On Thu, Jun 29, 2006 at 11:36:41PM -0400, Lev Bishop wrote: >On 6/29/06, Christopher Faylor wrote: >>The idea of using threads for pipe writing has been bounced around for >>a long time. It doesn't solve the select problem if there are multiple >>processes writing to one pipe. That is not a completely unusual event, >>unfortunately. > >Could you be more specific on how it doesn't solve the select problem >in when there are multiple processes writing on the pipe? As far as I >can tell, if (and its a big if) we can build something with threads >that works for a single process, it should work just as well for >multiple processes. Can you give an example sequence of writes and >selects that illustrates the problem? (Not that I think the thread >approach is without problems, I just can't see this one).
Ok. I just skimmed the proposal before and now I have read it more thoroughly. The multi-process problem that I was thinking about may not be there but it still doesn't seem very foolproof. If I understand the plan correctly, in the scenario where select says it's ok to write but it really isn't, the write would return as if it succeeded and a writer thread would be created which sits around trying to empty the pipe. If this happened with a bunch of processes writing to a pipe, it seems like there would be potential ordering problems if, say, a master process was telling subprocesses to write to a pipe in a round robin fashion. In that scenario, if you have n processes, you could conceivably have n people, blocking waiting to write to a pipe and the writes might be executed in random order. Also, in the sequence of events: does select say I can write to the pipe? yes: write to the pipe no: do something else The "do something else" will always be "off-by-one" since we can't actually detect if it is ok to write to a pipe until we actually do the write to the pipe. cgf -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
