badness ensues from: http://www.unixguide.net/unix/programming/2.10.3.shtml looks like there is a noblock flag you can use to prevent this, so ti may not be an issue here since you can use the flag from perl (I hope). -- -- rouilj John Rouillard =========================================================================== My employers don't acknowledge my existence much less my opinions. ------------------------------------------------------------------------------ How ServiceNow helps IT people transform IT departments: 1. A cloud service to automate IT design, transition and operations 2. Dashboards that offer high-level views of enterprise services 3. A single system of record for all IT processes http://p.sf.net/sfu/servicenow-d2d-j _______________________________________________ Simple-evcorr-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/simple-evcorr-users
